4.3w low power
Pages :
1 [2]
5693dtcd
08-21-2007, 12:05 AM
Check the ignition control module.
I tried a different one and the old one was tested when it was in the shop. No difference.
I tried a different one and the old one was tested when it was in the shop. No difference.
5693dtcd
08-29-2007, 11:11 PM
Hey there everyone-
I was unable to do an injector balance test. From some of the techs I talked to and the miles on the vehicle I went ahead and replaced the injector "spider " assy. i came away with a very slight improvement.
I hooked it up to a scanner and the timing still retards. I work at a medium duty GMC dealer. I was able to look up on the computer, per VIN, a module located inside the VCM. It is called a Knock sensor module, p/n 16208961. If this is bad- would it cause the timing to retard?
Let me know if you have ever seen this problem.
Thanks
I was unable to do an injector balance test. From some of the techs I talked to and the miles on the vehicle I went ahead and replaced the injector "spider " assy. i came away with a very slight improvement.
I hooked it up to a scanner and the timing still retards. I work at a medium duty GMC dealer. I was able to look up on the computer, per VIN, a module located inside the VCM. It is called a Knock sensor module, p/n 16208961. If this is bad- would it cause the timing to retard?
Let me know if you have ever seen this problem.
Thanks
MT-2500
08-30-2007, 09:45 AM
Hey there everyone-
I was unable to do an injector balance test. From some of the techs I talked to and the miles on the vehicle I went ahead and replaced the injector "spider " assy. i came away with a very slight improvement.
I hooked it up to a scanner and the timing still retards. I work at a medium duty GMC dealer. I was able to look up on the computer, per VIN, a module located inside the VCM. It is called a Knock sensor module, p/n 16208961. If this is bad- would it cause the timing to retard?
Let me know if you have ever seen this problem.
Thanks
That thing is giving you a fit.:grinyes:
The knock sensor module picks up the knock sensor signal and can and should retard the timing if a knock is present.
You might try and unplug the knock sensor and see what it does.
Check actual engine timing with a timing light and see if it matches the VCM/pcm readings.
The VCM gets it timing reference from the crankskaft sensor.
You might want to check it real close to.
If you have a lab scope it works goos on checking sensors.
But also remember the camshaft retard setting has nothing to do with the actual engine timing.
It only centers the dist rotor to fire direct on the plug wire terminal.
Is there any VCM reflashes out for your truck or tsb on it?
Good luck.
MT
I was unable to do an injector balance test. From some of the techs I talked to and the miles on the vehicle I went ahead and replaced the injector "spider " assy. i came away with a very slight improvement.
I hooked it up to a scanner and the timing still retards. I work at a medium duty GMC dealer. I was able to look up on the computer, per VIN, a module located inside the VCM. It is called a Knock sensor module, p/n 16208961. If this is bad- would it cause the timing to retard?
Let me know if you have ever seen this problem.
Thanks
That thing is giving you a fit.:grinyes:
The knock sensor module picks up the knock sensor signal and can and should retard the timing if a knock is present.
You might try and unplug the knock sensor and see what it does.
Check actual engine timing with a timing light and see if it matches the VCM/pcm readings.
The VCM gets it timing reference from the crankskaft sensor.
You might want to check it real close to.
If you have a lab scope it works goos on checking sensors.
But also remember the camshaft retard setting has nothing to do with the actual engine timing.
It only centers the dist rotor to fire direct on the plug wire terminal.
Is there any VCM reflashes out for your truck or tsb on it?
Good luck.
MT
5693dtcd
08-30-2007, 10:54 PM
That thing is giving you a fit.:grinyes:
The knock sensor module picks up the knock sensor signal and can and should retard the timing if a knock is present.
You might try and unplug the knock sensor and see what it does.
Check actual engine timing with a timing light and see if it matches the VCM/pcm readings.
The VCM gets it timing reference from the crankskaft sensor.
You might want to check it real close to.
If you have a lab scope it works goos on checking sensors.
But also remember the camshaft retard setting has nothing to do with the actual engine timing.
It only centers the dist rotor to fire direct on the plug wire terminal.
Is there any VCM reflashes out for your truck or tsb on it?
Good luck.
MT
I will have to check on tsb's. I finally found a knock sensor located at the back of the engine. The parts breakdown lists 2 but illustrates 1. The one I found is next to the oil pressure sensor just to the left of the distributor. The fuel supply and return pass right over it. Its is going to be difficult to even unplug. I can see it and even touch it but I cant disconnect it. Do you know where the second one is at?
The only reason I havnt looked at it before is when I checked it with the scanner the voltage fluctuated indicating it was working. If it runs great with it unplugged, do I need a new sensor or module? Other than a new computer that's the only thing that retards the timing, I think. I'll checkthe crank sensor sometime also. I'm taking it easy this weekend though. I'll check it next week. Have a good Labor Day Weekend!!
The knock sensor module picks up the knock sensor signal and can and should retard the timing if a knock is present.
You might try and unplug the knock sensor and see what it does.
Check actual engine timing with a timing light and see if it matches the VCM/pcm readings.
The VCM gets it timing reference from the crankskaft sensor.
You might want to check it real close to.
If you have a lab scope it works goos on checking sensors.
But also remember the camshaft retard setting has nothing to do with the actual engine timing.
