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Fuel Pump / Starter - ECM control or direct wire??

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Old Aug 12, 2025 | 06:36 AM
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Default Fuel Pump / Starter - ECM control or direct wire??
Getting to the point where I'm looking at the final wiring on my swap. Putting a Gen3 LQ4 / 4L80e into a 1951 Pontiac. Are there any advantages to having the fuel pump and starter control wired through the ECM versus wiring everything direct and bypassing the ECM? What functions/features does the ECM provide that direct wiring would not??

Thanks for any advise!!
Cheers TM
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Old Aug 12, 2025 | 02:04 PM
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Fuel pump control is personal preference, i see no advantage having PCM control. The starter wire is not controlled by the PCM, it i usually wired to a starter relay
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Old Aug 12, 2025 | 07:16 PM
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I like PCM control for the fuel pump because it primes and shuts off. Running keyed power to the fuel pump relay keeps it running any time you are key on.
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Old Aug 12, 2025 | 07:53 PM
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On my LS swaps as said above I always control the fuel pump thru the ECM. Of course a fused relay in the harness is used. The ECM needs 12 volts all the time direct from the battery and 12 volts in start and run.
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Old Aug 12, 2025 | 09:20 PM
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Originally Posted by nleming
I like PCM control for the fuel pump because it primes and shuts off. Running keyed power to the fuel pump relay keeps it running any time you are key on.

The prime feature is the only benefit
If your pump does NOT have a built in check valve, it can be worthwhile to run continuously
Personally, I always use ECM control for the pump

Starter is always external. Typically, OEM starter relays are a part of the anti-theft system
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Old Aug 13, 2025 | 05:48 AM
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You want the fuel pump to shut off in a hard crash that stops the motor. A fuel pump that continues to pump fuel in a post crash situation is unsafe.

Rick
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Old Aug 13, 2025 | 07:29 AM
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Originally Posted by B52bombardier1
You want the fuel pump to shut off in a hard crash that stops the motor. A fuel pump that continues to pump fuel in a post crash situation is unsafe.

Rick
SOLD !!!! I simply hard wired it initially to get the motor running on the stand and just assumed I'd transfer that over to the car. But never thought about the possible consequences of it running continuous - not thinking specifically about a crash, but a fuel leak or anything. I wasnt aware it had a priming function and then need to see the motor running to operate.

Thanks all for the input!!!!

Cheers TM
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Old Aug 13, 2025 | 08:05 AM
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Originally Posted by B52bombardier1
You want the fuel pump to shut off in a hard crash that stops the motor. A fuel pump that continues to pump fuel in a post crash situation is unsafe.

Rick
Not all ECMs have this feature. Often pump shut down is a byproduct of a bad crash severing/destroying key electrical components or an external inertial switch

Since the OP did not state which controller he is using, we can only speak in general practice
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Old Aug 13, 2025 | 01:40 PM
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Originally Posted by Pocket
Not all ECMs have this feature. Often pump shut down is a byproduct of a bad crash severing/destroying key electrical components or an external inertial switch

Since the OP did not state which controller he is using, we can only speak in general practice

Its the stock unit from a 2005 Savanna 3500 with a 6.0ltr
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Old Aug 13, 2025 | 04:06 PM
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Stock GM ECM's if they don't see crank rotation it shuts down the fuel pump.
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