95 engine issues

well i've been having issues with my motor. so i got a scanner and now i can look at what the motor is doing. its opening the egr valve up under a load and the motor looses power. the computer is sensing a knock. anywhere from 143 to as much as 256. the only other thing ive seen is the timing. at idle when its in closed loop its aroun 11-16 advanced. if i give it 7% throttle while power brakeing it, it goes to around 35% and then it senses a knock and opens the egr. it does this while driving to. new map sensor and throttle postion sensor. removed egr today and cleaned just to make sure. any ideas?
its a 95 witht he cpi. and i changed the regulator about 3 weeks ago. this has been going on for a long time.

Low fuel pressure causes a lean mixture which will cause a spark knock. Which injection system do you have? 95 came with CMFI or CSFI. Have you checked fuel pressure and leakdown?

i've checked fuel pressure and leak down. i've even driven the truck while watching the pressure and it never feel below 65psi. it has the cpi spider.

can anyone tell me what the timing should be?

I believe it's 0° ATDC; the computer does the rest.

i need to know what it should read on the scanner.

well the latest update is that i replaced the knock sensors and now it detects no spark knock. but im still having the same issue of the harder i accelerate the more the egr opens unless i floor it. then it stays closed. basically its operating opposite of how it should. what controls this thing?

no ideas here?

EGR should be closed at idle and at wide open throttle. It will vary inbetween there as the ECM sees fit. Sounds like its working correctly.

Fuel pressure at 65psi while the engine is running is too high. With the key on, engine off, fuel pump running, fuel pressure should be 58psi to 64psi on your 95 cmfi system. The pressure must remain above 53psi for 3 to 5 minutes after the fuel pump shuts off. GM does not publish any "engine running " fuel pressure specs, there are far too many variables involved. Typically that system will maintain approximately 53psi at idle, and increase up to whatever the engine off, pump running reading was, as engine load increases.

I see in your signature that you have a K&N intake :nono: They usually cause more trouble than they're worth... Oil residue from the filter will coat the MAF sensor causing it to send a false reading to the PCM. Have you cleaned the sensor lately just to be sure?

it would hold 65 while driving but it did change depending on engine load. at idle it was 58 to 59 if i recall. the truck runs great with the egr unplugged so i dont believe it has to do with fuel or spark. its whatever is controlling the egr. i know the egr is supposed to be open but its work backwards. the more load that is put on the engine the more it opens. less load the more it closes. my parents 98 closes once throttle goes past 30% or something like that. mine just opens more. the intake is a cpi system so there is no maf. and i've replaced the map sensor with no change. i need to know what else controls the egr operation. i've also tried switching ecm's with no luck.

What is the fuel pressure with the key on, engine off, fuel pump running? 65psi is more than that system should EVER produce. If your gauge is accurate, I would suspect a restriction in the fuel return line.

When the ECM is in open loop operation, EGR does not open. When the ECM is in closed loop operation, at idle the EGR valve is closed. As engine RPM and load increases, the ECM opens the EGR valve unless/until WOT ocurrs, then it closes. EGR reduces combustion chamber temperature which reduces detonation, (spark knock). It also reduces NOx, (worse than CO because NOx consumes oxygen.) The ECM has total control over EGR operation and commands it according to data received from various sensors on the engine.

I could be wrong but I think your EGR now sounds like it's working properly if it closes near full throttle. I don't think you can compare a 98 to a 95's operation. They are different systems. I think your timing sounds about right. Does it run OK?

as far as the fuel pressure goes when i checked it, i was at a friends shop. we pulled up on alldata what the specs were and testing and all the pressure read correctly. i cant see anything being wrong with fuel delivery if the truck runs perfectly with the egr unplugged. as for the egr, it follows 100% what the computer tells it to do. i just need to find out is telling the computer to open it. i did get another code the other day that said o2 sensor in bank 1 sensor 2 had low voltage. i reset it and hasn't came back since. its the o2 after the cat. would this sensor effect the egr? with the egr pluged in when you hit the gas to take off it stumbles and then recovers and goes but it feels like your running on 4cyl. unplugged it feels like a v8.

