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Author Topic: A warm engine is a dead engine  (Read 352 times)

Offline Desert Patina

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A warm engine is a dead engine
« on: 10:09:30 AM / 03-Sep-20 »
So thanks for the help so far. We are back to our original problem where the engine cuts out when it warms up. It can take 3-5 minutes, but the engine dies completely and we can no longer get spark or fuel signal for another 10-30 minutes.

We've swapped ECU's, distributor, and recently changed the temp sensor (the one that connects to the ECU). We also swapped the control solenoid for the EGR.

Any ideas?

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Offline Wonderingraven

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Re: A warm engine is a dead engine
« Reply #1 on: 10:13:22 AM / 03-Sep-20 »
What is the fuel pressure like?
It sounds like this one time my fuel pump would just die after a minute of working, the fuel pressure I watched from I believe it was 37psi to 10/15psi and wouldn't recover unless I let it sit for awhile.
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Offline Desert Patina

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Re: A warm engine is a dead engine
« Reply #2 on: 01:34:32 PM / 03-Sep-20 »
We did recently replace the fuel pump. But we are having problems with the circuit. The previous owner (I think the BaT post mentions this) bypassed the ECU and used their own fuel pump switch, we wired it back but we aren't sure we connected the ground / ground shielding correctly. It has a shraeder valve installed to watch the fuel pressure, we can try that.

Offline Wonderingraven

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Re: A warm engine is a dead engine
« Reply #3 on: 02:12:56 PM / 03-Sep-20 »
ahhh, wire gremlins.
hmmm! I would investigate there for sure and move up.
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Offline Desert Patina

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Re: A warm engine is a dead engine
« Reply #4 on: 06:59:52 PM / 04-Sep-20 »
Correction, the fuel injector signal is the only thing lost.

We checked at the ECU even, no "ground" is happening through the ECU when it doesn't work.

However, there is a spark (Tested with a timing light).

Fuel pressure is fine.

Offline Wonderingraven

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Re: A warm engine is a dead engine
« Reply #5 on: 07:16:09 PM / 04-Sep-20 »
ahhhh wire gremlins!
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Offline Desert Patina

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Re: A warm engine is a dead engine
« Reply #6 on: 10:26:53 PM / 04-Sep-20 »
Oh and just because it was asked ... the fuel pressure goes down after the engine cuts out. It can maintain 30PSI pretty easily (up to 35PSI when it first primes) but after the engine cuts out it falls.

I assume that implicates the ECU wiring if the Fuel Injector signal and the fuel pump cut off at the same time.

If so, I'm wondering about the EFI resistor. We mangled the old one, and soldered in a new 2.2 (2.4?) K resistor of what we thought was suitable power. But this is AZ, and it is hot, and I wonder if we chose the wrong resistor.

Anyone know where I can get a true replacement?
« Last Edit: 10:33:21 PM / 04-Sep-20 by Desert Patina »

Offline Desert Patina

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Re: A warm engine is a dead engine
« Reply #7 on: 08:57:15 AM / 08-Sep-20 »
Just as an update, this seems to be tied to a voltage drop ... measured at the battery terminal. When the voltage at the battery terminals drops to low 11 volts (and can go as low as 8 volts) the engine stalls. The ECU seems to drop the voltage to the pump about 20% (the FCM notes this behavior), so at the pump we see 8-6 volts which turns off the pump. It can get so bad that when restarting the starter only clicks.

Then ... mysteriously ... it recovers and we return to 12.4 volts at the terminal.

I don't see the 13v+ at the terminals that I should when the engine is running, but if I check from the alternator directly it is at 13.5 volts. So I'm suspicious of the alternator, and specifically the rectifier or voltage regulator.

Offline BOSSMAN

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Re: A warm engine is a dead engine
« Reply #8 on: 02:35:35 PM / 08-Sep-20 »
While you're at it check the alternator belt tension, ff the temperature gets warm the belt maybe loose.  If you can get new belts but don't get the expensive "gold" , top line belts because they will not break but they will stretch till you can't adjust.
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Offline weitrhino

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Re: A warm engine is a dead engine
« Reply #9 on: 06:12:49 PM / 08-Sep-20 »
As I noted on facebook, the Hitachi alternators are suspect at best and the Mitsubishis aren't much better. If you do swap the alternator, hunt down a Bosch and never sweat over it again.

Offline Desert Patina

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Re: A warm engine is a dead engine
« Reply #10 on: 12:29:48 PM / 09-Sep-20 »
We tested the Alternator and it passed all of Autozone's tests.

However, with the alternator removed, we do not see any voltage fluctuation at all at the battery terminals (except perhaps a slow drain).

The problem we suspect isn't a loss of amps or voltage being generated, but the rectifier or diodes may be failing or otherwise causing short conditions which drops the battery voltage temporarily and randomly.

Honestly I don't know a circuit which could have such an impact on the battery except the alternator, or perhaps issues within the battery itself. We'll try running it longer without the alternator and see if we see any fluctuation.

BTW, what is the part number for the Bosch alternator? If it is a matter of finding one that works but we need to change the pulley, I don't mind doing that.

Offline weitrhino

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Re: A warm engine is a dead engine
« Reply #11 on: 03:50:02 PM / 09-Sep-20 »
Bosch AL244X

Offline Desert Patina

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Re: A warm engine is a dead engine
« Reply #12 on: 05:32:23 PM / 14-Sep-20 »
It was the alternator. The car ran fine for 4 hours straight after replacing.

Offline rednucleus

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Re: A warm engine is a dead engine
« Reply #13 on: 08:19:16 PM / 14-Sep-20 »
Electricity is just weird how it screws things up so many different ways

Offline weitrhino

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Re: A warm engine is a dead engine
« Reply #14 on: 03:51:05 PM / 15-Sep-20 »
Clearly sounds like the voltage regulator inside had gone flakey. Glad you found a fix. Did you also find a Bosch?

Offline Desert Patina

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Re: A warm engine is a dead engine
« Reply #15 on: 08:11:18 AM / 16-Sep-20 »
We have the AC-Delco unit for now, but we will keep looking.