Rough running

[Billy Mild]

Let me preface this post with the dilemma I'm in, daily driver Jeep CRD is out of commission due to a trusted out diesel tank, 2 motorcycles are out of service 1 with a seized engine and the other cosmetic issues, and now the Vette has decided to run a little rough.

On the highway the ZR1 seemed to almost fight against itself, but if I go full throttle the Lt5 pulls just fine. The car would buck or almost feel like it was going to die but if I have the car more throttle it would pull without hesitation.

It is happening at low rpm sub 3000 RPM. Something that I also noticed is that the speedo quits working randomly.

Could this be a fuel pump problem? Spark plug issue?

Fuel injectors, coil packs, and wires have been replaced in the last 2 years. I have SW headers and new O2 sensors with a Marc Haibeck tuned chip.

Sent from my Nexus 6 using ZR-1 Net Registry mobile app

[BigJohn]

Originally Posted by Billy Mild

Let me preface this post with the dilemma I'm in, daily driver Jeep CRD is out of commission due to a trusted out diesel tank, 2 motorcycles are out of service 1 with a seized engine and the other cosmetic issues, and now the Vette has decided to run a little rough.

On the highway the ZR1 seemed to almost fight against itself, but if I go full throttle the Lt5 pulls just fine. The car would buck or almost feel like it was going to die but if I have the car more throttle it would pull without hesitation.

It is happening at low rpm sub 3000 RPM. Something that I also noticed is that the speedo quits working randomly.

Could this be a fuel pump problem? Spark plug issue?

Fuel injectors, coil packs, and wires have been replaced in the last 2 years. I have SW headers and new O2 sensors with a Marc Haibeck tuned chip.

Sent from my Nexus 6 using ZR-1 Net Registry mobile app

So I'm not the only one who has issues with multiple vehicles.

[8cam]

You might not like this answer, but those symptoms sound exactly like an ECM going out. I had similar issues and finally rolled the dice on a repair, which worked in my case. But sometimes they don't.

[Billy Mild]

Is there a ECU repair service? This was a common problem on the old 944's I had. There were a few places that actually re did all the solder joints, fixed the problem.

Did your car seem to pull clean for full throttle?

Sent from my Nexus 6 using ZR-1 Net Registry mobile app

[Billy Mild]

http://www.zr1.net/forum/showthread.php?t=25548

I found this old thread and they talk about having it rebuilt or a possible new option. Sounds like MegaSquirt makes a new ECM that is plug and play. I would like to figure out cost and if it has all the same functionality as stock now.

Sent from my Nexus 6 using ZR-1 Net Registry mobile app

[8cam]

I had mine repaired by K&B Corvette here in Atlanta. He said he had about a 2/3 success rate with them. I knew mine was tha culprit so I rolled the dice and the repair worked. Yes the symptoms were the same, rough idle and running. Part throttle acceleration was ok, full throttle was ok at first. Then it wasn't, and things just got worse. Definitely worth checking it out. I eliminated all other possibilities before I was certain it was the ECM, finally swapped in a known good one to confirm it.

[Billy Mild]

My idle seems okay. Not bad at all. Reving the engine while stopped seems fine as well.

What tests did you do?

Sent from my Nexus 6 using ZR-1 Net Registry mobile app

[Paul Workman]

It might well be the ECM, and you may be right. But, it sounds like a "closed loop" situation (to me).

Just a suggestion: B-4 throwing another part at it, or ASSUMING those parts you've recently replaced "can't possibly" be bad, do have it scanned and see what is going on before trying to second-guess it further. It might be something simple...or it could be the ECM. But, odds are it will be something else - like a connector?. Just sayin.

[Billy Mild]

Originally Posted by Paul Workman

It might well be the ECM, and you may be right. But, it sounds like a "closed loop" situation (to me).

Just a suggestion: B-4 throwing another part at it, or ASSUMING those parts you've recently replaced "can't possibly" be bad, do have it scanned and see what is going on before trying to second-guess it further. It might be something simple...or it could be the ECM. But, odds are it will be something else - like a connector?. Just sayin.

I'm all for testing. I already own a MT2500 scanner. I don't know what I would be doing to check the ECU.

I was thinking a possible fuel pump issue, but I don't have a fuel pressure gauge to test with. I may pick one up this weekend.

The car when it has this issue acts like my RZ350 when the carbs are out of sync. The cylinders run at different speeds and fight each other

Sent from my Nexus 6 using ZR-1 Net Registry mobile app

[8cam]

I have the shop manual and basically just started working through all the rough running tests. It's pretty comprehensive and gives you expected results throughout. After testing everything, the only item left for me was the ECM. I borrowed one from Russ and my car suddenly ran perfectly, so it was clear what the issue was. The guy at K&B isn't very sociable, but for me at least, the fix was great. He told me that they will all fail at some point, and with a 2/3 success rate on repairs, they will only keep getting more expensive. Hopefully your issue is something simple, but definitely start working through the shop manual.