It only centers the dist rotor to fire direct on the plug wire terminal.
Is there any VCM reflashes out for your truck or tsb on it?
Good luck.
MT
I will have to check on tsb's. I finally found a knock sensor located at the back of the engine. The parts breakdown lists 2 but illustrates 1. The one I found is next to the oil pressure sensor just to the left of the distributor. The fuel supply and return pass right over it. Its is going to be difficult to even unplug. I can see it and even touch it but I cant disconnect it. Do you know where the second one is at?
The only reason I havnt looked at it before is when I checked it with the scanner the voltage fluctuated indicating it was working. If it runs great with it unplugged, do I need a new sensor or module? Other than a new computer that's the only thing that retards the timing, I think. I'll checkthe crank sensor sometime also. I'm taking it easy this weekend though. I'll check it next week. Have a good Labor Day Weekend!!
5693dtcd
09-05-2007, 11:10 PM
The check engine light came on over the weekend. I have a code P0420 for a catalyst efficiency low on bank 1.
I also have a code P0304 misfire on number 4.
The code P0420 is what has me concerned. What would cause a this code?
I also have a code P0304 misfire on number 4.
The code P0420 is what has me concerned. What would cause a this code?
MT-2500
09-06-2007, 09:55 AM
The check engine light came on over the weekend. I have a code P0420 for a catalyst efficiency low on bank 1.
I also have a code P0304 misfire on number 4.
The code P0420 is what has me concerned. What would cause a this code?
420 and 430 codes can be caused by engine running problems.
Fix missfire and engine running problems first.
Then clear codes and see if 420 or any other codes come back.
MT
I also have a code P0304 misfire on number 4.
The code P0420 is what has me concerned. What would cause a this code?
420 and 430 codes can be caused by engine running problems.
Fix missfire and engine running problems first.
Then clear codes and see if 420 or any other codes come back.
MT
5693dtcd
09-10-2007, 09:46 PM
That thing is giving you a fit.:grinyes:
The knock sensor module picks up the knock sensor signal and can and should retard the timing if a knock is present.
You might try and unplug the knock sensor and see what it does.
Check actual engine timing with a timing light and see if it matches the VCM/pcm readings.
The VCM gets it timing reference from the crankskaft sensor.
You might want to check it real close to.
If you have a lab scope it works goos on checking sensors.
But also remember the camshaft retard setting has nothing to do with the actual engine timing.
It only centers the dist rotor to fire direct on the plug wire terminal.
Is there any VCM reflashes out for your truck or tsb on it?
Good luck.
MT
It was so much work just to get to the knock sensor to even try to unplug it,I went ahead and replaced the knock sensor. it did not make any difference. I have checked for TSB's. I found one that has something to do with a transmission pressure switch. It bassically states that if the pressure is out of spec - to call the tech hotline. I just don't see how it has anything to do the tranny. Setting in neutral or park it still runs poorly.
I've been told that if the cranksensor was bad, it would have a hard start or no start condition. It starts good.
Thanks.
The knock sensor module picks up the knock sensor signal and can and should retard the timing if a knock is present.
You might try and unplug the knock sensor and see what it does.
Check actual engine timing with a timing light and see if it matches the VCM/pcm readings.
The VCM gets it timing reference from the crankskaft sensor.
You might want to check it real close to.
If you have a lab scope it works goos on checking sensors.
But also remember the camshaft retard setting has nothing to do with the actual engine timing.
It only centers the dist rotor to fire direct on the plug wire terminal.
Is there any VCM reflashes out for your truck or tsb on it?
Good luck.
MT
It was so much work just to get to the knock sensor to even try to unplug it,I went ahead and replaced the knock sensor. it did not make any difference. I have checked for TSB's. I found one that has something to do with a transmission pressure switch. It bassically states that if the pressure is out of spec - to call the tech hotline. I just don't see how it has anything to do the tranny. Setting in neutral or park it still runs poorly.
I've been told that if the cranksensor was bad, it would have a hard start or no start condition. It starts good.
Thanks.
kb3jhp
09-10-2007, 11:25 PM
i would start looking at the computer if you can find a another blazer or jimmy with the same year and drive train you could try the comp out of that if you can find and owner one willing to help you
kb3jhp
09-10-2007, 11:38 PM
also your readings from the scanner with the throtel at 59% eng load should be higher than 25% i think the comp uses the maf senser to no the eng load
MAF gm/sec 43.68 seems high for only 25% load
I threw a code today coming home. P0101 Mass Air circuit out of range.
I did a freeze frame on the scanner and received the following readings
Eng. load 25%
Coolant 149
ST Trim 185
ST trim % 44.5
LT Trim 138
LT Trim % 7.8
ST Trim 2 % -24.2
LT Trim 2 % 0
MAP 29.3
RPM 2306
Veh spd 52 mph
MAF gm/sec 43.68
TPS 59%
MAF gm/sec 43.68 seems high for only 25% load
I threw a code today coming home. P0101 Mass Air circuit out of range.
