89 stock vert
Car was running fine, put gas in it earlier in the day. On my way home last night it stumbled twice and died would not restart. Pulled a plug wire and checked for spark.. I have spark but will not start. Turns over fine just no start. So I tow it home. This morning I check FP 38lbs with key on and it started right up, 42 lbs running at idle.. Shut it off and after 30 min still have 40lbs of FP.... What can it be I dont want to take it out and get stranded somewhere. Fuel Filter? Cat going bad? Just a gremlin

 

It is always a good idea to check for stored trouble codes as a first step.

More than likely it is your stock fuel injectors as they are non ethanol compliant and ethanol blended gas is everywhere these days....'89 seems to be the worst year for non compliance issues....the fuel injector coil windings are effectively being "shorted out" so little or no fuel is making it into the cylinders.

If you can find nothing else "wrong" with the car/fuel delivery system replace all of your injectors with a ethanol compliant set.

 

The only way you're going to find the problem is to get it to die again. Keep you pressure gauge handy

 

Try squirting starting fluid in the throttle body and see if that starts it.

 

Any updates with your vette?

 

Here is the update....................
It started again the next morning, I took it to the store and on the way back it started bucking like it was starving for fuel, Put the gauge on and had 38 rail and 42 @ idle, Taped gauge to windshield and back out of the driveway, gave it gas and it bogged right down fp was 40+ as I tried to accelerate.
I pulled back in and for lack of nothing better to do changed the fuel filter, started back up pressure good but bogs down when you accelerate. Pulled back in the Driveway and it died and would not restart, have spark and fuel pressure, Showing 1 code "36"... Where do I look now?

 

You may have a bad injector. I had one go on me and the car completely died and wouldn't start again. Weird how just one injector can cause so much trouble!

 

This is a long shot but could it be water in your gas? This is the time of year when this happens the most and by what your discribing it sure sound like this could be the problem. You did say that you had just put gas in the car.. It wouldn't hurt to put a can of drygas in...WW

 

89 FSM

 

I was just going to mention the MAF burn off circuit but Mike beat me to it. I just looked up code 36 and here is what they list... (code 36 - Mass Air Flow (MAF) Sensor - burn off circuit problem) . This could be the problem unless its an old code...What this could cause is your maf sensor could have a dirty wire because your maf burn off is not working to clean it off. I would suggest first taking your maf sensor off and cleaning the inside with maf sensor cleaner..If this turns out to be the problem then you know your maf burn off relay is probably not working.The problem I have with this theory is if it were the maf sensor wire being dirty it should do it all the time, not every once in awhile.I have personally had a bad maf sensor on my car and it did buck and miss like your explaining but it was the maf sensor itself was bad, not the relay or a dirty wire....WW

 

Get a noid light and when it won't start, confirm that the injectors are being pulsed during cranking. Also, put a can of dry gas (alcohol) in your gas tank in case you do have water in your gas. Go through the MAF burnoff diagnosis that Mike posted.

 

A quick and dirty check - when it's Not starting, unplug the MAF and try it again. IF it then starts and idles (it may or may not Run all that well, but it Will at least Run), then the MAF is the problem. Why the MAF is bad then becomes the question. That's when the code 36 diagnostics come into play.

A "noid" light check of the injector pulse is OK, but 99% of the time if you have spark you will also have injectors. The EST circuit input to the ECM causes the ECM to both fire (provide ground) for the injectors And trigger the ignition coil. They happen "together". Unlikely that you will have spark and no injectors. Anything Can happen, of course, but..

I am also going to suggest another long shot. Not fuel related (a coincidence??), but the ignition coil itself. If this is a heat related thing, it Might be a dying secondary ignition coil.

These years have only the single O2 (lambda) sensor on the drivers side of the motor. I've seen cases where something will be wrong on that bank of cylinders (injector stuck "on", bad plug wire, etc.) causing a rich situation there and resulting in the ECM basically shutting off fuel to the whole motor. I've also seen the opposite - where a "full rich" cylinder on the passenger side of the motor has filled the muffler (true dual system with no crossover and no cat) with raw gas - and the ECM has no idea that anything is wrong...

The only way (well -the Easiest way) to diagnose That sort of thing is with a full-blown scope - something that shows you what's happening on a cylinder-by-cylinder basis. Sort of a shame that OBD-2 diagnostics weren't developed in time to have That capability on these years

 

Well it's not the MAF or relay (friend pulled his off same problem but no code), It started again this morning and when you accelerate it bogs and stalls. Now it wont start until it sits for a while. How can I check the ignition? ICM getting hot?

 

If it is heat causing the ICM to fail, your car should run perfect for about 5 minutes before ICM failure from heat, which usually kills the engine.

Does it run any differently in open loop vs. closed loop?

 

With Mike on the ICM..The coil can also do this, run good until hot then start missing..WW

 

It is running bad as soon as it starts, push the gas and it bogs and stalls... It's not running long enough now to get to closed loop.
Clogged Cat?

 

Pull the individual fuel injector harness connector clips off of all 8 fuel injectors (after the car dies out).

Have a DVM - Fluke style meter handy. Set it to to the OHMS scale.

Test each injector for resistance, should be 12 - 16 Ohms each.

If any or more than 1 injector reads below 12 Ohms- it is suspect-defective.

Your L-98 TPI engine is a Batch Fire System.

One bank of injectors all fire at the same time. 4 injectors wired in Parallel.

12 divided 4 = 3 Ohms. What the ECM quad driver transistors typically see for a resistance- current load in normal operation.

Any injector(s) with a low resistance reading will cause the ECM quad driver transistors to be overloaded- heat up rapidly.

The quad drivers shut down. The fuel injectors wont turn on when commanded by the ECM.

Your car dies.

Very possible that is what is occurring in your Corvette.

Alcohol additives slowly ruin the enamel insulation on the copper coil windings inside of each "GM MULTEC" Fuel Injector. The windings short out inside. Go out of resistance specs.

 

You can Impedance Test(resistance check) each fuel injector before your Corvette dies out again too.

Dont have to wait for it die out.

Usually when the GM Multec (1989-1996) fuel injectors are defective, the Impedance reading of each wont be different if they are cold or hot after running in the engine.

Good luck troubleshooting.

Let us know what you find wrong.

BR

 

I recently had the same problem until it wouldn’t start at all. Turned out the pick up coil went out or had shorted wiring. Knowing I was going to need a small cap distributor I replaced the entire dizzy rather then the pick coil. She fired right up and purred like a kitten.

Engle147 gave me these instructions to test the pick up coil.
You can test the pickup coil by putting a meter (set on Ohms) across the 2 wires coming directly from the pickup coil (unplug the connector from the ICM first), then spinning the distributor gear (remove the dizzy assembly from engine and spin by hand or leave in the car and use the starter to crank the engine) while watching the meter at the same time. If the pickup coil is doing its job you should see the meter readings swing from "higher" to "lower" resistance during the testing.

 

Your ignition pickup coil test(s) are correct.

But this Vette owner has ignition spark already. Never lost ignition spark. What he reports to us anyways.