Fuel pump intermittently does not work

JLKULESA

MEMBER
2004 CHEVROLET MALIBU
2.2L
4 CYL
2WD
AUTOMATIC
79,000 MILES

Fuel pump doesn't start up every time. Voltage at fuel pump relay on pin 85 is 12 sometimes and drops to 2 after 4 seconds. Next time key is turned on voltage is moving between 2 and 4 volts. When that happens if I move shift lever from park to reverse or drive and back to park the voltage will jump up to 12 for 4 seconds and back down to about 2 volts. From what I read on YouTube I'm thinking I might have a bad PCM. Don't know how to test it. Will be waiting for your input. Thank you. John.

Sunday, April 26th, 2020 AT 7:41 PM

3 Replies

ASEMASTER6371

MECHANIC
52,796 POSTS

Good morning,

The fuel pump will only run for 2 seconds with the key turned to the on position. That is a primer time for the system. The dark green/white wire is what comes from the ECM.

The voltage should be constant while cranking as when the ECM sees a tach signal from the crank sensor, it will turn on the fuel pump.I attached a diagram for you to view of the relay controls.

What is the issue with the car?

Roy

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Monday, April 27th, 2020 AT 4:20 AM

JLKULESA

MEMBER
3 POSTS

Roy,

The issue is the car does not start usually when it is warmer. If it is quiet outside I can hear when the fuel pump runs. As I explained before moving the shift lever once or twice will make the fuel pump run and the car starts up. Once in a while it will stall on the highway, I then move the lever to neutral, shut switch off, turn back and it starts and I go to drive and the car runs just fine. I've done that at 60 MPH more than once. Will be waiting for your reply. John

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Monday, April 27th, 2020 AT 10:54 AM

ASEMASTER6371

MECHANIC
52,796 POSTS

Okay, first, the pump can run but not produce enough pressure for the engine to run. Just because it runs does not mean it is okay.

The pressure needs to be tested to be sure it is putting out the correct pressure.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

The fuel pressure needs to be a minimum of 50 pounds. 55-60 is preferred.

Roy

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Monday, April 27th, 2020 AT 11:21 AM