ImBatman

I know several of you have followed my past threads and have been very helpful. Unfortunately everything I have checked and tried has failed to fix the issue. Here is what it is doing and what I have done

Problem:
The car will crank if it sits for a long time. Once it does crank it will run fairly smooth for sometimes an hour sometimes only a few minutes before it dies.
Once it dies I may get it to crank again by pressing the pedal to the floor and just continue spinning the starter. MOST times what happens is it will attempt to start, almost start, backfire but nothing.
After it sits for a long time and I mean at least 24 hours it usually starts but does the same thing!

Codes:
It has an H41 and a couple of other history codes stating communications faults but those seem to be related to windows interior lights but nothing that appears engive or computer failures related to the engine.

What I have done:
-Performed a fuel pressure check at the rail. Rail pressurizes to 41 PSI and even after 24 hours it holds around 27 psi.
NOID check for all injectors
Smell test on the fuel regulator for gas. No smell or raw fuel

Replaced:
-fuel pump including sock
-filter
-cap
-rotor
-icm
-coil
-wires
-plugs
-MAP sensor

What I have not done:
-emptied the tank. Gas is about 6 months old but the car runs fine for an hour or more or sometimes 10 to 15 minutes.
-Fuel pressure regulator. The rail psi would rule that out wouldn't it?

What am I missing!?!?!?! HELP!!!!

About to take it to a shop but want it running when I pull in and not get stuck with a tow bill.

Thanks
Wade

antfarmer2

have you tried to put a cold pack on the ecm to see what happens? or clean and check the connectors?
I would also recheck the coil and icm and make sure you used the proper thermal grease.

Kevova

What are all the codes in all the modules. Communication codes can cause no starts. Corroded grounds, connectors in poor condition due to over probing where terminals are spread, Connector weather seals missing. Intermittent pick up coil / pole piece can cause no starts, usually won't set codes.

ImBatman

-The ECM never gets hot when I have the car idling in the driveway with the hood up.

-I have done the 'jiggle' check on the ECM connectors but did not find anything

-I did use the grease contained in the ICM. Not saying this couldn't be the problem again but the fact that it will run at various time intervals makes me think that it is something else.

-I will get all of the codes again this evening and post.

- How would I check this? still makes me wonder why the car will run and drive but for various intervals of time. 'Intermittent pick up coil / pole piece can cause no starts, usually won't set codes.'

**One thing to clarify between the 2 different scenario's when the car does run.
-For the short intervals the car shuts off essentially because it is so cold natured. So once it cuts off it may or may not restart.

-For the longer duration test drives you can come home and again sometimes it will crank back up but most times no. During the time it does crank up you can come back 20 minutes later and it want...

antfarmer2

have you tried the smack test? while it's running smack the ecm and see if it dies I have seen reports where the solder connections crack and need to be redone.

ImBatman

hmmmm, interesting and might be therapeutic too! I will try that tonight!

Kevova

Do you have a Factory Service Manual or alldata?

Vic'89

Please ohm out all the fuel injectors both when they are hot and also cold.

Vic

Tom400CFI

on the injectors.

Also, when it does stall out, what is missing that prevents it from running: SPARK or FUEL? When it dies, check.

woody41

I had issues with my 91, if you still have the original exhaust check your cat convertors there are 3. I ended up having to get mine towed to a Corvette shop where they did a back flow test, one of the pre-cats had completely collapsed and the other was barely flowing. My would start and die as soon as you touched throttle and not restart unless it sat overnight then same issue. Worth a check...

Magnus Kaas Meinild

This.

You need to find out what condition is causing the problem.

But I do find a fuel pressure of 27 PSI extremely suspicious. That's not much over half normal pressure. Do you have severe vacuum in the tank when this problem occurs? Try unscrewing the cap after running the car for a good while or until it dies. It'll give a damn good hiss if this is the case.

27 PSI is about 36 % less fuel at the same pulse width. Your ECM will compensate for this up until a point, by increasing BLM's. But the ECM will stop at a certain point when BLM's hit the ceiling of 160.

If you do have a problem with vacuum build-up in your tank, this explains why the condition come creeping slowly. You won't notice it until the BLM is maxed and only after that, the AFR will start to lean out as you go. The backfiring fits pretty nicely too, as a lean condition can cause backfiring. The way it will go back to normal after a long night, also seems to fit with vacuum build-up. Seem's likely that a vacuum will slowly goes away on it's own.