I did a freeze frame on the scanner and received the following readings
Eng. load 25%
Coolant 149
ST Trim 185
ST trim % 44.5
LT Trim 138
LT Trim % 7.8
ST Trim 2 % -24.2
LT Trim 2 % 0
MAP 29.3
RPM 2306
Veh spd 52 mph
MAF gm/sec 43.68
TPS 59%
5693dtcd
09-18-2007, 10:21 PM
also your readings from the scanner with the throtel at 59% eng load should be higher than 25% i think the comp uses the maf senser to no the eng load
MAF gm/sec 43.68 seems high for only 25% load
I threw a code today coming home. P0101 Mass Air circuit out of range.
I did a freeze frame on the scanner and received the following readings
Eng. load 25%
Coolant 149
ST Trim 185
ST trim % 44.5
LT Trim 138
LT Trim % 7.8
ST Trim 2 % -24.2
LT Trim 2 % 0
MAP 29.3
RPM 2306
Veh spd 52 mph
MAF gm/sec 43.68
TPS 59%
Do you know if the Eng. load affects the ignition timing? I have changed the MAP sensor and the knock sensor. The only other thing that I know of that controls the timing is the computer.
MAF gm/sec 43.68 seems high for only 25% load
I threw a code today coming home. P0101 Mass Air circuit out of range.
I did a freeze frame on the scanner and received the following readings
Eng. load 25%
Coolant 149
ST Trim 185
ST trim % 44.5
LT Trim 138
LT Trim % 7.8
ST Trim 2 % -24.2
LT Trim 2 % 0
MAP 29.3
RPM 2306
Veh spd 52 mph
MAF gm/sec 43.68
TPS 59%
Do you know if the Eng. load affects the ignition timing? I have changed the MAP sensor and the knock sensor. The only other thing that I know of that controls the timing is the computer.
5693dtcd
09-18-2007, 10:25 PM
It was so much work just to get to the knock sensor to even try to unplug it,I went ahead and replaced the knock sensor. it did not make any difference. I have checked for TSB's. I found one that has something to do with a transmission pressure switch. It bassically states that if the pressure is out of spec - to call the tech hotline. I just don't see how it has anything to do the tranny. Setting in neutral or park it still runs poorly.
I've been told that if the cranksensor was bad, it would have a hard start or no start condition. It starts good.
Thanks.
I've changed the knock sensor- no change. Wht about the knock module in the VCM? If it has failed - will it retard it too much? If I remove it will the engine run? If it does and runs good- that might be my problem. Can the VCM be checked out somehow? I don't know of anything else that is making the timing retard so much.
Thanks
I've been told that if the cranksensor was bad, it would have a hard start or no start condition. It starts good.
Thanks.
I've changed the knock sensor- no change. Wht about the knock module in the VCM? If it has failed - will it retard it too much? If I remove it will the engine run? If it does and runs good- that might be my problem. Can the VCM be checked out somehow? I don't know of anything else that is making the timing retard so much.
Thanks
kb3jhp
09-20-2007, 11:58 PM
with a scanner with live data drive and see what your knock retard is and what your ignition advance is. it should advance as far as 45 degrees at times at least thats what mine does and it runs real strong. also watch what it does when you first hit the gas you really should not see any retard i have a live data scan gauge and the only time i see it retard in the timing is when towing and pulling a hill and it starts to ping on gas post back wat you record. also have you checked your tps
5693dtcd
09-22-2007, 08:13 AM
with a scanner with live data drive and see what your knock retard is and what your ignition advance is. it should advance as far as 45 degrees at times at least thats what mine does and it runs real strong. also watch what it does when you first hit the gas you really should not see any retard i have a live data scan gauge and the only time i see it retard in the timing is when towing and pulling a hill and it starts to ping on gas post back wat you record. also have you checked your tps
The scanner I had, I was borrowing. I have since returned it. I have never seen it advance more than 25 degrees. The timing retards to around 10 degrees with the TPS at 100%, RPM around 3000-3500. The engine is trying to get more RPM but it is missing and running rough because of the timing. I tried a new knock module(located inside the VCM), MAF sensor and an air temp sensor in the air intake. NO CHANGE!!!:banghead: I talked with a GM tech who really thought it was the MAF. He thought it was leaning out the mixture too much, this would cause a ping, so it retards the timing. All this leads to low power.
I've had it to two dealers. One was wrong. The other looked at it for 3 or 4 hours. When he told me whatever it is it wont be fixed today I told him to stop what youre doing. I cant afford that kind of comment. I work at a heavy duty truck dealer so I know about diesels and am mechanically inclined. I can do research and install parts myself. This has got me though:banghead:.
The scanner I had, I was borrowing. I have since returned it. I have never seen it advance more than 25 degrees. The timing retards to around 10 degrees with the TPS at 100%, RPM around 3000-3500. The engine is trying to get more RPM but it is missing and running rough because of the timing. I tried a new knock module(located inside the VCM), MAF sensor and an air temp sensor in the air intake. NO CHANGE!!!:banghead: I talked with a GM tech who really thought it was the MAF. He thought it was leaning out the mixture too much, this would cause a ping, so it retards the timing. All this leads to low power.
I've had it to two dealers. One was wrong. The other looked at it for 3 or 4 hours. When he told me whatever it is it wont be fixed today I told him to stop what youre doing. I cant afford that kind of comment. I work at a heavy duty truck dealer so I know about diesels and am mechanically inclined. I can do research and install parts myself. This has got me though:banghead:.
