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No Power to Fuel Pump Relay

  • Lady2010
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1 year 11 months ago #63361 by Lady2010
No Power to Fuel Pump Relay was created by Lady2010
Hello, I'm working on a 1995 Chevy G20 Van 5.0L V8 TBI. When the van was towed to me it would run about 10 secs and shut off. Before I did any work on it I was able to get it to run at least 5 mins with the map unplugged before it would shut off. It ran like crap and black smoke was coming out the tailpipe. I was told it was smoking like that before the other problems started. It is a friend of mine's work van, and it needed a lot of TLC. I have the van running smooth and no more black smoke, you can drive it, but the problem I'm having now is power to the fuel pump through the relay. When the van came to me, they were using a relay with a piece of plastic tied around it to keep the contact closed. This fried the new fuel pump they had put in and killed the battery, because they didn't unplug it.

The wires on the relay are as follows: 85 Blk/Wht  86 Grn/Wht 30 Gray 87 Orn 87A Red. I have 3 relays one is GM, one from AutoZone, and one from O'Reilly's. I have checked all 3 and they test good. When I plug them up, I get the same thing on all of them. No click therefore no power to fuel pump. I have constant power on pin 87 and the ground is good on pin 85. When I crank the engine pin 86 has a very dim light with the test light, but I don't get anything on pin 30. I have tried to put straight power to pin 87A. It sparks a little, but the pump doesn't turn on. I have taken each pin out of the connector to make sure it is clean, not stretched, and the wire is intact. I have tried putting power to the gray wire still nothing, but when I jump pins 30 and 87 pump turns on and I can pull the jumper and the van will continue to run letting me know the oil pressure switch is good. I have tried putting power to pin 86 with a good relay plugged in to see if I could get it to click and it wouldn't. I have checked pin 86 at the ECU and the light is still dim. I have checked all wires at the connector for continuity.  Power and grounds to the ECU are good. All the fuses are good. I have tried everything I know and I'm at a dead end. Any other ideas are greatly appreciated.

So far, I have installed a new fuel pump, IAC, TPS, MAP, ECU, Oil pressure switch, ignition switch, plugs and wires, and both coolant temp sensors. Replaced battery, cleaned throttle, and new air filter. I was told when they installed the first fuel pump, they installed a new fuel filter as well.

The codes that come up are 34-Map sensor ( I have tested the new map sensor and it is within specs), 54-EGR system or fuel pump circuit low voltage. The EGR needs replacing because it wouldn't hold vacuum when I tested it.

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  • Tyler
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1 year 11 months ago #63368 by Tyler
Replied by Tyler on topic No Power to Fuel Pump Relay
I can see why you're at a dead end. This relay sounds like it should be working!

Since the pump runs with 30 and 87 jumped, let's focus on the control side. Take two voltage measurements, one at 85 and the other at 86, during the fuel pump prime or during cranking. Relay installed. I know you found a dim test light on 86 and a good ground on 85. But there has to be something missing. 

As an alternative, you can supply your own power AND ground to pin 86 and 85. Carefully, of course, so you don't ground out. With both jumpers installed, the relay has no excuses.

If the relay closes and the pump runs, remove the jumpers one at a time until the relay opens. If the relay still doesn't close, then either there's still something wrong with the relay and/or socket, or something wrong with the jumpers.
The following user(s) said Thank You: 00Jake00

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1 year 11 months ago #63478 by Lupe
Replied by Lupe on topic No Power to Fuel Pump Relay
THE control and ground have to be checked under load to get a good test . you might have a short from ignition . good luck

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