I've got a 91 z28 with the 5.7. Cars pushing close to 190,000 miles. Problem started a few months ago. I could drive the car maybe 30 or 40 miles and then it would just die going down the highway. no bogging or fighting to run. Just flat dead. The car would then have to sit for an hour to hour and a half before it would restart and run. It would have to idle for awhile and if I snapped the throttle it would die again. Since then the problem has gotten progressively worse to the point that just sitting in my driveway it seems like if I look at the gas pedal it dies and won't restart. It will crank and crank and if it does catch it dies withinn seconds. I've checked the fuel pump, which is only a year old. You can hear it actuate and I've got 42-44 psi at the fuel rail. New fuel filter so I know it's not clogged. I've checked and replaced almost every sensor on the car. IAC motor, TPS sensor, MAP sensor, Ignition control module, etc. Even cleaned all the buildup out of the throttle body. I'm about to the point of thinking somethings wrong in the ECM even though it's not throwing any DTC's. Any help I can get on this problem will be greatly appreciated.

 

Sounds VERY MUCH like the ignition module.

In fact, if I were to write a textbook and want to describe what those do when they have heat failure, I could use your description word for word.

That's the little 7-pin thing inside the distributor, held down by 2 screws, with the heat sink grease under it. Is that what you changed? If not, try a new one. Don't bother with "testing", unless you test it while it's at 200° temp; just replace it. Don't forget of course, to put the white heat sink compound under it: not doing that will cause it to self-destruct very rapidly.

OTOH...sounds like fuel delivery.

What is the fuel pressure WHILE IT'S SCREWING UP; not, while it's sitting in the driveway idling; not, after it primes and before you start it; but, WHILE IT'S IN THE ACT OF MALFUNCTIONING? Tape your gauge to the windshield with duct tape if necessary, to find out.

Just because something has been replaced, doesn't necessarily mean that (a) it's good, (b) it's working right, or (c) there's not someting else keeping it from working right. So leave the whole "I just replaced it" idea out of your troubleshooting vocabulary, just put it out of your head altogether; and treat EVERY PART as a suspect, until you eliminate it from consideration by some other means involving observation and logic.

 

Brand new ignition module in the distributor. And the 42-44 psi on the fuel pressure at the rail was while trying to restart the engine, not while running. Went after the ignition module because I saw a flutter in the tach. Last time my ignition module went out the tach fluttered and went nuts but the car would not catch and run. With how bad the problemn has gotten I can't even get the car to run long enough to heat up. I will double check the fuel pressure tonight though just to make sure.

 

The ECM doesn't take control until the engine is turning at least 400 rpm.
So your problem is:
Fuel
Spark
Mechanical Timing
Air/Compression (minimum 80psi)

With an unkown vehicle, or one with known good spark, and fuel I first confirm mechanical timing.

As mentioned don't assume anything, but for now ignore fuel, and spark.

1.) Verify balancer timing mark is aligned with timing pointer, or zero mark on timing tab at #1 piston Dead Top Center, the key here is to first locate DTC mechanically with a piston stop inplace of the #1 spark plug. If the timing marks align properly then proceed to verify distributor alignment.

2.) After that is accomplished check compression with all plugs removed and throttle wide open, max psi should be reached in no more than 10 complete rotations per cylinder.

If mechanical timing and compression are good adding fuel, and spark should get it to start with zero timing at DTC.

Alwaya disconnect the ECM setting connector when setting initial timng.

 

If compression and/or timing were off, wouldn't that be a constant problem? The car will start after sitting for awhile and idle fine up to the moment I rev the engine, then it dies and fights to restart. If I don't touch the throttle it will start and idle fine. Or am I seeing things from the wrong point view?

 

that sure sounds like a good case of fuel pressure. Put a gauge on it, and rev itup. when it fumbles look at the fuel pressure. I'm willing to be that may be your problem, right there.

 

You have an engine that runs, but not all the time, or properly so, something is missing, correct? Now there may be someone who can tell you exactly what's wrong just by your symptoms, but I can't i have to take the long road.

No, you're not seeing it wrong, but it's better to know that there's enough compression, and correct mechanical timing. It's not the same to idle as it is to run under load. When you have a problem like this it pays to start with the basics. I do it because I can't tell by ear if an engine has sufficeint compression. The fact that the rotor lines up with the #1 spark plug on the compression stroke doesn't garrantee that the piston is at it's proper location, even if the engine does start, a few degrees off can make a big difference.

The first thing I do is disable fuel & spark proceed to timing then compression in that order. Finally add spark then fuel. I have yet to fail to start and run an engine under load doing it that way.

Godd luck - Raul

 

Congrats and welcome to the "runs when it wants to club"
Your issue is almost identical to what i am running into on my 87 5.7. my personal opinion is this is in the wiring someplace... which isnt that helpful of a statement, but if i had the answer i wouldnt be in the same boat.

 

Checked the timing last night. Ran at 6 btdc, which my chilton says is the correct setting for my engine. So I guess next step will be compression, which I'm not looking forward to since the plugs are a pain in the ***.

 

did you check the fuel pressure?

 

Start testing your wire harness from the coil to the ignition control module and make your way back to the ecm.

 

????

 

One of the first things I checked.

 

 

What might that be? Doesn't look familiar.

 

It's a pickup coil. Goes in the distributor.

When you checked it, was that WITH THE CAR DRIVING DOWN THE ROAD AND SCREWING UP; or was it sitting in the driveway idling and behaving normally?

Remember, we're not looking for just a "fuel pressure" problem; rather, a potential fuel DELIVERY problem.

 

That was sitting in the driveway watching the pressure when the car died.