99 misfiring, now won't start

Ladies and gentlemen,

I have come to this forum groveling for help. I have a 99 5.3 (I believe, 326?) LT Silverado ex. cab 2wd. It started hesitating and afterfiring, or backfiring, don't know. As I would drive, the message center would start flashing all the codes. A Chevy mech told me that was a sign the computer was going out. Well, it started dying at stop lights and was like it was running on a couple cylinders at times.

I got lucky, when it finally died, and would no longer start, it was in my drive. I got a new PCM? computer? and nothing. Well, the fuel pump was shot. Replaced and nothing, new fuel, nothing. Plenty of pressure, but changed the regulator anyway on a friends advice, nothing. New plugs and wires as the plugs were in pretty sorry shape. Plenty of fire, but nothing. Not even a sputter.

If I spray B-12 chemtool in the intake while the wife cranks, it will start and run as long as the chemtool is going. I checked 6 of the 8 injector leads with noid lights and when cranking, will only flash 2 times and that is it. No matter how long it cranked, only 2 flashes and that was it. Plenty of fire on the 3 plugs I checked, as long as it was cranking, the plugs were firing.

I have so far been unable to find anyone that can bring a computer over to plug in and tell me what codes are showing. I've been told the MAP sensor and told it could be the crank sensor. I'm a little disturbed as nothing is working so far. Any ideas? I really don't want to take it to the chevy dealer or buy more parts without results.

Thanks for any help,
Jeff

Ladies and gentlemen,

I have come to this forum groveling for help. I have a 99 5.3 (I believe, 326?) LT Silverado ex. cab 2wd. It started hesitating and afterfiring, or backfiring, don't know. As I would drive, the message center would start flashing all the codes. A Chevy mech told me that was a sign the computer was going out. Well, it started dying at stop lights and was like it was running on a couple cylinders at times.

I got lucky, when it finally died, and would no longer start, it was in my drive. I got a new PCM? computer? and nothing. Well, the fuel pump was shot. Replaced and nothing, new fuel, nothing. Plenty of pressure, but changed the regulator anyway on a friends advice, nothing. New plugs and wires as the plugs were in pretty sorry shape. Plenty of fire, but nothing. Not even a sputter.

If I spray B-12 chemtool in the intake while the wife cranks, it will start and run as long as the chemtool is going. I checked 6 of the 8 injector leads with noid lights and when cranking, will only flash 2 times and that is it. No matter how long it cranked, only 2 flashes and that was it. Plenty of fire on the 3 plugs I checked, as long as it was cranking, the plugs were firing.

I have so far been unable to find anyone that can bring a computer over to plug in and tell me what codes are showing. I've been told the MAP sensor and told it could be the crank sensor. I'm a little disturbed as nothing is working so far. Any ideas? I really don't want to take it to the chevy dealer or buy more parts without results.

Thanks for any help,
Jeff

If it starts on carb cleaner in intake you have a fuel delivery problem.

Confirm fuel pressure up to specs.
What is the cranking fuel pressure?
Anti theft will shut off fuel injectors.
Does the security light come on and go off key on?

I don't recall the fuel pressure as a I was not was not the one that did the measuring. I was told it was within specs. I am curious about the security problems, will it even start with the security problem? Like I said, the noid lights only flash 2 times when cranking.
I did not even mess with it lately as I am so disgruntled with it. I just want some ideas, hate to take it to the dealer. I like to figure out the problem without taking to the dealer and paying a high price.

Will the MAP sensor keep it from starting? Is there a way to by pass the sensor to check it? I'm about ready to burn it and buy a new truck. Any ideas would be greatly appreciated.

Jeff

I don't recall the fuel pressure as a I was not was not the one that did the measuring. I was told it was within specs. I am curious about the security problems, will it even start with the security problem? Like I said, the noid lights only flash 2 times when cranking.
I did not even mess with it lately as I am so disgruntled with it. I just want some ideas, hate to take it to the dealer. I like to figure out the problem without taking to the dealer and paying a high price.