The O2 sensor after the converter monitors catalyst performance ONLY, that's all it does. It has nothing to do with fuel mixture and it does not affect EGR.

I'll do some research on what the parameters are for EGR operation... should be able to get back with an answer tomorrow.

As for Alldata specs on the fuel pressure, I would trust the GM factory shop manual.... 58psi to 64psi. If Alldata is giving you an "engine running" pressure spec, don't believe it, there is none. There are far too many variables involved that affect fuel pressure while the engine is running such as basic engine condition, engine load, percentage of throttle opening, altitude above sea level, ambient temperature, coolant temperature, etc.

Well if it still runs a lot better with the EGR unplugged there might be a problem with the EGR. I don't know what it could be. I think the EGR command is based on the input of several sensor most of them you replaced or aren't throwing codes such as the VSS. Maybe check the wiring harness or maybe the EGR valve is wacked and tricking the ECM/PCM :icon16:.

it never gave a running spec. just bled down, and prime pressure. when we drove it we had a gauge hooked to it and pressure was always up. i have the service book for the truck and it says egr is affected by map sensor, tps, engine coolant temp and ita. but all of them are reading good. do you happen to know what ae clamp is? i saw it on the scanner. sometimes its on and others its off. never stays on though. the new thing i experienced with it today was having the egr plugged into another egr not connected to the engine and i commanded it open 50% or more with a scanner the engine would start to stumble and then rev up and recover. its never done that before. usually it would open it up and run like nothing changed. also tried driving the truck with the dummy egr in place and it was still commanding it to open just like the one attached to the engine.

the new thing i experienced with it today was having the egr plugged into another egr not connected to the engine and i commanded it open 50% or more with a scanner the engine would start to stumble and then rev up and recover. its never done that before. usually it would open it up and run like nothing changed. also tried driving the truck with the dummy egr in place and it was still commanding it to open just like the one attached to the engine.

What kind of scanner do you have? Anyway, do you mean you commanded the EGR valve 50% with the old EGR valve that's installed and the engine didn't stumble before, or this is the first time the dummy EGR caused a stumble? I'm not sure why unhooked EGR would cause a stumble..I don't know if the computer was trying to take counter measure like enrichening in anticipation of the larger EGR flow that didn't actually exist or why it didn't do it before?

What I was saying is it's possible there's nothing wrong with PCM or its sensor inputs in regard to the EGR command but maybe the EGR is not really opening the way it's being commanded and the PCM doesn't realize it?

I'm not saying the EGR valve is bad and replace it, I'm just saying it'd be nice to have that a different one installed and see how it ran :smokin:.

i have a snap on scanner. and yes i didnt remove the old valve. i left it on the engine and using a functional test i commanded it open. i've done this before and never had a issue. it was idling and when i commanded it open is when it stated having issues and revved up to recover. if i have have the egr hooked up the way its designed then that's when if i give it gas it stumbles but that's also cause it opens the egr up to 60% open. i did also pull off the egr and cleaned it. with the engine not running i commanded it to different % and it moved like it should. so i dont believe the valve is bad. just for some reason the computer thinks it needs to open it. even with it unplugged i get 0-6 spark knock so i know spark knock isnt causing it. although while driving the computer is running 34-36' of timing. i'm also running premium fuel. i dont know if that timing is right. i know before when i ran regular i could only get 20 if i was lucky but it had alot of spark knock.

OK I was just saying the computer might be commanding the proper EGR valve percent opening but the EGR valve might be opening further than it's supposed to. It would be hard to tell just how far the EGR is actually opening and the computer might not know it's opening more than commanded. I don't think the earlier model EGR has the on board diagnostic to detect this and set an EGR code like later linear EGRs. I could be wrong. but assuming the wiring harness is sound and the computer is getting the right TPS and Map reading, what else besides a faulty EGR is left besides the ECM itself?

Maybe Old Master can figure out something for EGR %. Maybe your EGR is fine and it hesitates with the EGR hooked up because your CPI is dirty/partially clogged? Sometimes dirty injectors hesistate when engine hot and in closed loop and with EGR because the injector duty cycle is so low.

it has the linear egr valve. as for the duty cycle it runs around 50%. i've seen the computer command the egr to 150% but the duty cycle is at 50 so it opens to 75 or 80.

... i have the service book for the truck and it says egr is affected by map sensor, tps, engine coolant temp and ita. but all of them are reading good. do you happen to know what ae clamp is? i saw it on the scanner. sometimes its on and others its off. never stays on though....

Those are the sensors the ECM gathers data from to determine when and how much EGR to apply.

The "ae clamp" is a mystery, the only thing I can think of is possibly "ac comp" which is the air conditioning compressor. Some OBD systems monitor when the compressor clutch field is energized. That would also explain the on again off again status.

Have you checked crankshaft / camshaft correlation? It must be set as close to zero as possible, plus or minus 2 degrees. Usually, but not always, it will set a P1345 DTC if its too far off.

how do i check it? what do i look for on the scanner? as for the ae clamp it has nothing to do with the a/c. a/c was off and it only came on when the truck started to stumble.

A code reader will not access it. Only the "enhanced" scan tools will access it. Depending on what scan tool you have, it may call it camshaft timing or cam retard, or something along those lines. Flip through the options and it might tell you. It will show a reading in degrees, and will remain constant. If the distributor is removed and not installed correctly, (off a tooth) it will affect cam / crank correlation. The distributor will only lock in one position and is not adjustable. Sometimes it's necessary to grind the distributor mount to "fine tune" it.

as far as i know its never been removed and i've had the truck for 6 years. the scanner i have is the snap on mt 2500 so i can read all the sensors and what they are doing. so do i check this at idle? the other thing i forgot to mention is that i noticed with egr unplugged the idle is inconstant. it idles fine but then drops off like the a/c kicked in but then recovers. the egr never opens during this time. but the ses light is on because the egr is unplugged. is that norm? i know the a/c compressor is off though.

i just checked the scanner and all i have is spark mod and the timing. the timing moves around but the spark mod stays at 0.

how would dirty contacts on the cap and rotor affect this? pulled mine today and theres white powder everywhere. any ideas or why? cap and rotor is maybe a year old.

When the cap and rotor are replaced, silicone dielectric grease is applied to all contacts both inside and out of the cap. When the engine is running, the current passing across the contacts causes the dielectric to crystalize. It looks like corrosion or a white powdery substance. It's suppose to be there, if it's not, somebody didn't do their job when they replaced the cap!

Dirty contacts would not necessarily cause your problem. A more common reason is the aftermarket caps have poor insulation from the tower connection that the wire connects to, to the contact that you see on the inside of the cap. Stray spark jumps around as a result, and causes poor engine performance. AC Delco caps don't have that problem.

well i replaced the cap and rotor with accel one's. no one sold any that had brass in it but accel. the engine runs better but still having issues. next i'm gonna replace the egr valve and see what it does. i'm out of ideas.

Did you ever try fuel cleaner to see if it made an improvement?

When the cap and rotor are replaced, silicone dielectric grease is applied to all contacts both inside and out of the cap. When the engine is running, the current passing across the contacts causes the dielectric to crystalize. It looks like corrosion or a white powdery substance. It's suppose to be there, if it's not, somebody didn't do their job when they replaced the cap!



Electrical is not my strong suit so maybe you could clear something up for me :icon16:. One thing I was never sure of with dielectric grease is how does it not block electrical flow at the connecter where it is needed? Is it because the connector pushes it all away? Seems like some of it would remain there as a film, especially where there is a gap between conducters like cap terminals to rotor.

My understanding of dielectric grease is it keeps moisture and corrosion of of the connecter which is good and also is not very conductive to electricity so it prevent electrical "leaks", which is also good. But that leads me back to my question. Doesn't it add resistance and block electrical flow through the connecter on the contacts or not?

tried seafoam. no luck.

