NE1 mess w/ C4 Vettes?

[Chuck Leeper]

We have a 90 L98 engine Vette.
Customer says no start. He then screws w/ putting in a new dist module, and tries to set the initial timing at 6*..No dice. can't get the 6*. Calls us, gets it running well enuf to drive it over.
We have another new module, new PCM/memcal, installed.
The dist cap was rotated into the back of the plenum, so we backed the shaft up 2 teeth, disconnected the EST wire, and set the ignition at 6*. Plugged the EST back in.. NO start. Twisted the dist to get max timing, Starts but runs poorly. Moved the dist again, to smooth out the idle.
Cannot accelerate the engine off idle. Got the code 42.
Dumped the code, by disc the batt. Unhooked the EST, fired up. Plugged the EST back in. Ok til the next start cycle.
This is a speed density car, so no excessive sensor inputs to mess with. TPS is set to .54, per GM spec.

NE1 have a clue as to where to start?

 

[Street Lethal]

Chuck, I'm running a '90 Speed Density LB9. Just to confirm, the engine does not start, and when it does start, it idles and runs horrible with the EST connected. However, when you disconnect the EST it starts okay and holds a somewhat decent idle, but once you plug the EST back in it will repeat all over again when you shut the engine and restart it, is this correct?

 

[TexasT]

balancer spun?

 

[Chuck Leeper]

Chuck, I'm running a '90 Speed Density LB9. Just to confirm, the engine does not start, and when it does start, it idles and runs horrible with the EST connected. However, when you disconnect the EST it starts okay and holds a somewhat decent idle, but once you plug the EST back in it will repeat all over again when you shut the engine and restart it, is this correct?

Yep. We have tried all kinds of positions on the distributor. We see 18-19* on the scanner.
My bud has worked on these cars for 30 yrs, and is at a loss. Between the 2 of us we are stumped.

 

[Chuck Leeper]

balancer spun?

I'm wondering the same thing.
After I posted, we got it running, showing 18*, but can't find the marks w/ a timing light. U can crank the timing lite from 0, to all the way over 50*, and can't see the marks.
We set the 6* using a dial back light. Next I am going to jack it up, and get to the balancer, turn the engine w/ the flex plate, use a tdc whistle, And see WTF is with the balancer.
The car has 115K on it, is all original.
I've been doing this for near 75 yrs, and it's kicking my ass. Most likely, something that's staring us in the face.

Thanks for the input, guys.
Damn! I need a nap....

 

[TexasT]

Bring it to tdc on the compression stroke and see where the mark on the balancer is.

Opps, I see you are going to try that.

 

[Street Lethal]

Yep. We have tried all kinds of positions on the distributor. We see 18-19* on the scanner. My bud has worked on these cars for 30 yrs, and is at a loss. Between the 2 of us we are stumped.

If it's starting and idling in Alpha-N with just the TPS and RPM data, but then acting up when the EST bypass is reconnected for Open Loop, double check that the 1 Bar MAP sensor is reading the correct values at key on, as well as the IAT/MAT sensor. These two sensors could throw the fueling completely off if they are failing and giving values that are skewed, while not triggering an SES light. Since it does run in Alpha-N, this kinda eliminates the possibility of it being fuel related, but it never hurts to check to see if the engine is still running the stock Multec injectors because they are notorious for shorting out, and just one bad one will short them all out. The balancer can definitely be the problem as well...

 

[Chuck Leeper]

If it's starting and idling in Alpha-N with just the TPS and RPM data, but then acting up when the EST bypass is reconnected for Open Loop, double check that the 1 Bar MAP sensor is reading the correct values at key on, as well as the IAT/MAT sensor. These two sensors could throw the fueling completely off if they are failing and giving values that are skewed, while not triggering an SES light. Since it does run in Alpha-N, this kinda eliminates the possibility of it being fuel related, but it never hurts to check to see if the engine is still running the stock Multec injectors because they are notorious for shorting out, and just one bad one will short them all out. The balancer can definitely be the problem as well...

I checked the MAP. Good.
IAT appears to read accurately. Reads ambient at cold start, rises as the manifold/engine heats up.
Injs are "new".
I'm zeroing in on the balancer, next.
Thanks!

 

[ITSAV6]

My son had a 91 C4 and it would act wonky at times. It would be rich as heck and other times be weak kneed. The map sensor worked but was off 20% or so and the coolant temp sensor was reading temps below zero at 70deg temp and 250+ at 170 deg. The china ign module and coil were crap too. Replaced the 2 sensors and ran way better, put Delco module and adapt a cap and MSD external coil and it was a new car.

 

[Chuck Leeper]

and the coolant temp sensor was reading temps below zero at 70deg temp and 250+ at 170 deg.

We have found this, on this car. We then plugged in another sensor, and it read ambient. Fans didn't work, as the sensor didn't get hat enuf.
Next, the new sensor is going in, along w/ the balancer inspection.

Thanks for the input!

 

[ITSAV6]

check the ign module also, it wasn't working right either

 

[seedling]

What was the fix if you don’t mind me asking?


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[Chuck Leeper]

What was the fix if you don’t mind me asking?


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We have put the car at the bottom of the to do list. Customer is not interested in getting it back, anytime soon.

 

[Pronto]

We worked on one that turned out to have a replacement egr that was loose and wired backwards. Ran like shit and after it ran great.