5693dtcd
09-22-2007, 08:16 AM
with a scanner with live data drive and see what your knock retard is and what your ignition advance is. it should advance as far as 45 degrees at times at least thats what mine does and it runs real strong. also watch what it does when you first hit the gas you really should not see any retard i have a live data scan gauge and the only time i see it retard in the timing is when towing and pulling a hill and it starts to ping on gas post back wat you record. also have you checked your tps
While I had the scanner the TPS reading did change smoothly as I moved the pedal. Don't think I havn't thought about changing it though. This thing has got a ghost I cannot figure out.
When it's fixed I'll post what was wrong.
Thanks for reply
While I had the scanner the TPS reading did change smoothly as I moved the pedal. Don't think I havn't thought about changing it though. This thing has got a ghost I cannot figure out.
When it's fixed I'll post what was wrong.
Thanks for reply
Blue Bowtie
09-22-2007, 12:11 PM
I must have missed something... What year is the truck? That will make a difference, since the ECM/PCM would be different, and the control scheme would be different.
5693dtcd
09-22-2007, 10:27 PM
I must have missed something... What year is the truck? That will make a difference, since the ECM/PCM would be different, and the control scheme would be different.
It is a 2000. This thread has been going all summer. I hope that the first entries are still up for others to read. It has all the info at the beginning. I have a poor acceleration - low power problem. The ignition timing is retarding instead of advancing. I'm running out of sensors to replace.
It is a 2000. This thread has been going all summer. I hope that the first entries are still up for others to read. It has all the info at the beginning. I have a poor acceleration - low power problem. The ignition timing is retarding instead of advancing. I'm running out of sensors to replace.
5693dtcd
09-29-2007, 08:04 PM
I know the timing cannot be adjusted. The distributor is bolted down. It cannot be turned. If a new cam postition sensor is installed, or even any of the other sensors, does the VCM have to be programmed to the new sensor? Does the VCM need to "know" a new sensor has been installed?
yjjeep43
10-23-2007, 05:03 PM
Has the problem been found and fixed for this project yet. I am having the same problem and would like to know what the final diagnosis was.
whheezzzz
10-24-2007, 09:50 PM
Ive been reading this thread ever since the beggining did you finally take some C4 to it :icon16: or did you get it up and running, im haveing the same sort of prob on my 93 4.3 blazer and am curious to know if you found the answer thanks :smokin:
5693dtcd
10-25-2007, 09:18 PM
Has the problem been found and fixed for this project yet. I am having the same problem and would like to know what the final diagnosis was.
No I have not found the problem yet. I did take it to a recommended shop. He hooked it up and relearned the computor for me. He stated that since I had replaced the cam sensor the computor didn't know that. After doing so he ran checks on all the electronics. All the sensors are doing what they are supposed to be doing. He could not check the ECM. i'm down to an ECM. I've been busy and it's getting me around so I havn't been able to do much. I'm going to recheck the compression. It doesn't burn any oil so I think the engine is good mechanically. Sorry it's been so long to get a fix. Thanks for reading.
No I have not found the problem yet. I did take it to a recommended shop. He hooked it up and relearned the computor for me. He stated that since I had replaced the cam sensor the computor didn't know that. After doing so he ran checks on all the electronics. All the sensors are doing what they are supposed to be doing. He could not check the ECM. i'm down to an ECM. I've been busy and it's getting me around so I havn't been able to do much. I'm going to recheck the compression. It doesn't burn any oil so I think the engine is good mechanically. Sorry it's been so long to get a fix. Thanks for reading.
5693dtcd
10-25-2007, 09:22 PM
Ive been reading this thread ever since the beggining did you finally take some C4 to it :icon16: or did you get it up and running, im haveing the same sort of prob on my 93 4.3 blazer and am curious to know if you found the answer thanks :smokin:
It has been a long frustrating summer:banghead: Read previous post for a quick summary. I'm going to recheck compression and probably take it in to a dealer. I've been to 2 dealers and 3 ASE shops. No one can figure it out.runaround
I am the kind of person that will not give up though. I've got too much into it to get rid of it. Body wise the truck is in excellent shape. Thanks for reading and I'll keep everyone posted when I find the solution.
It has been a long frustrating summer:banghead: Read previous post for a quick summary. I'm going to recheck compression and probably take it in to a dealer. I've been to 2 dealers and 3 ASE shops. No one can figure it out.runaround
I am the kind of person that will not give up though. I've got too much into it to get rid of it. Body wise the truck is in excellent shape. Thanks for reading and I'll keep everyone posted when I find the solution.
yjjeep43
10-26-2007, 10:49 PM
No I have not found the problem yet. I did take it to a recommended shop. He hooked it up and relearned the computor for me. He stated that since I had replaced the cam sensor the computor didn't know that. After doing so he ran checks on all the electronics. All the sensors are doing what they are supposed to be doing. He could not check the ECM. i'm down to an ECM. I've been busy and it's getting me around so I havn't been able to do much. I'm going to recheck the compression. It doesn't burn any oil so I think the engine is good mechanically. Sorry it's been so long to get a fix. Thanks for reading.
That is where I am at. I have checked everything except the ECM. Like you, mine gets me around town. It just drinks the gas though.
