5.7-89GTA

SOLVED. Thank you to those who posted suggestions and pointed me to ignition as a possibility. I swapped in a standard replacement coil ($12.48) and the car revs hard to the redline under load. Been busy with other stuff and could not get to this until today (9/13/2021). I don't remember what brand coil I put in the car in 2009, but I think it was supposedly a higher performance type. No markings on it except "Made in USA" on the bottom. New coil is likely imported, but for now it is working.

I hope someone can point me in the right direction here. Been having a recurring problem with my 1989 GTA L98. In a previous post I suspected a fuel pressure problem, but after test driving with a gage attached to the fuel rail and monitoring the FP it seemed to be in spec. The car will not rev over 3500 rpm, either driving in gear or revving in neutral. It acts like a plugged cat, but the cats have been deleted. Not to bore anyone by directing them to my previous post, the cliff notes are: about 8 years ago replaced FP, filter, wires, plugs, rotor, cap, ignition module, coil. This year I replaced injectors with stock replacement from FIC. FPR diaphragm also replaced along with MAF and O2 sensor. No apparent vacuum leaks. Car starts and idles good and has power up to the 3500 rpm wall. Today I checked the TPS voltage. .54 dcv at idle position, 4.32 vdc at WOT. Is that too low at WOT? I researched other posts and found one where the OP replaced the EGR and FPR cover and that solved a similar problem. Would/could the EGR be a cause? Also, no SES light or codes.

Thanks for reading.

aliceempire

iTrader: (14)

It's over 4volts so I wouldn't be overly concerned. It's only a 5volt reference.
The egr shouldn't be the problem. If it's hooked up correctly, the egr is only commanded to open during cruise speeds. If the egr is opened all the time then it wouldn't idle well at all. If it's closed all the time then it wouldn't have any running effect, just a check engine light. You can easily test the egr by capping the vacuum ports and try it.
As long as there is no air restriction on the intake and no restriction on the exhaust, then either you're losing fuel or losing spark.

afgun

When did the problem start? Before you did the tuneup 8 years ago, after, or just recently?

5.7-89GTA

This is recent. And sporadic. When I was suspecting the fuel pressure and testing the car with a gage attached I could not reproduce the problem. Thought it somehow "fixed itself". Car sat for a few weeks and problem is occurring again. Fresh fuel.

wlink14

As aliceempire said, you are either losing fuel or spark, but the question here is why. Faulty sensor giving you a bad reading which is causing improper fuel/spark? Crank sensor? Just thinking out loud here...
Can you explain the 3500 rpm "wall" more thoroughly?

5.7-89GTA

The engine just will not rev past that point and if i let up on the throttle slightly and let the engine rpm drop a little it has "normal" power. If you have ever experienced a vehicle with a clogged cat, it acts like that. But my twin cats are gone and there is no exhaust restriction. I agree that there may be some signal that is causing the ecm to either kill spark or fuel. Short of throwing parts at it, my diagnostic skills are limited.

afgun

I feel that this is an ignition/voltage issue. If your voltage remains fine at 3000 RPMs then I'd go after the coil or ignition module. I realize you changed them, but newer ignition modules have a reputation for being, well, junk... if you have your old ones, you might try swapping them back in one at a time unless you know for a fact they're bad.

wlink14

You should be able to test the crank and knock sensors with an ohm meter. I am also pointing fingers at the aftermarket ignition stuff, but eliminate some other variables first.

aliceempire

iTrader: (14)

There is no such thing as a crank sensor for these. The closest thing is the distributor and yes that could have something to do with it.

Whitebird75

Have you checked your base ignition timing? What is it set at?

QwkTrip

iTrader: (22)

Usually lack of fuel would result in gradual stumbling as fuel flow rate is increased, not a dead wall with no warning. And engine likely would still free rev easily (uses little fuel to free rev).

Loss of spark can cause a dead wall though.