Will the MAP sensor keep it from starting? Is there a way to by pass the sensor to check it? I'm about ready to burn it and buy a new truck. Any ideas would be greatly appreciated.

Jeff

since it will attempt to start with your adding fuel to the intake you must measure the fuel pressure and follow the fuel pressure testing proceedure, which is listed on these forums for your 5.3L engine....do not rely on repair shops to have this knowledge..

when the fuel pump was replaced many have found issues with the replacement ...bad ground, fuel pump relay , pickup tube, use of pumps other than DELPHI , FUEL REGULATOR , injectors leaking down ....so this is why you must do this fuel pressure testing ...this is step one on no start...

just because it will squirt pretty good, is not an indicator of good fuel pressure as some have found the hard way...you will need a pressure guage ...

The injectors should pulse no matter what fuel pressure is, you need to find a scanner and check out the codes.

if you change the pcm(computer) you will need to get it programmed and have the passlock(security system) re-learned at a dealership. it's also possible you have broken wires in the steering column messing up the passlock system, sometimes a remote start system can cause similar issues. when the passlock doesn't recieve a valid voltage your engine will fire up for about 2 seconds then shut down.

Ok guys... Here is what I've found so far. 58 PSI on fuel pressure, I'm told this is good. Question though, when I disconnect the fuel line and turn the key on, it only squirts fuel for about 2 or 3 seconds. I thought it would squirt until the key was turned off. Is this normal?

The new computer was programmed before I put it in the truck. The guy programming said everything went good and it checked out. Who Know's?

Before it just died on me, there would be times where it would sputter, backfire or afterfire, whetever. Felt like it was running on only a few cylinders at times. Sometimes would die when the truck was stopped. I'm starting to get a little frustrated. Everybody says if I can get my truck to their shop, they can hook up their computer. I'm about to break down and have it towed in.

I put the old computer back in and still nothing. Other than it flashes all the loaded problems on the message center, and the lights flash when the key is off (horn stopped working for some reason, probably burned out from the old computer).

So, fuel pressure is within specs as I believe. Pump only runs for a couple seconds when key is on and line is disconnected, normal?
Injectors only open 2 times when cranking, what sensor/s controls them? Most importantly, how do I check the particular sensor/s?

We are supposed to have a really bad snow storm this weekend so I won't be able to work on it, but I would really like to have some suggestions, I will be needing my truck soon.

All help and suggestions appreciated,
Jeff

Forgot to mention, I spoke with 2 mechanics in the last few days. 1 says my truck does not have a MAP sensor, the other says the MAP sensor is the problem. I have no idea where the sensor is located if it is on there. Where would it be and could that be the problem?

Forgot to mention, I spoke with 2 mechanics in the last few days. 1 says my truck does not have a MAP sensor, the other says the MAP sensor is the problem. I have no idea where the sensor is located if it is on there. Where would it be and could that be the problem?

your fuel will not continue to operate for more than 2 sec with the engine not running so key on 2sec is all you get on the pump pumping....this is a safety design so if you got into an accident and ruptured the line with the engine off,,, the pump will stop..

the crank sensor is under the starter ,, remove starter and inspect wires / connector to it ...it is a failure , not that common, but with your symptoms it is possible..

disconnect the maf connector and see if it starts ...this is another not common but possible cause ..

Ok guys... Here is what I've found so far. 58 PSI on fuel pressure, I'm told this is good. Question though, when I disconnect the fuel line and turn the key on, it only squirts fuel for about 2 or 3 seconds. I thought it would squirt until the key was turned off. Is this normal?

The new computer was programmed before I put it in the truck. The guy programming said everything went good and it checked out. Who Know's?

Before it just died on me, there would be times where it would sputter, backfire or afterfire, whetever. Felt like it was running on only a few cylinders at times. Sometimes would die when the truck was stopped. I'm starting to get a little frustrated. Everybody says if I can get my truck to their shop, they can hook up their computer. I'm about to break down and have it towed in.