I don't mean to knock seafoam, but that could be more of a problem than a fix. I think you should try a dedicated fuel system/injector cleaner like Techron/ProGard. sometimes even that won't get injectors clean and they need cleaner ran directly through. Anyway maybe the Seafoam works OK as an injector cleaner and that's not the problem.

replaced egr valve. no change.

could it be a timing chain issue? whats the easiest way to check?

could it be a timing chain issue? whats the easiest way to check?

Have you checked compression? that could tell you a lot like late ignition valve timing (timing chain), rings seal, etc. A vaccuum guage can help too. I still think clogged up fuel injector is a possibilty.

no i haven't. well today i went to start the truck. started right up and rpms went to 1400 and then stayed there and then started moving up and down +/- 200rpms. left engine running. grabbed scanner. it said the tps voltage was .68 volts but it said throttle % was 3. turned off truck. waited 10 seconds. restarted and then all was back to normal. tps voltage was .68 and 0% throttle. turned off engine. turned key back on to check map sensor and it just stayed at 1.72 volts. started engine, revved motor and saw it jump up to somewhere around 3 volts. killed engine and rechecked and it was reading 4.some volts like it should. timing when engine saw 3% throttle it was 32 degrees. when everything was working correctly it was at 12-18 and moving around. the other day i swapped the egr valve when i plugged it in the computer said it was calling for it to be open 11% and the actual egr was open 8%. i looked at the valve and it wasn't open at all. i didn't have it installed yet. tried turning on and off no luck. pulled ecm fuse for 5 mins. put back in and everything returned to normal. any ideas whats making this thing screw up?

I don't know, maybe your ECM has some kind of problem or maybe you have scanner problems, but you say it really does runs bad. Hard to say. Maybe someone else here has an idea. It's hard to imagine that your TPS and MAP both were bad then suddenly fixed themselves unless there was a wiring problem or ECM problem, or scanner problem. Maybe check the reference 5V at those sensors? Does this 95 have that OBD1.5 with an OBD II diagnostic connecter and flash eeprom but OBD I software?

its obd2. ecm is on the coolant bottle. im gonna try switching the ecms tomorrow again.

got home to late. didnt get a chance to switch ecms. would i choppy idle tell anything? also i've noticed that when its warm and i come to a stop the idle goes up and down like the a/c compressor is kicking on. i know for a fact it isnt. only does it in drive.

went outside with a light. switched emcs. no change. would a weak ground cause any of this? i measured from ground post on battery to different places on the engine. the best i could get was 107 ohms. any ideas?

From the ground terminal at the battery to any good ground on the vehicle, resistance should be no more than 5 ohms.

so could that be my issue? computer is seeing 14.4 volts.

ECM is seeing 14.4 volts, but is the ECM and the vehicle body seeing a good ground? Check resistance from the ECM ground pin to the negative battery terminal, should be less than 5 ohms. You might have a problem with the body ground, it attaches to the rear of the right cylinder head, or at the ground cable connection from the battery to the engine block.

I was just curious. How were able to swap PCMs on an OBDII with theftdeterent. Didn't you have to reflash the PCM? Its looking like you have wiring/ground problems like old master mentioned. You could still have a mechanicl issue or cloggy injector problems though once you get the electrical sorted out.

theftdeterent? never heard of it. truck runs fine with it.

OK then you're saying now it runs fine with the new PCM? I was just curious so did you just swap a PCM out of another 95 or was it a new reprogammed PCM?

im gonna have to check the ground on sunday. i did however do the ground update for the ecm a while back. the one where you add the wire into the harness. just to eliminate that possibility. the ecm was from another 95 with the cpi and obd2. i never knew there was a such thing as the theft deterrent. can you explain in more detail? it runs fine as in it drives like the other ecm is in it. still opening egr when it shouldn't. i cant see 2 ecms having the exact same issue. where does the ecm get its gound? the engine block or the body? i measured from the intake,a/c compressor and altenator shell and connect the other wire to the batt terminal. then thats when i was getting the reading. i checked it on another car and i only got 5 ohms resistance. could that small extra amount cause all of this?

