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Engine intermittently and suddenly dies

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Old 06-14-2017, 03:02 PM   #21
C4ProjectCar
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After it dies and refuses to start, check for spark and injector pulse while cranking.

Injector resistance is a very vague test. That it seems good doesn't mean there isn't an issue which is why I never run those myself. It could short when hot which causes an issue but when testing, it doesn't show a thing. The pintle could be cut off and the coil is good and you would be given a false negative.

If you have a stock MEMCAL, why exactly do you have an emulator? Just because the connections are solid doesn't mean the electronic part cannot act up when hot.
It never refuses to start. It usually restarts on its own immediately, and the times it doesn't I am able to start it within a second or two of cranking as usual.

I tested the injectors just for kicks, but I never really suspected the injectors being a problem. For it to completely die, most likely all of the injectors would have to simultaneously stop working momentarily (right?). Also, other than when it cuts out it makes good power, and emissions were very good.

I do plan to hook a noid light up to an injector tonight and see what happens when the engine cuts out.

I have an emulator because I needed to tune for modifications and I opted to forgo the hassle of erasing and burning a chip every time I tweaked something. (The stock MEMCAL and the emulator both plug into an adapter that uses the tune from the emulator, but reverts to the MEMCAL if the emulator fails.)


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I don't think the ECM is that sophisticated.
If not, then how does it know when to reset those counters? The obvious answer would be when it sees the ignition switch go out of the "on" position, but that is clearly not happening in this case.


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Originally Posted by JimLentz View Post
Is the engine modified? If not, how does it run with just the MEMCAL? I am not sure about that ECM and the counts.
Yes, it is stroked to 383 and has new heads and cam. It's been a long time since I ran it with the stock MEMCAL, but I recall it runs pretty rough. I'll have to monitor the BLMs to make sure it isn't going too lean to correct, but you're right--reverting to the stock MEMCAL would be a good way to rule out the adapter and emulator.


EDIT:
I read that the reference signal to fire the injectors originates at the distributor. If this is the case, a fault in the distributor could cause loss of either spark or fuel, correct?

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Old 06-15-2017, 03:02 AM   #22
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I read that the reference signal to fire the injectors originates at the distributor. If this is the case, a fault in the distributor could cause loss of either spark or fuel, correct?
The ECM uses the DRPs (Distributor Reference Pulses) to synchronize the firing of the injectors to the rotation of the engine. The ECM also uses the DRPs to keep the fuel pump relay energized. As long as the engine is rotating, the oil pressure switch will also keep the fuel pump running.
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Old 06-16-2017, 10:40 PM   #23
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The ECM uses the DRPs (Distributor Reference Pulses) to synchronize the firing of the injectors to the rotation of the engine. The ECM also uses the DRPs to keep the fuel pump relay energized. As long as the engine is rotating, the oil pressure switch will also keep the fuel pump running.
So when I hook a noid light up to an injector, the noid light stopping wouldn't really be meaningful? E.g. a bad distributor could potentially skip a couple DRPs, or alternatively the ECM could be shutting off the injectors.

One thing I just noticed is that the CEL seems to flash twice in quick succession when it dies, it doesn't just blink once like I had previously thought. Blinking once makes sense since the CEL should be lit with key on, engine off, but I don't understand why it would flicker twice.
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Old 06-17-2017, 01:18 AM   #24
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It's the emulator! Took it for a drive with the stock chip in the socket, and it wouldn't die once. Swapped the emulator back in, and it died before I got out of the garage. Then back to the stock MEMCAL: it wouldn't die. I smacked, shook, and wiggled the Ostrich, its ribbon cable, and the adapter with the engine running, and none of that would make it die, yet something in that system undeniably is the cause of my problem.

What a relief to finally have this tracked down. Thank you to all you guys for helping me out and finally steering me to try that, can't believe I didn't try that months ago.

Any thoughts as to whether the emulator, ribbon cable (it's a little crimped from the lid on the ECM), or adapter?
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Old 06-17-2017, 05:07 AM   #25
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Great job. Got another emulator?
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Old 06-18-2017, 01:35 PM   #26
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Default I think you mentioned the problem...

The way your car quits it makes me think it is electrical.
You mentioned that the wires (Tach and the Pink wire) that have clips on them are broken. Those clips are very important as they hold those connectors snugly into the distributor, especially the pink one as it carries 12 volts to the distributor. It is very important to hold the wires in their respective sockets securely. Be sure that the connections are free from any corrosion as well.
If the pink wire is not tight you might be heating up the connection and causing it to pull more current because of the additional resistance.

Bad connections will haunt you for a long time unless you deal with them. Go buy yourself a replacement plug for the pink wire at least. Get a good solid connection there and see what happens. If you can't then secure it somehow so it stays tight in the socket on the distributor.

Inside the distributor there are other connections that might be shorting to ground and killing the engine. When I bought my car it looked like a five year old tried his hand at wiring. I have spent many hours fixing wiring mistakes made by someone who knew very little about electricity.

I wish you the best in solving your problems there!
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Old 06-19-2017, 01:54 AM   #27
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Great job. Got another emulator?
I wish. Shot Moates an email and I'm waiting to hear back from them.
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Old 07-06-2017, 08:36 PM   #28
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Well, it's fixed! I replaced the Ostrich with a regular ol' chip, and no more dying. I talked with another forum member who had a similar issue, and it sounds like the Ostrich just has issues when used on C4 ECMs from '90 onward.
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Old 07-07-2017, 12:32 PM   #29
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Wow! That was a tough problem to find. But your sharing it here helps us all. Congrats!

But you still need a tune for that 383". I confess I really don't know how the old school tuning work for the EPROM ECM's. I expect you need a chip burner with the correct software but don't know how you adjust the timing and mixture on the dyno to find max power when you have non-erasable data.

Meantime I recommend you don't go full throttle at all and keep RPM below 3,000.

Please let us know what you find that works.
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Old 07-07-2017, 03:25 PM   #30
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thank you for coming back with that update. Those are the kinds of little nuggets that will prevent others from months and months of troubleshooting in the future. Congrats on getting her up and running to your satisfaction.
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