I put the old computer back in and still nothing. Other than it flashes all the loaded problems on the message center, and the lights flash when the key is off (horn stopped working for some reason, probably burned out from the old computer).

So, fuel pressure is within specs as I believe. Pump only runs for a couple seconds when key is on and line is disconnected, normal?
Injectors only open 2 times when cranking, what sensor/s controls them? Most importantly, how do I check the particular sensor/s?

We are supposed to have a really bad snow storm this weekend so I won't be able to work on it, but I would really like to have some suggestions, I will be needing my truck soon.

All help and suggestions appreciated,
Jeff

When key is first turned on the fuel pump prime up is about 2 seconds.
That is normal operation.

On engine cranking the fuel pump should turn on and stay on cranking or and when engine starts the fuel pump runs.

Always check fuel pressure when engine is cranking.
Specs are 55-62 lbs pressure.
You should have around 60 lbs to get a good injector squirt cold start.
Also for a full fuel pressure test you need to do a lot more than hook up a gauge and turn key on.

If the VCM has been replaced or any pass lock security stuff the anti theft may have to be reset.

Does the security light come on key on and stay on or go back off?

If it stays on it is tripped and will shut off injector pulse after a 2 second start.
Is that what it is doing?
If so do the relearn on security system.

Does it have the pass lock security system?
If so the relearn is key on for 10 minutes until security light goes out.
And the key off and back on for 10 minutes until light goes out.
he repeat on more time.
Then key off.
Now engine shut start if relearn takes.

And keep a charger on it or a good jumper batter when doing the relearn.


Let us know if relearn gets it started and what the security light is doing.

Or if you have the other security system where the head lights flash and horn honks.
Good Luck.

Forgot to mention, I spoke with 2 mechanics in the last few days. 1 says my truck does not have a MAP sensor, the other says the MAP sensor is the problem. I have no idea where the sensor is located if it is on there. Where would it be and could that be the problem?

the MAP is mounted in the rear of the intake manifold ...this has a connector with 3 pins , 5volts , ground, signal output that varies on intake vacuum...if the engine runs you should get 1.2volts at idle... as the intake vacuum decreases the voltage will rise ...


the ignition relay will cause the injectors not to power up...make sure the voltage at the injectors is always on ...

the grounding of the injector coil is how the injectors open , the other coil connection should always be 12 volts...

Thanks guys. I'm going to try the security relearn first. After that, will check voltages, MAF, crank sensor etc. I'll let you know.

Thanks for the help so far. Still snow on the ground so may be a few days.

Jeff

Here is what I've tried. I unplugged the mass airflow sensor and nothing. Checked the screen and it is clear, nothing clogging it. The only thing showing when I leave the key on is the battery message. Yes it was low and I plugged in the charger. No signes of security. It sputters when I first hit the key, but nothing. Even before the problems, when the key was on it only showed battery.

I unplugged the map sensor. It had carbon buildup and I did my best to clean it out, nothing. I left it unplugged with the maf unplugged and nothing. Not even a spit or sputter from either one unplugged or plugged in. I did not crawl under the thing and check the crank sensor, but I'm leaning towards the crank sensor or map.

How do I check the sensors? I tried using a volt meter and I guess I was not using correctly as I did not get a reading from anything. The MAP had a pretty good load of carbon buildup around the outside edges. Don't know what the inside looked liked, but I dug a nice amount of carbon out of it. I did not crawl under my truck as the ground was really wet and I did not get anything to lay on.
I am going to take off the starter and check the crank sensor leads when the ground dryes out a little more.

Oh, and as far as the security stuff. Well, when I turned the key on, it showed the battery light. After leaving it on for several minutes, it still shows the batter light and does not show the security light. Thats with the battery charger plugged in. It cranks, but nothing.