That is where I am at. I have checked everything except the ECM. Like you, mine gets me around town. It just drinks the gas though.
blazes9395
10-27-2007, 12:47 AM
I have been reading this for awhile and I really feel bad for you. I am the same, I just can't stop if something is not right, I just keep going and going at it too. I would probably go nuts if I had your situation though, probably would have the engine apart in my garage by now though....
This has got me thinking two ways, either its running lean/weak as a result of somthing(exhaust restriction), or its a pcm problem. I have a couple of questions, first have you done a compression test on the engine? I'd say you have to make sure you have a good mechanical engine first. Second how is fuel pressure throughout the driving range, have you ever hooked a guage and ran it while your driving. Is it keeping pressure under load? If that checks out, the biggest thing that keeps coming back to me is still a restriced exhaust. I had a similar issue a long time ago with a montana. The vaccuum readings looked good at idle, engine reved alright when on the hoist and in idle, but when you go drive it, it would have no power at all. Engine compression was good, everything looked alright on the scanner but still a no go. I decided to pull the exhaust off, and there it was - restriced exhaust was it, even after a vaccuum guage was on it too. one thing I don't remember on this though was the timing, I don't remember if it had brought the timing back like that.
Timing curve strategies are programmed in the computer. If the engine is timed properly, meaning the timing chain is installed in properly, the distributer is dialed in properly and camshaft timing is within the acceptable threshold, then the engine in general should not be the cause of your problems. It is important the engine is dialed in or you'll just be chasing problems that are not there.
If your ignition system is operating properly, meaning its producing a strong, blue spark at all cylinders, then that pretty much rules the ignition system out too. The ignition system creates spark, the timing of the system is controlled by the PCM as a result of other feedback the system is recieving.
Now what controls timing in itself. Timing is pre-programmed within the PCM, given certain feedback the PCM is reciving as a result of sensor feedback. System load , fuel curve feedback from the 02's, engine temperature etc, all contribute and are calculated by the PCM to achieve the optimum timing stratgies for the engine. Of course feedback is recieved constantly and timing is adjust instantly. Do you notice any difference when the engine is cold as opposed to when its warm? The reason I am asking this is when system is in open loop as opposed to closed loop is there any noticable difference.
I personally cannot see the knock sensors as the issue, because if there was something wrong it would have thrown a fault code and your SES light would be on, assuming of course, you PCM is operating properly.
How is the truck's charging system? Is the charge/output where its suppose to be?
Again assuming a good mechanical, properly dialed in engine, I would probably be chasing the PCM and I would still be looking at an exhaust restriction. Good Luck, and hope you find it soon!
This has got me thinking two ways, either its running lean/weak as a result of somthing(exhaust restriction), or its a pcm problem. I have a couple of questions, first have you done a compression test on the engine? I'd say you have to make sure you have a good mechanical engine first. Second how is fuel pressure throughout the driving range, have you ever hooked a guage and ran it while your driving. Is it keeping pressure under load? If that checks out, the biggest thing that keeps coming back to me is still a restriced exhaust. I had a similar issue a long time ago with a montana. The vaccuum readings looked good at idle, engine reved alright when on the hoist and in idle, but when you go drive it, it would have no power at all. Engine compression was good, everything looked alright on the scanner but still a no go. I decided to pull the exhaust off, and there it was - restriced exhaust was it, even after a vaccuum guage was on it too. one thing I don't remember on this though was the timing, I don't remember if it had brought the timing back like that.
Timing curve strategies are programmed in the computer. If the engine is timed properly, meaning the timing chain is installed in properly, the distributer is dialed in properly and camshaft timing is within the acceptable threshold, then the engine in general should not be the cause of your problems. It is important the engine is dialed in or you'll just be chasing problems that are not there.
If your ignition system is operating properly, meaning its producing a strong, blue spark at all cylinders, then that pretty much rules the ignition system out too. The ignition system creates spark, the timing of the system is controlled by the PCM as a result of other feedback the system is recieving.
Now what controls timing in itself. Timing is pre-programmed within the PCM, given certain feedback the PCM is reciving as a result of sensor feedback. System load , fuel curve feedback from the 02's, engine temperature etc, all contribute and are calculated by the PCM to achieve the optimum timing stratgies for the engine. Of course feedback is recieved constantly and timing is adjust instantly. Do you notice any difference when the engine is cold as opposed to when its warm? The reason I am asking this is when system is in open loop as opposed to closed loop is there any noticable difference.
I personally cannot see the knock sensors as the issue, because if there was something wrong it would have thrown a fault code and your SES light would be on, assuming of course, you PCM is operating properly.
How is the truck's charging system? Is the charge/output where its suppose to be?
Again assuming a good mechanical, properly dialed in engine, I would probably be chasing the PCM and I would still be looking at an exhaust restriction. Good Luck, and hope you find it soon!
5693dtcd
11-25-2007, 07:15 PM
I have been reading this for awhile and I really feel bad for you. I am the same, I just can't stop if something is not right, I just keep going and going at it too. I would probably go nuts if I had your situation though, probably would have the engine apart in my garage by now though....