From 5 ohms to 107 ohms makes a huge difference when it comes to digital electronics. Check both ends of the body ground: On the negative terminal of the battery, there should be a 0 gauge wire and a 10 gage wire. The 0 gage wire goes to the engine block and the 10 gage wire will connect to the body, usually on the radiator support close to the battery. There are other ground straps on the vehicle, usually there's one attached to the bulkhead, (firewall) near the heater hoses and goes to the back of the right cylinder head. That particular ground is usually a braided type cable with eyelets on each end.

I got it now, you're saying no change with the PCM swap. For theft deterrent I was asking if the truck had Passkey or Passlock, but I guess it doesn't. I'm sure you heard of them :icon16:. Well so far it sounds like you have narrowed it down to a poor engine ground. I think if you check all the engine grounds, body grounds, and the ground integrity from the PCM, it'll probably be running better.

i plan to do that tomorrow. i dont think they had pass-lock back then. all i have is keyless entry which is done by a dealer installed alarm.

I wanted to throw a wild guess out there. Do you think the reason you are seeing wider EGR duty if you really are, might be because the PCM is compensating for the lower back pressure exhaust you have on it when does its I/M readiness testing? I'm not sure if the system has that kind of capability or not to tell you the truth. Anyway, if it were compensating it wouldn't affect the engine running bad problem you are having, just possible create wider duty cycles, unless they are fixed.

I wanted to throw a wild guess out there. Do you think the reason you are seeing wider EGR duty if you really are, might be because the PCM is compensating for the lower back pressure exhaust you have on it when does its I/M readiness testing? I'm not sure if the system has that kind of capability or not to tell you the truth. Anyway, if it were compensating it wouldn't affect the engine running bad problem you are having, just possible create wider duty cycles, unless they are fixed.

Some vehicles were designed with a means of measuring backpressure and adjusting EGR accordingly. For example, Ford uses a DPFE sensor, and many manufacturers used a transducer, but this particular system does not have any sensors for measuring exhaust backpressure. Excellent thought though.

Some vehicles were designed with a means of measuring backpressure and adjusting EGR accordingly. For example, Ford uses a DPFE sensor, and many manufacturers used a transducer, but this particular system does not have any sensors for measuring exhaust backpressure. Excellent thought though.

Well I was wondering if this GM system might be able to calcultate EGR flow during the emissions monitor test or whenever by comparing RPM drop to expected for the EGR duty cycle. I doubt this one can but I seem to remember that later model GM EGR can calculate flow without a separate sensor, but I might be mistaken.

cleaned all the ground from the batt. now i get 0 ohms to the engine as well as the ecm. still now change. but i think whatever is going bad is getting worse. my idle is really rough now. as for the egr. this system opens it during decel to see the map change. thats how it checks flow. its not some much im worried about it opening. its that when it opens i loose like half of my power.

I forgot what all you did so far but if the idle's still rough, I think you should go back to checking engine condition-compression test, vaccuum, and consider that it might have dirty injector poppets. I think you should try some Techron fuel injector cleaner and see if it helps.

i know it idles smoother if i make it have a vac leak. i need to check compression yet.

well the latest is that i started it the other day and it started idling high again. hooked up the scanner and it said that the throttle % was at 6% and the idle switch was open but the tps volts was at .66-.68. i revved the engine and the most i could get the injector pulse width to was .8ms. turned off truck. waited 5 seconds. restarted and it was back to norm. rev engine and i saw the injector go over 3.0ms. then i watched egr and noticed it wasn't moving. volts on egr was 1.06 but egr position was 0 and it was being commanded 0. truck the truck for a drive and the entire time it stayed at 0. turned off engine. waited again. restarted and engine was back to opening the egr under load. only 2 things i saw that were different. the egr volts was 1.06 and it said ignition dtc-yes. still no ses.

forgot to add that it was commanding the iac to 150 when it was running high idle. when it calmed down after driving it, it was commanding between 0-2.

checked timing today and timing is in line. no slack in timing chain. changed out distributor with no change. any ideas?

????