Major misfire and unable to communicate with ECU

[Marc91GSX]

Ok I have several problems but only two that I cannot figure out.

Problem 1) My car has a major missfire and I am lost on what it's cause might be. At an idle I can pull the injector plugs off of 1 & 4 the idle barely changes, but if I oull them off of 2 & 3 the car almost dies. As the rpms increase the missfire seems to go away until about 4000 rpms and then it comes back with a vengence. It literaly sounds and feels like I am hitting the rev limiter. I have tried all of the free test that I can think of to narrow this down or fix it but so far nothing has worked. I have swapped coil packs with a known good unit, switched injectors, done a compression check, replaced the plugs, and even gone so far as to pull off the cams and check the lash adjusters to make sure they are not holding the valves open.

Problem 2) I can not get anything to communicate with my ecu. I have tried my laptop with DSMlink, my regular dattalogger, and even a factory scan tool.

I am lost on both of these problems and I am about to give up. I have been fighting with this thing for the past four months and if I do not have them resolved soon I am just going to part this POS out and burn what does not sale. Please help!!!!!

 

[chicagoavenger]

possible leaky caps in the ecu have you pulled the ecu or swapped it out with a friend's? base timing good? timing mark correct?

 

[Marc91GSX]

possible leaky caps in the ecu have you pulled the ecu or swapped it out with a friend's? base timing good? timing mark correct?

The ECU was rebuilt when it was socketed for DSMlink, base timing is set at 5 deg BTDC per the book, and the timing belt is perfect (I have checked it 10 times since this problem has started).

 

[Talesin]

1) Check for spark on 1&4. Use a calibrated spark gap tester. If there's no spark, don't forget to check your power transistor as well as check the impedence of the #1 coil. Failing that, check your CAS. Listen to the #1 and 4 injectors, make sure they're clicking. (Mechanic stethoscope, or take a long screwdriver and put your ear to the handle and place the tip on what you want to listen to.) If you have spark on both, and fuel on both, check the compression.

2) Have you hooked up any of the tools to another DSM to verify that they're working? DSMLink won't connect without the DSMLink EPROM, and the proper settings in the program. I'd inspect the socketing job, if you had DSMLink installed... it could be possible that they may have shorted the EPROM pin pads together if they weren't neat, or even put a cap on backward. 'Regular datalogger?' Which one? Tunerstein can be a bit of a pain to set up. Make sure you're set to use the correct COM port, and use the DRB connection, not the ODBII. Also, make sure you follow the install instructions, or it'll be unable to hook the serial stream. Factory scantool should work without a hitch though. Make sure the ignition is set to 'on', and not just accessory or turned off.


When did all these problems start? When you had the ECU worked on? If so, that's what I'd look at closest.

 

[Marc91GSX]

1) Check for spark on 1&4. Use a calibrated spark gap tester. If there's no spark, don't forget to check your power transistor as well as check the impedence of the #1 coil. Failing that, check your CAS. Listen to the #1 and 4 injectors, make sure they're clicking. (Mechanic stethoscope, or take a long screwdriver and put your ear to the handle and place the tip on what you want to listen to.) If you have spark on both, and fuel on both, check the compression.

2) Have you hooked up any of the tools to another DSM to verify that they're working? DSMLink won't connect without the DSMLink EPROM, and the proper settings in the program. I'd inspect the socketing job, if you had DSMLink installed... it could be possible that they may have shorted the EPROM pin pads together if they weren't neat, or even put a cap on backward. 'Regular datalogger?' Which one? Tunerstein can be a bit of a pain to set up. Make sure you're set to use the correct COM port, and use the DRB connection, not the ODBII. Also, make sure you follow the install instructions, or it'll be unable to hook the serial stream. Factory scantool should work without a hitch though. Make sure the ignition is set to 'on', and not just accessory or turned off.


When did all these problems start? When you had the ECU worked on? If so, that's what I'd look at closest.

I installed DSMlink myself, but the cap replacement and socketing was performed by Steve so I trust that the work was done properly. As for the datalogger, it was just some ebay cheapy that worked fine before I had to rebuild the engine. I sent my laptop and harness to Thomas at ECM tuning to have it checked and everything was working fine, so the problem lies somewhere in my car.

