Engine Shuts off on acelleration

[RD in SD]

09 Corvette with heavy modifications including a Harrop Hurricane 8 throttle body intake manifold making about 700 HP. It is running a speed density tune. It was running fine after many many hours of modifications to the tune to get the car dialed in. Then it started backfiring and or hesitating on acceleration, then it started missing, then dying under hard acceleration, Now it is missing and dying under light acceleration and it is almost not drivable. There are no codes other than a MAF code which it has always had but does not set the light. During this time from running good to not running good I have changed nothing in the tune just been trying to trouble shoot it. The problem was intermittent and at times it would run fine now it is all the time. It shuts off, I loose all communications with the computer, it will only restart after I turn it off and restart it.

I have replaced spark plugs, injectors, crank sensor, o2 sensors and now the computer. I have tried multiple troubleshooting ideas and nothing seems to work. Does anyone have any new ideas?

[Woodchukka]

If you are losing communications with the ECM is it losing power? Have you tried power and ground connections to ECM, battery, chassis or alternator? Do you have a log of the poor running up until it shuts off and can you post it?

[RD in SD]

If you are losing communications with the ECM is it losing power? Have you tried power and ground connections to ECM, battery, chassis or alternator? Do you have a log of the poor running up until it shuts off and can you post it?

I agree that it appears to be loosing power and or ground. We did monitor it with the MODIS and I believe my mechanic said that power was good and so was ground. I can double check that stuff, how do I check for those things with EFI Live? We have checked all the battery connections and the grounds to the engine. What would the alternator have to do with it? The logs look normal it just looks like someone turned the car off when it dies. I am willing to log it again. What should I be monitoring?

[Woodchukka]

I read into your post that your issues started after you were off the dyno for a period? I know on my VY there is a ground connection hidden under the ABS module which has caused people trouble. Anything like that on the Corvette? I suggested the alternator as I have came across occasions where an erratic feed and a lower output from the alternator has caused problems generally with other things like lights being on putting a greater demand on the electrical system.

You should be able to log the vehicles voltage through efilive. Maybe before it cuts out the voltage might be erratic and then drop out. Makes me think is a wiring connection (or broken wire) as it occurs when I would see the engine has a lot of movement going in and now has developed further occurring a lower RPM however the engine is still moving. I would log engine sensors and voltage looking for erratic signals. I had an intermittent shift fault with trans of wife's car and it ended up being a switch and logging parameters is how I found it.

Oh you have said you replaced the plug however what about the leads? Now I think I had similar fault on my VY Commodore and it was a crack in the lead. It would only jump when the engine was under higher load and developed quite quickly into being undrivable. This fault occurred right after a "spirited" drive.

[RD in SD]

I read into your post that your issues started after you were off the dyno for a period? I know on my VY there is a ground connection hidden under the ABS module which has caused people trouble. Anything like that on the Corvette? I suggested the alternator as I have came across occasions where an erratic feed and a lower output from the alternator has caused problems generally with other things like lights being on putting a greater demand on the electrical system.

You should be able to log the vehicles voltage through efilive. Maybe before it cuts out the voltage might be erratic and then drop out. Makes me think is a wiring connection (or broken wire) as it occurs when I would see the engine has a lot of movement going in and now has developed further occurring a lower RPM however the engine is still moving. I would log engine sensors and voltage looking for erratic signals. I had an intermittent shift fault with trans of wife's car and it ended up being a switch and logging parameters is how I found it.

Oh you have said you replaced the plug however what about the leads? Now I think I had similar fault on my VY Commodore and it was a crack in the lead. It would only jump when the engine was under higher load and developed quite quickly into being undrivable. This fault occurred right after a "spirited" drive.

OK that gives me a few more things to check. I will give it a shot.

[joecar]

Using a DMM measure the voltage drops across any connections...

e.g.
- battery to starter,
- battery to alternator,
- battery to chassis ground,
- battery to engine grounds,
- etc...

Is the battery hold-down loose...?

Does it show the problem at idle...?

Have you checked all plumbing for leaks...?

Are injectors all firing...?
Are spark plugs all firing...?

Is this with the ECM that previously was not responding/communicating and now communicates (from your other thread)...?

[RD in SD]

Using a DMM measure the voltage drops across any connections...

e.g.
- battery to starter,
- battery to alternator,
- battery to chassis ground,
- battery to engine grounds,
- etc...

Is the battery hold-down loose...?

Does it show the problem at idle...?

Have you checked all plumbing for leaks...?

Are injectors all firing...?
Are spark plugs all firing...?

Is this with the ECM that previously was not responding/communicating and now communicates (from your other thread)...?

I will check all the connections tomorrow.

No problem at idle.

What plumbing, you mean air intake? It's a speed density tune now.

Yes all injectors are firing and all spark plugs are too. However I believe the are intermittently not firing but I cannot narrow it down to one cylinder on the miss. I have checked exhaust temp, pulled coil wires and pulled injector wires and I cannot isolate it to one cylinder.

Yes the new ECM has the exact same symptoms as the old ECM only I have been unable to re learn the crank sensor because the engine dies in the process each time.

[joecar]

I will check all the connections tomorrow.Check voltage drops with power applied.


What plumbing, you mean air intake? It's a speed density tune now.Any external air plumbing, including PCV hoses/tubes.

[Woodchukka]

Yes all injectors are firing and all spark plugs are too. However I believe the are intermittently not firing but I cannot narrow it down to one cylinder on the miss. I have checked exhaust temp, pulled coil wires and pulled injector wires and I cannot isolate it to one cylinder.

I picked the side that I had the miss on using the NBO2 sensors. When it would miss the voltages changed. Swapped leads from one side to the other and the changes I saw in the NBO2's changed sides as well so that narrowed it down to what was causing the fault as only swapped the leads over.

[RD in SD]

I wanted to thank everyone for their input. After many hours of troubleshooting it turned out to be the main engine ground above the starter was loose causing an intermittent ground this was shutting off the computer.

[joecar]

Glad you found it :cheers: