jwolves

hello my name is john i'm new to this forum i have a 1991 corvette took it out for a drive the night before last it was running great no problems at all all of the sudden my check engine light came on and the car shut down tried to start it and it would not start had it towed home thought it might have been the fuel pump tested it and it is good have fuel all the way too the rail but my injectors are not working if i put fuel in the throttle body the car starts and runs till the gas runs out checked the fuses and they seem to be fine it seems like the injectors are not getting any power has anyone had this happen to them is there a relay some where if there is can you tell me where it is at thankyou

Frizlefrak

Dear God....Vanna, can I buy a period?

John....first off, welcome to the forum, and we will do our best to help you diagnose and repair your car, but PLEASE, for the love of God, use some punctuation, will ya? Your car may not run on, but your sentences certainly do. I don't mean to be the grammar ****, but that gave me a migraine. I'm not asking literary perfection, just some grade school grammar.

Now...enough chastising. You stated the following...

How exactly did you test the fuel pump? Should I assume you put a gauge on the schrader valve on the fuel rail? If so, how many pounds of fuel pressure did you have? You would need around 38-44 psi for the car to run correctly.

Answer that, and we will go from there. If you have fuel pressure, the next thing we will do is test your injectors for power, and if the ECM is grounding them. We will also pull the codes out of the ECM and see what type of distress signal it sent before it conceded the battle. Given that you got a check engine light, I suspect something may have gone awry with your ECM or ignition / emissions system, but I want to rule out fuel pressure as the culprit first.

Again, I apologize if I sounded like an ***, but your post was quite difficult to read. Help me read your posts and I will help you fix your car. Deal?

bdw18_123

I don't know why, but that made me laugh my *** off!!

At least he used one apostrophe!

jwolves

the fuel presure is 40 psi. tested the wires on the injector for power and both wires are lighting up. when i put a test light on them. it seemed to me that it powered the injector up. and when i tried to start it. it fired up but shut down. to me it sound like the ecm is not grounding the injectors. if so how do i repair that? i ckecked the ecm for any codes and it did not come up with any codes. but i was on the highway and it was night time so i had my 4 ways on and the hood up for about 3 hours. and i was about 40 miles from home and the tow truck driver did not turn the 4 ways off on the ride home. that killed the battery completely. so that might be why the ecm didn't bring up any codes

cumbercr

When you tested the injector harnesses (I assume you were cranking the engine), did the test light flicker or stay on solid?

jwolves

the light flickered. why do you ask? i have a question!are both wires on the injectors suppose to have power going to them when the ignition is on the on position ?

cumbercr

Whenever the ignition is on, there will power to the harness. One of the injector wires is hot, the other is ground. The flicker indicates the ECM is opening and closing the ground path.

engle1147

If you have pulses your OK....the ECM and pickup coil are working...you may want to check the resistances of the injector coils with an ohm meter......you may have some of those OEM non ethenol compliant injectors in there. You can have a "pluse" without having the injectors actually "open" to spray fuel......I've seen first hand.

Short answer: The ECM needs to see the reference pulses from the distributor's pickup coil to have injector driver circut toggle to ground to complete the loop. Your seems to be working from what you described with seeing a "pulse"....off hand if I remember right - with the key in "run" engine "off" and/or not being cranked 12V should be present if measuring voltage from any (coil within the injector is connecting both sides of the injector's harness plug) injector conductor to a grounding point.



Here is a 92-93 injection circuit which nearly identical to a 91... which might help with understanding the voltage is present thing:

aminnich

Go to Autozone and buy or rent a noid light. Retest the injectors and let us know what you are seeing. Having power to both wires makes no sense so maybe a noid light will clarify what is going on with the injectors.

cumbercr

If he grounded his test light to a different ground, he will see power on both wires. The test needs to be done across the two injector connector terminals with the engine cranking. The fact he got a flicker tells me his injectors are likely pulsing correctly.

Frizlefrak

It makes perfect sense. Run the route of the internal portion of the injector in your head. Power comes in one side, runs through the coils internally, and comes out where? Correct, the other terminal. The ECM does the grounding, not the injector.

Correct.

Soooo....let's run the scenario here.

1. 40 psi of fuel pressure on the rail.
2. ECM grounding (pulsing) the injectors (in theory, noid light will verify).
3. Car will run momentarily when fuel is introduced into the intake.
4. ECM threw a code, but it has since been wiped clean.

So gentlemen, where should we be looking? Why would the ECM pulse the injectors now, but stopped doing it (in theory) when the car was running down the highway? And if you have fuel pressure and injector pulse now, why won't it start now?

Let's go back to my triangle.

1. The correct mixture of fuel and air.
2. Suitable compression.
3. A suitably strong spark delivered at the correct time.