As for the missfire problem, I have tired three different coil packs and my COP and I have also replaced the power transistor. I am on my fourth set of plugs and I have tried gaps from .024-.028. Compression was low on the two cylinders involved but according to the books it was still within spec. ( I am leaning torwards a compression problem ), I have not done a compression check in a a couple of months so I cannot remember the exact numbers, but I will do one tomorrow and post those numbers. I have also not checked to see if the injectors on 1 & 4 are firing so I will check that as well.

Oh yeah I forgot to mention that this engine has less than 200 miles on it, ad I have had the problem since this engine has been running.

 

[staticbrainwash]

When i first got my 92 i had an uncontrollable miss. First it was only when i would hot start the car, But over time, it turned into a full fledged issue.

I took it to my mechanic who tried replacing the ECU, tried plugs and wires, tried timing, tried just about everything. We were thinking is was massive wiring issues. Until i ran a can of injector cleaner, and the problem got a little better, then worse.

Long story short, I had 2 injectors that would trade off when they wanted to work. So i would check those definitely. Also make sure you're getting necessary fuel. Like, no clogged filters or kinked return lines. Then check wiring, if that stuff isn't the issue.

 

[snox135]

I would say both of your problems are coming from the ecu. If you have one you can swap i would try that. Other wise call up the place that repaired your ecu and see if they can verify that everything is working. If you installed the chip are you sure that all of the prongs are seated correctly?

 

[staticbrainwash]

I installed DSMlink myself, but the cap replacement and socketing was performed by Steve so I trust that the work was done properly. As for the datalogger, it was just some ebay cheapy that worked fine before I had to rebuild the engine. I sent my laptop and harness to Thomas at ECM tuning to have it checked and everything was working fine, so the problem lies somewhere in my car.

I doubt it's the ECU if the socketing and everything was done by the Steve (who i assume is from DSMlink).

Check injectors and fuel, but maybe it's just a communication issue with dsmlink in general that is throwing everything off.

PS, Are you still trying to run the GMmas with the maft? Or are you running it off of the DSMlink? There could be a communication issue there too.

 

[larsrya8]

I would take this to the DSMLink forums. Tom and Dave will be able to help you diagnose any ECU problems.

 

[GVR4592]

When you say COP, are you refferring to coil on plug? If you have coil on plug have you ever had the car run correctly with it?

What all did you change when this started happening? Was it just the engine? Was there anything electronic that you changed? Like the COP, Maf-t, ecu/dsmlink, etc?

 

[staticbrainwash]

I brought up the DSMlink and maft combo for a reason. I know DSMlink can run a GMMAS, so if he still has his MAFT plugged in i believe there could be some issues.

 

[snox135]

The reason I'm thinking there is a ecu problem is because he said the factory scan tool won't talk to it either.

Have you tried reinstalling the factory chip?

 

[Marc91GSX]

When you say COP, are you refferring to coil on plug? If you have coil on plug have you ever had the car run correctly with it?

What all did you change when this started happening? Was it just the engine? Was there anything electronic that you changed? Like the COP, Maf-t, ecu/dsmlink, etc?

Yes I have coil on plug on the car, but I put that on in hopes that it was a coil pack problem. This problem first occured after the install of the engine. After the engine was installed and this problem first occured we thought it was a bad ground situation so I replaced all of the grounds on the car. After that I have tried to diagnose this problem and failed. Here is a step by step of everything I have done and why I have done it.

1) missfire happened on initial startup so I replaced grounds ( they were 15 years old and I should have done that anyways)
2) missfire still there so I borrowed a known good cas to check if that was the problem.
3) missfire still there but I found out that one of my injectors was bad so I replaced it with all I had ( the 750s I bought for a larger turbo after break in)
4) car was running very rich so I had to install the 90 model eprom ecu and dsm link just to get it to idle right ( according to my wideband idle is 13.1 under boost is 10.3, rich but manageable)
5) performed a comp test and noticed the numbers were low in all cylinders but still within spec ( low was 130ish and high was 140ish cold)
6) changed plugs and gap
7) checked resistance in coil pack, it was bad so I replaced it with another stock coil pack that tested good.
8) I had to return that coil pack to my friend because he got his car on the road and since I like the looks of a COP setup I chose that instead of a stock replacement.
9) I have replaced the power transistor as well

Through out this entire time I have checked the timing belt to ensure that it is still in time (paranoid) and adjusted the base timing atleast 10 times trying to find a setting that worked.

