1994 Chevy Suburban fuel relay wont work

Tiny
ALASKALOGGER34
  • MEMBER
  • 1994 CHEVROLET SUBURBAN
  • V8
  • 2WD
  • AUTOMATIC
  • 15,600 MILES
I have replaced my fuel relay plug and relay because my truck wont prime through the relay. If I jump the orange wire to the gray the pump will come on fine but if I hit the key nothing happens. It was intermittent at first but now it just wont prime. There is a green/whte wire and a red wire and a black/whte wire one needs to send a signal to the pump relay to prime and activate but its not, what do I do next?
Thursday, January 14th, 2010 AT 1:45 PM

9 Replies

Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Welcome to the forum, with the engine cranking, use a digital multimeter, check for voltage at the green wire with white tracer. At key on, no crank, that circuit should be hot for a few seconds.

Are there any trouble codes?
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Thursday, January 14th, 2010 AT 1:57 PM
Tiny
ALASKALOGGER34
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  • 6 POSTS
When I test the green and white wire it starts at.01 vlts and when I hit the key it only goes to.6 to.12 vlts and yes it is set at the right setting. Thanx for the help by the way there isnt a real mechanic in alaska i'm starting to think. I am at my wits end with this what could I do next. I was told there is no computer testing for this year is that true?
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Friday, January 15th, 2010 AT 12:28 PM
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
That reading should be battery voltage. There will be a difference between key on, and cranking, regarding battery voltage.

I'd check the pin at the computer connector for voltage, engine cranking, dark green wire with white tracer. Pin F6-- if good voltage there and not at the relay, problem with the wiring circuit.


https://www.2carpros.com/forum/automotive_pictures/170934_94_chevy_sub_1.jpg

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Friday, January 15th, 2010 AT 1:17 PM
Tiny
ALASKALOGGER34
  • MEMBER
  • 6 POSTS
This seems very strange but here we go! I unplugged the puter and tested the green/w #6 on blue clip and got no dif. In reading however with the plug out the pump came back on. I then plugged the puter back in and it is working again when I crank it.
However the grn/w wire still say's.02 in the on position during prime, and.15 during crank but the pump is coming on. Now it seems im not getting fuel out the injectors even if you pump the pettle as you crank and hear the pump on.
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Friday, January 15th, 2010 AT 3:10 PM
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Hi, I would have left the connector plugged in and back-probed the wire in question. Our database, MOD, says battery voltage on that circuit. The databases are not always correct. There is an oil pressure switch in your fuel pump circuit, parallel circuit to the relay. Once you crank it enough to bring up oil pressure, if there is voltage at the op switch and the switch is function, the pump will get voltage from the op switch and the pump will run, even with the relay unplugged.

If a problem with dark green wire with white tracer, you will not get an initial prime. With an extended crank, the oil pressure comes up, the op switch in the fuel pump closes and the pump will run.
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Friday, January 15th, 2010 AT 4:27 PM
Tiny
ALASKALOGGER34
  • MEMBER
  • 6 POSTS
I guess im well, I know I, m not a good mechanic, but I'm not understanding your last forum. The pump doesnt turn on until I hit the key and crank it witch would bring up the pressure. ( No initial prime) I'll back test the green wire as suggested, but the prob. Now is even when it does kick on there is no fuel coming out the injectors.
It is getting spark and the oil is good and I have fuel. Would what you said keep it from getting fuel? What does mod say about the voltage?
Between my k5 military blazer and this suburban I'll be a great mechanic yet. Neither seems to be to dependable lately
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Friday, January 15th, 2010 AT 6:19 PM
Tiny
JDL
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You should get the initial prime even without rpm signal. Engine cranking, if no rpm signal, the injector/s won't pulse, and there will be no voltage from computer to relay. I thought you were asking about initial prime?

I just wanted to add, if no battery voltage at the dark green wire with white tracer, problem with the wiring circuit--harness connector--ecm.
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Saturday, January 16th, 2010 AT 9:36 AM
Tiny
ALASKALOGGER34
  • MEMBER
  • 6 POSTS
Ok fellas, I tested the green/w wire at the computer and turned on the key -0.03 when I crank the engine no change. Also there is no movement at the rpm needle while cranking? Only if I give extended crank does the fuel pump kick on. But no fuel at injectors. Oh? I left the blue plug in at the puter this time and there is no voltage registering what next?
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Monday, January 18th, 2010 AT 12:53 PM
Tiny
JDL
  • MECHANIC
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Hi, check for trouble codes, see if anything shows up? Also, use a noid lite, if you haven't already on the injector plug, see if there is a pulse, engine cranking?

No voltage for the dark green wire with white tracer, at the computer pin. I suspect the computer.
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Monday, January 18th, 2010 AT 1:24 PM

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