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Fuel pump prime on engine shut down?

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Old 10-10-2018, 10:21 AM
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Fuel pump prime on engine shut down?

I've done a tiny bit of PROM tuning lately ('165 6E), trying to nail down the AE and idle mixture, but no major changes.

The other night, I shut the vehicle off after moving it to the garage, and I heard the fuel pump running. No idea if it was continuing to run, or started when I turned the vehicle off...this pump (Delco) is a lot quieter than the Delco it replaced. Anyway, it ran just like the key on/engine off fuel pump prime cycle, I heard the pressure build up, then the pump shut off.

I did some research, all I can find are people who have had bad relays or oil pressure switches that stuck, but those were all about the pump continuing to run at certain times. This was definitely akin to the prime cycle. I was working in the garage on the vehicle for 15-30 minutes the next day, and it didn't randomly occur while I was there.

I've had .bins corrupted before that caused weird issues, anyone want to weigh in as to whether that might be the case here or not? Not in a position to restart it to test now, kind of in a time crunch to get some things done that don't allow the engine to be run, just curious if anyone thinks a .bin corruption is likely, or something else I've not considered.
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Old 10-10-2018, 11:14 AM
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Re: Fuel pump prime on engine shut down?

I would try to check power on the relays green/white wire. Sounds like it could be the ecm not the new .bin
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Old 10-10-2018, 11:16 AM
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Re: Fuel pump prime on engine shut down?

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Old 10-10-2018, 11:20 AM
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Re: Fuel pump prime on engine shut down?

For testing here is a cheap 165 ecm
https://www.thirdgen.org/forums/engi...ome-other.html
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Old 10-10-2018, 11:49 AM
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Re: Fuel pump prime on engine shut down?

I've got spares.

Actually have the ECM loose anyway, I can always swap it.

I know I need to figure out if it repeats, but even if I can't, the one time is enough to need fixing. Something isn't right. If it starts randomly doing it, I'm going to end up with a dead battery. Vehicle sits for long periods, a load like that will toast the battery if it keeps going on.
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Old 10-10-2018, 04:49 PM
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Re: Fuel pump prime on engine shut down?

A cold engine with cold oil will run the fuel pump for a short while after key-off. As it takes longer for the oil pressure to bleed off.

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Old 10-10-2018, 05:28 PM
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Re: Fuel pump prime on engine shut down?

Ahhh... that makes a lot of sense. It's a new gm crate, less than 3000 miles, and runs 45psi at idle...and it was cold.

I had considered that as it was happening, but since the gauges go dead , I had no idea what the pressure looked like. Use the later switch/sender combo, so it should reflect the pressure if its affecting the pump running.
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Old 10-10-2018, 06:06 PM
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Re: Fuel pump prime on engine shut down?

First time it happened to me, it was surprising. Only ran the engine for a short period of time, got out and could hear the fuel pump running. Oh-oh, then it stopped. Riiight... oil pressure switch which closes at about 4 psi. It was also cold that day to make the oil thick.

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Old 10-11-2018, 11:55 AM
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Re: Fuel pump prime on engine shut down?

I just noticed this last night on a quick start then shut down to swap chips, glad I saw this probably ran for about 6 to 10 seconds after shut down and it was in the 40's so this make sense.
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