Which of these has suddenly become deficient, and why? If the car will start and run momentarily with starting fluid down the TB, that automatically rules out numbers two and three. No compression, spark strength, or ignition or valve timing issues.

Now....what would cause the ECM to not give us #1? The check engine light was our clue.....I have a couple of theories, but first, I want to verify with the noid light that the ECM is in fact pulsing the injectors. And what if, say for example, the ECM is pulsing the injectors, but just not allowing any fuel to flow? The dead battery eliminated the cry for help, but not the symptom.

Now...correct me if I'm wrong, but a 1991 is a TPI car, and they are batch fire, correct? Have the injectors on both banks of the engine been tested, or just one injector? Will the engine start and run if, say for example, only 4 injectors are firing?

Here's something else to test if we run out of other ideas....the TPS. What if the ECM thinks the TPS is at WOT when he's cranking it? (hint...clear flood mode). And while were on the subject of the ECM, is it getting a 12 code now?

Toss out your ideas gents....this can't anything terribly difficult.

engle1147

If he's already got spark, air, proper fuel pressure and injector pluses but still no fuel (as he indicates as he throws fuel into the intake manually that it runs) To me this clearly seems to be a fuel delivery problem. I recommend getting some new type III injectors installed in there. Talk to Jon with FIC he's thee supporting fuel injector vendor here.

zzpw3x

If it was running fine before the incident, and it won't start now, the only way the injectors can be the problem is if you lost several injectors all at the same time.

That is very unlikely.

I am at work and the circuit diagram is blocked so I can't see it. If the ECM pulls the low side of the injector directly to ground, then it should have no voltage at all. The light should not pulse on the low side. If the path to ground is lost, that would explain why there is voltage on the low side of the injector. If there is a pull down resistor (on the low side of the injector) in the ECM before ground, then it will have voltage and the light should pulse.

cumbercr

I vote for a test of the TPS. Very easy to do. If that tests well, I would look next at the mass air sensor.

aminnich

[QUOTE=Frizlefrak;1571458973]It makes perfect sense. Run the route of the internal portion of the injector in your head. Power comes in one side, runs through the coils internally, and comes out where? Correct, the other terminal. The ECM does the grounding, not the injector.
QUOTE]

I was assuming he unplugged the injectors, so the wire from the ECM should not have any power thru it. Is it possible that he has an injector with an internal short causing feedback thru the ground side?? That is a question, not a statement.

jaa1992

Andy's suggestion is one of the scenarios a master vette mechanic was thinking was my problem on the 92. One of the injectors could have a dead short or open and can cause the one bank not to pulse. In my case it was not looking closely at the fuse panel and looking at the correct fuses.
On my 92 the IN1 fuse was blown.
With that knowledge in the back of my head and a comment from Gordon Killebrew from many years ago about the ECM fuse I would go back to the fuse panel with all new fuses and replace the ECM, IN1 and IN2 fuses.

Be sure you check the injector pulses with a noid light. I got the kit from Autozone. Basically you pay for it and when you return it they give you your money back.

Ohm the injectors, since its not running you can only do it cold.

One more thing that comes to mind is grounds - don't know where they all are on the 91, should be spelled out int the FSM. Disconnect them, clean and reconnect them. C4's seem to have an aversion to bad grounds.

Frizlefrak

Ahh...yes, you are correct. If the plug is pulled from the injector, only one side should have power. Good point.

Let's go back to our original symptom. A sudden engine loss of power and a no-start condition, preceded by a check engine light. The ECM knew something was amiss, but has been unfortunately saddled with amnesia due to the dead battery. That will complicate things. Without that distress signal, we're just going to have to run tests.

But what all this tells me is that we have an EFI / emissions issue....ie....a sensor out of spec, an open circuit, or a catastrophic ECM failure. Let's start with the basics....both INJ fuses should be tested for continuity, as should the ECM fuse. Resistance should be measured on each injector. A noid light should be used on each injector. Voltage should measured throughout the range of the TPS.

Now....what else will cause the ECM to not send a signal to pulse the injectors? In fact, where does it get that signal from??

engle1147

Not really since S128 & S131 (splice points) can back feed the other end of the harness/injector sockets through the coils in the rest of the injectors on that bank...all the injector connections on each injector for each side of the bank would need to be pulled for only one side of the injector bank for only one leg of the connector to not have power. I feel the OP's current issue is a injector fuel delivery issue myself....from what I have read so far.

josephf31

a fuse that controls the injectors? May not be labeled as such but I seem to remember...there is one for the fuel pump, have you checked them all?

jwolves

ok i just went outside to go to autozone to rent the noid light. popped the hood took the charger off the battery and turned the engine to make sure the battery had charged. well the car started up and is right now sitting at idle in my driveway. hit the gas a couple of times and it's running like nothing ever happened. no check engine light or anything. but i'm scared to take it out for a drive. what if the same thing happens again. what do you guys think ?