I guess I'll replace the crank sensor. Is there anything special I need to know about the replacement? Is there any special thing I need to do to time the sensor? If that does not work, I'll replace the MAP sensor, unless any of you have other suggestions.

Jeff

Proper testing in stead of throwing parts at it.

you have ignored the recommendations of the forum members suggestions ...If you have all the answers or just want to spend money on unneeded parts why are you here ?

Double post

Gentlemen,

I appologize for jumping the gun and throwing ideas off the top of my head. I got a little ahead of myself and posted like a fool. I appologize, I am here for help.

I have done more testing and finally came up with a scanner. Here is what I've come up with. I unplugged injectors and put a voltmeter to them. Nothing until it cranks. 2 quick reading then nothing. Just like the noid lights, 2 flashes and thats it.

The 8 coils are all firing, I don't see a ground wire or any other way to test other than putting a spark plug in the wire and laying the plug on metal to see if it fires.

The scanner shows code P 1631, security. I checked the internet and say to do a key relearn after replacing the PCM. I followed the proceedure by MT-2500 and nothing. The code was cleared and did the relearn, nothing. I checked more on the internet and what is strange, the procedure says I will see the security light for about 10 minutes. The security light never came on, with the door open or closed, nothing. Only the battery light. I had the charger connected and showed 78% charge at 12.9 volts.

Any ideas?

Gentlemen,

I appologize for jumping the gun and throwing ideas off the top of my head. I got a little ahead of myself and posted like a fool. I appologize, I am here for help.

I have done more testing and finally came up with a scanner. Here is what I've come up with. I unplugged injectors and put a voltmeter to them. Nothing until it cranks. 2 quick reading then nothing. Just like the noid lights, 2 flashes and thats it.

The 8 coils are all firing, I don't see a ground wire or any other way to test other than putting a spark plug in the wire and laying the plug on metal to see if it fires.

The scanner shows code P 1631, security. I checked the internet and say to do a key relearn after replacing the PCM. I followed the proceedure by MT-2500 and nothing. The code was cleared and did the relearn, nothing. I checked more on the internet and what is strange, the procedure says I will see the security light for about 10 minutes. The security light never came on, with the door open or closed, nothing. Only the battery light. I had the charger connected and showed 78% charge at 12.9 volts.

Any ideas?




you must have a security light ...check all fuses with a voltmeter...this could be the BCM module as well..

with a security issue the engine will start then quickly die...

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Gentlemen,

After checking with the computer, I learned the only 2 places in my town that can program my BCM are the 2 GMC dealers in town. I am a little disturbed as I have replaced everything my friends have told me. Yea, I know I was in need of new plugs and wires, but pressure regulator? who knows, it was very expensive, but what the hay. Without this forum I would have replaced the crank sensor and the sensor on the intake at the rear, I don't remember, its been a long couple of weeks.

I talked to a friend who has a shop and he was looking on his computer with my gripes. he said what he had heard sounds like the BCM, and he could replace the computer, but.... there are 2 places in town that could program it, the chevy and gmc dealers. I told him to replace the computer and the drivers side window guts (since it broke a cable). He had his wrecker come to my house and tow it to his shop. I am getting cost on parts and a discount on labor. Towing was....... NOTHING. I give up, I've done the volt testing and all that has been advised. I really hate this as I like to figure out my problems and fix them. It was a real upset when told it was the bcm and only the gm dealer could program it (nobody in town spent the money for the program).
My truck has been in the shop for over a week and I am awaiting the bill, along with what was wrong. I'll post with the findings, if it is any benifit. I am really upset as it should be an easy fix, without all computer junk. What happened to the good old days?
No security light was the big flag, other computer test's lead him to believe it was the bcm, I don't know, but when it is figured out, I'll let you know.

Jeff

the only way this will be repaired correctly is if the shop has tech's that can troubleshoot electronic equiptment, and have the OEM shop manual to determine why you lost the security LT.

I doubt this is a simple reprogram of the BCM...

please reply with whatever they find that corrects this .