Now here are some ideas that my friend has suggested to me that I am curious about. He has said that there is a possibillity that my lash adjusters could be bad, I have weak valve springs, or the install height on the valves is too high. Does anybody think that my missfire could be a result of those problems

 

[Marc91GSX]

The reason I'm thinking there is a ecu problem is because he said the factory scan tool won't talk to it either.

Have you tried reinstalling the factory chip?

No I have not installed the factory chip back in the ecu but I have had the same problem with the 91 ecu that came in the car. As for trying to get help from Thomas and Dave they are also at their wits end about the communication problem. I have been PMing them since I got dsmlink. If the problem is in the ECU then howcome I am getting the same exact problem in both ECUs ( factory one, then eprom one while factory was being rebuilt, then the factory again, then the rebuilt eprom with dsmlink)WTF WTF

 

[larsrya8]

I brought up the DSMlink and maft combo for a reason. I know DSMlink can run a GMMAS, so if he still has his MAFT plugged in i believe there could be some issues.

Just for the record, DSMLink still needs the GM MAF Translator to operate. It doesn't have native GM MAF support yet.

As for not working with either ECU... maybe there is something wrong with your communication port or your ECU wiring harness. Check for shorts or missing pins. Now that I reread and saw that this happened after an engine install, I strongly believe that this could very well be a wiring problem.

 

[snox135]

No I have not installed the factory chip back in the ecu but I have had the same problem with the 91 ecu that came in the car. As for trying to get help from Thomas and Dave they are also at their wits end about the communication problem. I have been PMing them since I got dsmlink. If the problem is in the ECU then howcome I am getting the same exact problem in both ECUs ( factory one, then eprom one while factory was being rebuilt, then the factory again, then the rebuilt eprom with dsmlink)WTF WTF

Sorry, I must have missed that you had tried two diffrent ecu's.

 

[snox135]

Was dsmlink set up for 750's?

 

[Marc91GSX]

Just for the record, DSMLink still needs the GM MAF Translator to operate. It doesn't have native GM MAF support yet.

As for not working with either ECU... maybe there is something wrong with your communication port or your ECU wiring harness. Check for shorts or missing pins. Now that I reread and saw that this happened after an engine install, I strongly believe that this could very well be a wiring problem.

I also have thought that I have a wiring problem, I have just not been able to find it. Every time I have changed ecu's I have checked the wiring from the port to the ecu and also checked to verify that all pins are in the proper location and tight.

 

[Marc91GSX]

Was dsmlink set up for 750's?

yes it was and as soon as I installed it I reset the MAFT back to stock 450s so that there will not be a mix up between it and DSMlink.

 

[larsrya8]

yes it was and as soon as I installed it I reset the MAFT back to stock 450s so that there will not be a mix up between it and DSMlink.

You will still need to "calibrate" the MAF with the airflow sliders in DSMLink, but the car *should* still run fairly well. Did you check any of the wiring under the hood?

 

[Marc91GSX]

You will still need to "calibrate" the MAF with the airflow sliders in DSMLink, but the car *should* still run fairly well. Did you check any of the wiring under the hood?

None of the exposed wires are damaged, but I have not started stripping off the loom over the harness to check there. If I can't get this resolved soon I will strip off the loom and check the wires there as well.

 

[Marc91GSX]

I was wondering if there is anybody near me that has a 1g turbo car that would be willing to hook up my ecu with dsm link installed in it to see if a communication can be made with the ecu. If I can speak to the ecu in their car then I know that it is a wiring issue in mine and it will help me to narrow down the problem.

 

[Marc91GSX]

Well I am tired of this stupid car so I am going to part her out. Keep an eye out in the classifieds section or PM me if there is anything you want. Thanks to everyone who responded to this post, I appreciate your help. The problem is beyond my abillities to fix and I am tired of sinking money into this car.