No fuel pump voltage?

DAVID DANIELS2

MEMBER
1993 CHEVROLET SUBURBAN
5.7L
V8
4WD
AUTOMATIC
200,000 MILES

Working on a neighbor's car. After replacing spark plugs as well as cap and rotor noticed there was no fuel pulse when I tried to start. Disconnected the supply fuel line and it was bone dry. I suspected the fuel pump relay or fuse. I ohmed the fuse and it was good, replaced relay with known good with no change to symptoms. On the relay connector I get 12v at pins D and E. I suspect the oil pressure switch based on the diagram but not 100%.

5 Replies

JACOBANDNICKOLAS

MECHANIC
109,700 POSTS

At the relay, are you getting continuity to ground on the other two wires? Also, the oil pressure switch wouldn't cause it not to prime. If the fuel pump relay fails, it is backed up by the oil pressure switch, which continues to operate the fuel pump as long as the oil pressure remains above 28.0 kPa (4 PSI). However, it has nothing to do with a two-second prime when the key is first turned on.

Have you checked for power at the fuel pump?

Let me know.

Joe

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Friday, August 26th, 2022 AT 6:26 PM

DAVID DANIELS2

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4 POSTS

Not sure where this wire goes, but I found it tapped to a ground wire but not spliced.

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Saturday, August 27th, 2022 AT 9:13 AM

DAVID DANIELS2

MEMBER
4 POSTS

Have ground at black with white tracer, orange is short to ground with key off and clears with key on showing 12v. No voltage present on any other wire. No voltage at fuel pump at all.

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Saturday, August 27th, 2022 AT 9:18 AM

DAVID DANIELS2

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4 POSTS

Orange and green with white tracer are showing short. Which if I'm looking at the proper diagram both go to ECM.

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Saturday, August 27th, 2022 AT 9:21 AM

JACOBANDNICKOLAS

MECHANIC
109,700 POSTS

Hi,

The orange wire runs between the ignition switch to the ECM with the relay in the middle. That should have 12v when the key is on.

The green/white is the trigger wire from the ECM to the primary side of the relay. That is the power supply that actuates the relay to send power. Are you getting a signal on that wire when you turn the key on? If not, go directly to the ECM and check for power to that wire.

I attached the manufacturer's wiring schematic below for you to reference.

There will be either a solid black or a black wire with a white tracer for ground. Check that for continuity to ground.

Let me know.

Joe

See pic below.

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