This has got me thinking two ways, either its running lean/weak as a result of somthing(exhaust restriction), or its a pcm problem. I have a couple of questions, first have you done a compression test on the engine? I'd say you have to make sure you have a good mechanical engine first. Second how is fuel pressure throughout the driving range, have you ever hooked a guage and ran it while your driving. Is it keeping pressure under load? If that checks out, the biggest thing that keeps coming back to me is still a restriced exhaust. I had a similar issue a long time ago with a montana. The vaccuum readings looked good at idle, engine reved alright when on the hoist and in idle, but when you go drive it, it would have no power at all. Engine compression was good, everything looked alright on the scanner but still a no go. I decided to pull the exhaust off, and there it was - restriced exhaust was it, even after a vaccuum guage was on it too. one thing I don't remember on this though was the timing, I don't remember if it had brought the timing back like that.
Timing curve strategies are programmed in the computer. If the engine is timed properly, meaning the timing chain is installed in properly, the distributer is dialed in properly and camshaft timing is within the acceptable threshold, then the engine in general should not be the cause of your problems. It is important the engine is dialed in or you'll just be chasing problems that are not there.
If your ignition system is operating properly, meaning its producing a strong, blue spark at all cylinders, then that pretty much rules the ignition system out too. The ignition system creates spark, the timing of the system is controlled by the PCM as a result of other feedback the system is recieving.
Now what controls timing in itself. Timing is pre-programmed within the PCM, given certain feedback the PCM is reciving as a result of sensor feedback. System load , fuel curve feedback from the 02's, engine temperature etc, all contribute and are calculated by the PCM to achieve the optimum timing stratgies for the engine. Of course feedback is recieved constantly and timing is adjust instantly. Do you notice any difference when the engine is cold as opposed to when its warm? The reason I am asking this is when system is in open loop as opposed to closed loop is there any noticable difference.
I personally cannot see the knock sensors as the issue, because if there was something wrong it would have thrown a fault code and your SES light would be on, assuming of course, you PCM is operating properly.
How is the truck's charging system? Is the charge/output where its suppose to be?
Again assuming a good mechanical, properly dialed in engine, I would probably be chasing the PCM and I would still be looking at an exhaust restriction. Good Luck, and hope you find it soon!
Thank you for responding. I have had the truck checked electronically to see if I have a bad sensor. The tech told me that all the sensors are working properly. When I asked about the PCM he couldn't test it.
I did a compression test today. I tested 4 out of the 6. They all had 170 psi. Is that good? I hope that things will slow down for me after the beginning of the year so that I can get it figured out.
This has got me thinking two ways, either its running lean/weak as a result of somthing(exhaust restriction), or its a pcm problem. I have a couple of questions, first have you done a compression test on the engine? I'd say you have to make sure you have a good mechanical engine first. Second how is fuel pressure throughout the driving range, have you ever hooked a guage and ran it while your driving. Is it keeping pressure under load? If that checks out, the biggest thing that keeps coming back to me is still a restriced exhaust. I had a similar issue a long time ago with a montana. The vaccuum readings looked good at idle, engine reved alright when on the hoist and in idle, but when you go drive it, it would have no power at all. Engine compression was good, everything looked alright on the scanner but still a no go. I decided to pull the exhaust off, and there it was - restriced exhaust was it, even after a vaccuum guage was on it too. one thing I don't remember on this though was the timing, I don't remember if it had brought the timing back like that.
Timing curve strategies are programmed in the computer. If the engine is timed properly, meaning the timing chain is installed in properly, the distributer is dialed in properly and camshaft timing is within the acceptable threshold, then the engine in general should not be the cause of your problems. It is important the engine is dialed in or you'll just be chasing problems that are not there.
If your ignition system is operating properly, meaning its producing a strong, blue spark at all cylinders, then that pretty much rules the ignition system out too. The ignition system creates spark, the timing of the system is controlled by the PCM as a result of other feedback the system is recieving.
Now what controls timing in itself. Timing is pre-programmed within the PCM, given certain feedback the PCM is reciving as a result of sensor feedback. System load , fuel curve feedback from the 02's, engine temperature etc, all contribute and are calculated by the PCM to achieve the optimum timing stratgies for the engine. Of course feedback is recieved constantly and timing is adjust instantly. Do you notice any difference when the engine is cold as opposed to when its warm? The reason I am asking this is when system is in open loop as opposed to closed loop is there any noticable difference.
I personally cannot see the knock sensors as the issue, because if there was something wrong it would have thrown a fault code and your SES light would be on, assuming of course, you PCM is operating properly.
How is the truck's charging system? Is the charge/output where its suppose to be?
Again assuming a good mechanical, properly dialed in engine, I would probably be chasing the PCM and I would still be looking at an exhaust restriction. Good Luck, and hope you find it soon!
Thank you for responding. I have had the truck checked electronically to see if I have a bad sensor. The tech told me that all the sensors are working properly. When I asked about the PCM he couldn't test it.
I did a compression test today. I tested 4 out of the 6. They all had 170 psi. Is that good? I hope that things will slow down for me after the beginning of the year so that I can get it figured out.
5693dtcd
01-22-2008, 08:24 PM
I finally found the problem!!!!! The y pipe is double walled. The inner pipe was coming apart on the right bank. I took it to a GM dealer. When he showed it to me he said that it had him stumped. When he removed th O2 sensor on the right side he noticed something inside the pipe. That's when he saw the inside pipe had collapsed!! You cannot see this from the outside. I would imagine most Blazers have this design.
Thank you to all who followed this thread and made suggestions!
