mmccoy940

Ok so this isn't even my car unfortunately I am not a corvette owner.
I am trying to help my friend though and am posting this for him. It originally start about a year ago. After the car was drove for about an hour it would just shut off after it set for about 5 minutes it would start back up and run fine again. It went on like that for about a month. Then one day it wouldn't start back. Before I started helping him he already put a new fuel pump and filter a new ecm a new maf and I think that's about it. It will run on ether, and if the car sits for about 10 minutes it will catch and almost start then just die. It has good fuel pressure at the rail, and the noid light blinked on each injector. Also it is not throwing any codes. So anybody got any ideas? What should we test next or look for? Thank y'all for your time and help.
-Matt

Cliff Harris

Check the ignition module in the distributor. It should have THERMAL grease under it, NOT dielectric grease. They get REALLY hot and fail. Come to think of it, they sometimes just fail, period. Take it apart, clean everything up and put new THERMAL grease under the module. If you buy a new module it should come with the correct grease.

A friend of mine had a similar problem (ran fine cold, died when hot) and it turned out to be a bad connection at the terminals of the ignition coil (in the cap of the distributor). The connector pins are crimped onto the wires from the coil and one of them was loose. He soldered all the terminals and hasn't had a problem since.

joe paco

it's always the same routines to locate the root cause: either spark, or air/fuel delivered in the proper ratio. no start can be no fuel, or rich fuel. if in jectors blink, probably ecm is firing them ok.

check for a strong blue spark first. an intermittent spark is No spark.

if TPI engines have one inj leaking, it can foul several plugs during start. also pull vac line from fuel pressure regulator to see if fuel comes out, indicating a leak.

if you suspect it is over-rich, try the throttle open while cranking. just looking for clues at this point.

mmccoy940

He said it has a new ignition module already, but I'll check and see what kind of grease he used if any. It has a strong blue spark we already checked for that. Ill check the fuel pressure regulator this evening. We've tried starting it with the throttle in every position possible the only way it gets close to starting is leave it sit for ten minutes don't touch the gas and turn it over it'll start for just a second and die.

Frizlefrak

You need to run the diagnostics during a no-start event. What you're describing is indicative of an ignition system problem. Any parts store can test the module, and as mentioned above, ensure the base is clean and has a THIN coating of thermal grease under it.

When it won't start, tell us exactly how many psi of fuel pressure you have, and if you have spark (use a tester).

mmccoy940

Well the car will not start at all right now so everything is a no start event right? And it had 45 Pei of fuel pressure and as soon as I get off we can take the ignition module to get tested. What would I use to test spark besides grounding it and watching the spark?

Frizlefrak

You can buy an inline spark tester at any parts store. They're under $10 at Harbor Freight.

mmccoy940

Well it passed the inline spark test and the ignition module passed at advanced. I feel like it has to be fuel related if it will start on ether. Any more ideas?

Frizlefrak

Yes.

When you turn the key on (without cranking), do you get the 2 second fuel pump prime and full fuel pressure? If so, how long does it hold? What I'm looking for is a failed fuel pump relay, and weak oil pressure switch (secondary path). If the relay is failed and it isn't developing sufficient oil pressure during cranking to activate the secondary path, it won't start.....but spraying ether in causes it to run momentarily and build enough oil pressure to keep the secondary path closed, and thus the fuel pump energized.

You mentioned you get injector pulses....is this when cranking during a no-start event? I want to see if the TPS is shorted and you're in "clear flood" mode.

Frizlefrak

One more thing....when it's in a no-start event, put it in diagnostic mode (jump A & B on the ALDL) and tell me if you're getting a 12 code. You may have a failing ECM.

mmccoy940

We get code 12 over and over again. It holds like 45 psi of fuel pressure and according to the dash the oil pressure is over 4. We did find out the fuel pressure regulator is bad and we will replace it tomorrow. Could that cause all these symptoms?

AGENT 86

89 was known for failing injectors. Ohm test each one and post the #'s.

Quick test to see if they are doing any real injection, is to hook up your fuel pressure gauge, prime the rail, remove fuel pump fuse and crank the engine.
If they are injecting, your fuel pressure will pulse it's way down to no pressure.

joe paco

I mentioned removing vac line from FPR to see if there was a leak. is that what you did? how did you discover a bad FPR if not? if it leaks inside, the extra fuel goes into the engine, causing an over rich condition, hard start, etc. if it holds 45 it does not sound like a leaking regulator, because it would leak pressure to 0 over a few minutes, flooding the engine.
if vac line is leaking, you may have the problem right there.

if you have a blinking node light it means ecm is operating injectors. but one of the several sensors tell it what the A/F ratio should be. if you unplug one, it will go to default, either to another sensor or to ecm memory.

try unplugging TPS. if no reaction, connect it, and unplug MAF. not sure if it should be using the 02 sensor right after shutoff, but if it is this will force the ecm to use another sensor, if I understand it correctly.

Frizlefrak

Now we're getting somewhere.

mmccoy940

Ill definitely try the ohm test and see if hold pressure with the fuse out. I pulled the vacuum line of the fpr and it smelled like pure gas indicateing the diaphragm is tore right? Ill try unplugging different sensors also and see if it changes anything. Thanks for all the help so far.

AGENT 86

Very possible. Do you have a hand held vacuum pump to see if the diaphragm will hold vacuum ?
If not, your fuel pressure gauge should notice a drop after rail prime and you may see gas exit reg nipple.

mmccoy940

Ok finally got a chance to mess with it today. It will not hold fuel pressure after it primes. If we clamp off the return line it will hold pressure. So that means the fpr is bad right? That don't make sense though because the fore is brand new.any suggestions anything to try?

vetteoz

Correct
Will it start up with line ( until it fires ) clamped to hold the pressure ?

mmccoy940

Sorry I hate autocorrect. The fpr is brand new. But it will not start even with the return clamped.

mmccoy940

Anybody? And I believe its the return its the rear right fuel line