Could be a fuel pressure regulator problem too. I'd say replace it. Preferrably with an adjustable regulator.

Wish you luck. It's such a shame to hear a fellow C4 owner loosing hope. TBH I find them pretty reliable and easy to work on, but too many C4's weren't properly cared for by previous owners.

Also if you invest in an ALDL cable with a 10k resistor, you can datalog and diagnose your condition more reliably. Look up moates.net

ImBatman

Thanks guys!
-For the spark and fuel it does have both after it dies but won't start.

-The fuel pressure only falls gradually over night and levels out at about 27. My understanding is that this is normal for the pressure to bleed down some when sitting a period of time not running.

-When the car starts the psi stays so where in the 38 to 41 psi range. This is at idle. I have not been able to monitor it going down the road.

-I have not done an ohm check on each injector but will.

-for the CATS is there a way I can check for one being collapsed at home?

Tom400CFI

Copy that. More likely injectors then.

That is fine. What is important is the pressure when the symptom occurs.

Seems pretty normal

Yes, hook a vacuum gauge to manifold vacuum. Start engine and monitor vacuum. At idle, reading should be ~18-20". It should stay that high. If it tapers off while idling at a consistent speed, that is an indication of a clogged exhaust. If it doesn't taper at idle, bring RPM up to ~2000, and hold. Again, vacuum should remain stable as long as that RPM is stable. If it tapers off, again, a sign of clogged exhaust.

Another way is to tap into your exhaust ahead of all cats, and measure exhaust pressure.

Cliff Harris

Don't ever connect a 10K resistor to a Corvette. It does the following (as described in the FSM):

Closed loop timers are bypassed
EST (spark) is advanced
IAC will control engine idle to 1000 RPM
On some engines canister purge solenoid will be enabled
Park/Neutral restrict functions will be disabled

Stephenms

I had a similar issue in a 1991 Z28 I had. It would start right up in the mornings, run decently for almost 30 minutes but then start to die, sputter and kill itself. Once I tried to restart I would get absolutely nothing. Just the starter working its *** off only to never give fire. Turns out I had rust in my gas tank that would clog the fuel pump strainer once the pump warmed up and moved enough fuel. I threw hundreds at the car trying to figure it out. Replaced the gas tank and new fuel and the issue never showed its ugly face again.

I hope you figure it out

Magnus Kaas Meinild

Just to clarify on data logging:

Older ECM's needs to briefly see 10k ohms over the A,B connectors in order to start sending data.

This is not true for all years, and I do not know if your 91 needs this or not.

On an ALDL cable from moates the resistor is a small switch, so you can get the data going and then turn it off again.

As Cliff said it's not a good idea to run the engine with the resistor on/in place. But you only need it in place for less than 30 secs for the data to start flowing, and this can be before you start the engine. Just need ignition on.

PS. All of the settings Cliff mentions can be changed in ECM with the proper chip programming and tuning software, but this is a whole different topic.

aklim

Give Jon at FIC a call and get yourself a set of reman Bosch III. According to THIS article, you have Multecs and they belong in the trash can. I would have them cleaned and tested every few years.

Ohm test is a poor man's test that isn't very helpful, IMO. All you have is that the coils are good which is a part of the equation. That leads you to go chase other gremlins ASSUMING that the injectors are good. Only good way I can think of is to bench test them. That way, you can see that the flow pattern and volume (none of which can be ohm tested) is good. Personally I am never certain why people don't choose to have the injectors tested every few years other than it is a hassle and cost. OTOH, because injector failure is so gradual, it is impossible to really "feel" it in the SOTP dyno and you get used to the running condition till it is really FUBAR. Exactly why I send mine out every few years. The "before and after" tests do show improvement after the cleaning.

Vic'89

While I do agree with you that Injectors should be cleaned every few years, the chances of all 8 injectors being clogged and causing a No-Start condition is very rare.

I have seen 1 or 2 shorted out Injectors causing both banks to not fire, this will cause a No-Start condition.

Vic

aklim

True but he does have Multecs which do belong in the trash can. Why waste any other effort on them? Ethanol in our gas today wasn't in the minds of the Multec designers and has been said to eat at the coil windings which are cooled by the ethanol laced fuel