Thank you to all who followed this thread and made suggestions!
5693dtcd
01-22-2008, 08:29 PM
If you ever find the cause, PLEASE make sure to post the fix. I also have a 2000 Blazer (125,000 miles) that suffers from relatively low power despite more-or-less everything being new AC Delco parts, good oil and fuel pressure and no codes whatsoever. I can live with mine, but I know the power is not nearly what it should be, and I wouldn't even try to tow with it. I have been monitoring the board for quite a while now, and it seems that there is some problem peculiar to 2000 Blazers that causes this problem -- although I've never seen a solution. Whenever I have seen a "low power" post with no other problems, more often than not it seems to involve a 2000. A somewhat odd sidenote -- a little while after I replaced my lower intake gasket, I ran a quart of block flushing solvent in the crankcase for the recommended number of minutes, drained it and put in fresh oil and filter. During the test drive, it rode like I had installed a supercharger on the vehicle -- the increase in power was beyond incredible -- it seemed even better than when I bought it new. After that, the power gradually decreased over a few hundred miles and went back to "normal" since then, which was over a year ago. I've always changed the oil and filter every 3000 miles from new, so I assumed it was not a general sludge problem. I don't know what any of this means (is there some offending senser that the block flush temporarily cleaned?), or whether it could be related to the problem you are having. But anyway, good luck finding your problem.
I know it took a LONG time to fix it but I finally found my problem. The y pipe is double walled. The inner pipe was coming apart on the right side. I took it to a GM shop and the only way he found it was when he remove the O2 sensor on the right side. He notice something inside the pipe. It was the inside wall fallen out of place and plugging the exhaust. Midas put on a new y pipe for $300.00. Runs like a madman now!!! It is so good to have it running again.!! I hope you get this thread so that you can get you Y pipe checked. Good luck
I know it took a LONG time to fix it but I finally found my problem. The y pipe is double walled. The inner pipe was coming apart on the right side. I took it to a GM shop and the only way he found it was when he remove the O2 sensor on the right side. He notice something inside the pipe. It was the inside wall fallen out of place and plugging the exhaust. Midas put on a new y pipe for $300.00. Runs like a madman now!!! It is so good to have it running again.!! I hope you get this thread so that you can get you Y pipe checked. Good luck
5693dtcd
01-22-2008, 08:33 PM
I too have the same sluggish acceleration problem along with low MPG. At least in my opinion it is low MPG. This is a new vehicle to me so I only have one average MPG reading based on a half tank of gas - 14.5 MPG. However, to be fair this is based on city driving, in sweltering heat 90 to 100 degrees, with the auto temp set at 78. Is 14.5 MPG normal under those conditions? We just put $1800 into general maintenance repairs that included new spark plugs and wires, fuel filter and alignment with tire rotation and balance. We also made some other maintenance repairs, but they would not have any affect on sluggish acceleration or MPG. I have read the other posts but I have no computer readings to compare the performance. There are no codes showing or trouble lights on that would indicate that there is a problem. Is this poor performance or normal for the 2000 Bravada?
Hey- it took a long time but I found my low power problem The Y pipe for the exhaust was coming apart on the inside. It is double walled. It could not be detected by a visual inspection.
The only way it was found was when the technician remove the O2 sensor and found the inner pipe coming apart.
Hey- it took a long time but I found my low power problem The Y pipe for the exhaust was coming apart on the inside. It is double walled. It could not be detected by a visual inspection.
The only way it was found was when the technician remove the O2 sensor and found the inner pipe coming apart.
5693dtcd
01-22-2008, 08:36 PM
I have been reading this for awhile and I really feel bad for you. I am the same, I just can't stop if something is not right, I just keep going and going at it too. I would probably go nuts if I had your situation though, probably would have the engine apart in my garage by now though....
This has got me thinking two ways, either its running lean/weak as a result of somthing(exhaust restriction), or its a pcm problem. I have a couple of questions, first have you done a compression test on the engine? I'd say you have to make sure you have a good mechanical engine first. Second how is fuel pressure throughout the driving range, have you ever hooked a guage and ran it while your driving. Is it keeping pressure under load? If that checks out, the biggest thing that keeps coming back to me is still a restriced exhaust. I had a similar issue a long time ago with a montana. The vaccuum readings looked good at idle, engine reved alright when on the hoist and in idle, but when you go drive it, it would have no power at all. Engine compression was good, everything looked alright on the scanner but still a no go. I decided to pull the exhaust off, and there it was - restriced exhaust was it, even after a vaccuum guage was on it too. one thing I don't remember on this though was the timing, I don't remember if it had brought the timing back like that.
Timing curve strategies are programmed in the computer. If the engine is timed properly, meaning the timing chain is installed in properly, the distributer is dialed in properly and camshaft timing is within the acceptable threshold, then the engine in general should not be the cause of your problems. It is important the engine is dialed in or you'll just be chasing problems that are not there.
If your ignition system is operating properly, meaning its producing a strong, blue spark at all cylinders, then that pretty much rules the ignition system out too. The ignition system creates spark, the timing of the system is controlled by the PCM as a result of other feedback the system is recieving.
