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Old 11-19-2004, 06:15 PM
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relay harness not getting power?

In tank elec fuel pump went bad, so I replaced it... while checking to make sure it was the fuel pump and not the relay that was bad, i pulled the relay off the harness, checked, and put it back on. I've installed the new pump, and the pump itself will turn on when 12v is applied to the terminals, but with the key turned in the 'on' position, the fuel pump relay harness is not getting power anymore. There are two power wires that go to the harness, I checked both, 0volts each. Why would the harness not be getting power? Wires are all good, no brittleness, they connect directly to the batt. but yet have no power, engine cranks fine, but fuel pump never comes on, fuel relay never clicks, harness never gets power. Checked every fuse in the fuse box, all fine.... Im lost...

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Old 11-19-2004, 09:35 PM
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Fuel Pump

Ok on most GM vehicles from 88 to 95 your fuel pump relay should be as follows:
1) orange wire is battery voltage thru the fuse box

2) red wire is for your fuel pump prime connector

3) Dark Green/White Fuel pump command from your PCM

4) Black/White Ground.

5) Grey wire runs to the tank unit but is spliced also into the oil pressure gauge.

Some V-6 engines had a in line 20amp fuse coming off the bulkhead connector that was were red turned to orange after the inline fuse.

On all GM's the fuel pump prime connector (red wire/black connector-should be on right side toward firewall) allows you to apply 12 volts direct to the fuel pump. If it runs then you have a fuse, Relay, or PCM bad. Key on, engine not running the orange wire should have 12volts. If it is not a blown fuse then it is a break in the circuit. If it is hot you need a Digital Volt meter to check voltage from the PCM the Dark Green/White wire. This is provided all grounds are good.
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Old 11-21-2004, 02:22 PM
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(86 btw) Right, have all those colors, 2 orange wires, 1 red, 1 black, 1 green/white, except for no grey. Fuel pump prime connector? Fuel pump relay is on the right side (driver) along with 3 other relays... the orange wires dont have any voltage.
However, I noticed, with the ignition on, im getting 8 volts to the rear connector to the fuel pump, with the relay connected or disconnected.

So you're saying IF the orange wire is hot to check the PCM wire for voltage? Any idea what that voltage should be aorund?

....Having a hard time finding this fuel pump prime connector....

Last edited by arch; 11-21-2004 at 02:29 PM.
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Old 11-22-2004, 03:58 AM
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8 volts

Doc here:

If your getting ONLY 8 volts at the pump, (under load? I assume) Check the ground, you may have forgot to hook it up when you replaced the pump. you need a hard frame ground from the tank in order for the pump to operate.

If it's just 8 volts without load (open wire testing) You have a bad connection or burned contact at the relay. Run a test lead directly to the pump and see if it runs.

If so, measure continuity from the pump wire to the relay plug, on R x1 scale it should read 0.00 ohms..higher readings or none at all, replace the wire.

If that's good, replace the relay. You probably have a burned contact..not unusual if the old pump went out..

Doc
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Old 11-22-2004, 05:57 AM
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update

Restore60s, I got your PM, (Been testing with digital multimeter) and from looking at a wiring diagram I've located the fuel pump prime connector, its a red wire that is part of the relay harness.
Last night I noticed my service engine light wont come on while in the 'on' position. Engine still sparking and cranking fine.
Bulb is good, havent found the source of that problem ethier, im hoping nothing happened with the ECM though. The two orange wires still have 0volts going to them. Hmm... while typing I was looking at the wiring diagram, and it shows "2.0 TAN/WHT SXL, .8 BLK/WHT GXL, .8 GRN DK/WHT GXL, .8 ORN GXL, 2.0 ORN GXL" going to the relay. However, In the circut listing, it says the .8 orange is the red pump prime feed. On the auctual harness I have green/black/red/orange/orange.
Im going to go out and check the ECM/engine light.
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Old 11-22-2004, 06:44 AM
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ECM

That might be your right direction finding out why no service engine soon light is on, even more so if the bulb is okay. I would verify 12v to the PCM. Do like Doc said and check grounds. As with most cars I don't think you have a wiring problem, just a component failure. If you have access to a scan tool that would help if to verify the PCM (ECM) data stream if it's working. The bulb on some early models is powered by a lamp driver module but yours being Fuel Injected should be right from the PCM. Should be Brown/White & Pink wiring. The first thing I used to do on no-start conditions on Computer Controlled Vehicles was to verify a working service engine soon light and if it was inop then as Doc said verify grounds, fuses and if they were okay to trouble shoot the Computer.
Was the car running before the pump was put in? And something that should have been asked before what kind of vehicle is it?
I'll check back with you this afternoon, have to go baby-sit the fisherman for a few hours.
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Old 11-22-2004, 08:08 AM
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finally

I pulled the ecm, Main power 12volts, secondary power 0volts. So I checked all the fuses in the fuse panel, all good. Checked the connections on the battery, all good, Pulled the wire loom apart by the battery, and there was a fuse hidden inside... pulled that, burnt out. Replaced, Boom fired right up. Damn fuses cause all the problems.... Ripped apart the dash, half the engine wiring harness, the ECM and the under side of the dash, for one damn fuse in the engine compartment...

Thanks again guys....
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Old 11-22-2004, 09:19 PM
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Don't you just love that hidden stuff. I was just troubleshooting a problem on my Cad. As least the shop manual was nice enough to tell me there was a splice 5 inches down the wiring harness.
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Old 11-22-2004, 10:54 PM
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Wiring....

Doc here:

More fun than an instant Insanity cube....with the spots changed..

General Mystery Wiring harness....

Like a children's easter hunt..."find as many components as you can and bring them back here"...

It's worse on a Vette...The book say's, and I quote: Some models Had it, some did not...may be located in the center console, or behind the glove-box...If not behind the right side kick panel".. On just about any electrical component you can think of!

Glad to hear ya got 'er fixed anyway!

Doc
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