Now what controls timing in itself. Timing is pre-programmed within the PCM, given certain feedback the PCM is reciving as a result of sensor feedback. System load , fuel curve feedback from the 02's, engine temperature etc, all contribute and are calculated by the PCM to achieve the optimum timing stratgies for the engine. Of course feedback is recieved constantly and timing is adjust instantly. Do you notice any difference when the engine is cold as opposed to when its warm? The reason I am asking this is when system is in open loop as opposed to closed loop is there any noticable difference.
I personally cannot see the knock sensors as the issue, because if there was something wrong it would have thrown a fault code and your SES light would be on, assuming of course, you PCM is operating properly.
How is the truck's charging system? Is the charge/output where its suppose to be?
Again assuming a good mechanical, properly dialed in engine, I would probably be chasing the PCM and I would still be looking at an exhaust restriction. Good Luck, and hope you find it soon!
I finally found the cause to my low power. The Y pipe is doubled walled and the inner pipe was coming apart on the right side. The only way the tech found it was when he remove the O2 sensor - he noticed the metal inside the pipe wasn't as it should be. Midas put on a new pipe and it runs great. I bet that this desgn is used on a lot of Blazers. When the exhaust is restricted check more than just the muffler and Cat. Evne if the pipe looks ok on the outside - the inside could still be collapsed.
This has got me thinking two ways, either its running lean/weak as a result of somthing(exhaust restriction), or its a pcm problem. I have a couple of questions, first have you done a compression test on the engine? I'd say you have to make sure you have a good mechanical engine first. Second how is fuel pressure throughout the driving range, have you ever hooked a guage and ran it while your driving. Is it keeping pressure under load? If that checks out, the biggest thing that keeps coming back to me is still a restriced exhaust. I had a similar issue a long time ago with a montana. The vaccuum readings looked good at idle, engine reved alright when on the hoist and in idle, but when you go drive it, it would have no power at all. Engine compression was good, everything looked alright on the scanner but still a no go. I decided to pull the exhaust off, and there it was - restriced exhaust was it, even after a vaccuum guage was on it too. one thing I don't remember on this though was the timing, I don't remember if it had brought the timing back like that.
Timing curve strategies are programmed in the computer. If the engine is timed properly, meaning the timing chain is installed in properly, the distributer is dialed in properly and camshaft timing is within the acceptable threshold, then the engine in general should not be the cause of your problems. It is important the engine is dialed in or you'll just be chasing problems that are not there.
If your ignition system is operating properly, meaning its producing a strong, blue spark at all cylinders, then that pretty much rules the ignition system out too. The ignition system creates spark, the timing of the system is controlled by the PCM as a result of other feedback the system is recieving.
Now what controls timing in itself. Timing is pre-programmed within the PCM, given certain feedback the PCM is reciving as a result of sensor feedback. System load , fuel curve feedback from the 02's, engine temperature etc, all contribute and are calculated by the PCM to achieve the optimum timing stratgies for the engine. Of course feedback is recieved constantly and timing is adjust instantly. Do you notice any difference when the engine is cold as opposed to when its warm? The reason I am asking this is when system is in open loop as opposed to closed loop is there any noticable difference.
I personally cannot see the knock sensors as the issue, because if there was something wrong it would have thrown a fault code and your SES light would be on, assuming of course, you PCM is operating properly.
How is the truck's charging system? Is the charge/output where its suppose to be?
Again assuming a good mechanical, properly dialed in engine, I would probably be chasing the PCM and I would still be looking at an exhaust restriction. Good Luck, and hope you find it soon!
I finally found the cause to my low power. The Y pipe is doubled walled and the inner pipe was coming apart on the right side. The only way the tech found it was when he remove the O2 sensor - he noticed the metal inside the pipe wasn't as it should be. Midas put on a new pipe and it runs great. I bet that this desgn is used on a lot of Blazers. When the exhaust is restricted check more than just the muffler and Cat. Evne if the pipe looks ok on the outside - the inside could still be collapsed.
5693dtcd
01-22-2008, 08:38 PM
That is where I am at. I have checked everything except the ECM. Like you, mine gets me around town. It just drinks the gas though.
Read the rest of the thread and check you Y pipe if you are still having problems.
Read the rest of the thread and check you Y pipe if you are still having problems.
blazes9395
01-22-2008, 11:50 PM
Thats great you got it figured out! Many would have given up on it a long time ago. Internal Y-pipe was restricting it, thats interesting. I knew it sounded like a restriction. Also, more importantly, thanks for posting the solution. At least you can enjoy driving it again...
MT-2500
01-23-2008, 10:19 AM
Thanks for posting back how it went.
Glad you found the problem.
And a good tech that knowed what he was doing.
I have not run to that problem for a long time.
But it goes back to the basic testing to find something like that.
Not many check engine lights or scanners show much there.
Only a good engine capable scanner may have showed a problem wit the 02 sensor.
In your first post we asked for vacuum gauge readings that would have showed a exhaust system restriction.
Good Luck
MT
Glad you found the problem.
And a good tech that knowed what he was doing.
I have not run to that problem for a long time.
But it goes back to the basic testing to find something like that.
Not many check engine lights or scanners show much there.
Only a good engine capable scanner may have showed a problem wit the 02 sensor.
In your first post we asked for vacuum gauge readings that would have showed a exhaust system restriction.
Good Luck
MT
Automotive Network, Inc., Copyright ©2025