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91 s10 4.3 no power to fuel pump

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6 years 3 weeks ago #18545 by gregster
Hi with key on the ecm green white wire has 11.70 volts w/o relay. With relay same wire is only reading 0.07 volts. Black and white wire is good ground.fuel pump works when org and grey wire is jumped. Any ideas?

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6 years 3 weeks ago - 6 years 3 weeks ago #18551 by Chad


It sounds like you have a voltage drop on the DK GRN-WHT wire. With the relay removed, you have 11.7 volts on the DK GRN-WHT wire. Will it light an incandescent test light?

This video explains voltage drops using a starter as an example.


"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)
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Last edit: 6 years 3 weeks ago by Chad.

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6 years 3 weeks ago #18552 by gregster

pole71 wrote:



It sounds like you have a voltage drop on the DK GRN-WHT wire. With the relay removed, you have 11.7 volts on the DK GRN-WHT wire. Will it light an incandescent test light?

This video explains voltage drops using a starter as an example.

Hi, my light didn't light, multimeter still showing 11.7 volts. didn't see a video attached to your reply. Thanks

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6 years 3 weeks ago - 6 years 3 weeks ago #18553 by Chad
A youtube search of " Multimeter basics, voltage and resistance tests (a free SD Premium video) " should find the video I was referring to. A search of "voltage drop testing" will net you many more.

A bad wire can show a voltage when there is nothing USING that voltage, but drop significantly when a load is added to the circuit. If you try to light the test light AND read the voltage at the same time, you will see the voltage drop. Connect your meter and watch the 11.7 volts. Now, add the test light while watching the voltage. Did the voltage drop? Now, move the the other end of the DK-GRN wire (at the ECM) with the volt meter. Try to light the test light at the relay socket. Did the voltage drop at the ECM?

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)
Last edit: 6 years 3 weeks ago by Chad.

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6 years 3 weeks ago #18556 by gregster

pole71 wrote: A youtube search of " Multimeter basics, voltage and resistance tests (a free SD Premium video) " should find the video I was referring to. A search of "voltage drop testing" will net you many more.

A bad wire can show a voltage when there is nothing USING that voltage, but drop significantly when a load is added to the circuit. If you try to light the test light AND read the voltage at the same time, you will see the voltage drop. Connect your meter and watch the 11.7 volts. Now, add the test light while watching the voltage. Did the voltage drop? Now, move the the other end of the DK-GRN wire (at the ECM) with the volt meter. Try to light the test light at the relay socket. Did the voltage drop at the ECM?

I put test light on at socket and volts did drop, put meter at ecm g/w wire and volts also dropped.

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6 years 3 weeks ago #18560 by Chad
If you are showing a voltage drop at the ECM, then we need to check the power feeds INTO the ECM for a drop. Pins A6, B1, and C16.


"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)
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6 years 3 weeks ago - 6 years 3 weeks ago #18564 by Tyler
pole71, I'm really not trying to be a jerk here. :blush: But, don't the GM fuel pump relay control circuits work this way by design? There's a bias voltage present on the dark green/white wire, as a circuit check on the control side of the relay.

This video is what I'm referring to:



Or, is this old news? 'Cause I'm sorry if it is! :silly:

Will the dark green/white wire light a test light during cranking? Or, during the key on fuel pump prime.
Last edit: 6 years 3 weeks ago by Tyler.
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6 years 3 weeks ago #18565 by Chad
Thank you, Tyler. There's no being a jerk about it.:cheer: Good call. I was un-aware of a bias voltage, being here. I was assuming the 11.7 volts was while trying to crank.

Thanks for the video and helping to fill in the gaps in my knowledge. I know there are many. But, I learn more every single day.

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)

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6 years 3 weeks ago #18580 by gregster

pole71 wrote: Thank you, Tyler. There's no being a jerk about it.:cheer: Good call. I was un-aware of a bias voltage, being here. I was assuming the 11.7 volts was while trying to crank.

Thanks for the video and helping to fill in the gaps in my knowledge. I know there are many. But, I learn more every single day.

Hi, so should I check power going in to ecm still, or is this normal? Should i check grn/white wire with light while cranking? Thanks

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6 years 3 weeks ago #18585 by Chad
Check the grn/white wire while cranking. You should see battery voltage and it should light the test light.

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)

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6 years 3 weeks ago #18598 by David56

pole71 wrote: Check the grn/white wire while cranking. You should see battery voltage and it should light the test light.

Ok . Passed I went out today to fine my problem. Placing my hand on the fusebox in the back. It was hot. So I opened it and I think I found the source. Turns out my number 58 relay was very hot. Unplug the relay but when I put it back it started snapping. Then I could here things coming on. Seconds later I heard a pop and everything shut down. That's were I am. Thanks. Dave

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6 years 3 weeks ago #18607 by Chad
Can you tell us what, or where specifically, Relay 58 is?

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)
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6 years 3 weeks ago #18609 by David56

pole71 wrote: Can you tell us what, or where specifically, Relay 58 is?

Lighter. Really. This isn't my first. I am 63 but I worked on these northstars when no one would. Been a while. The poping noise stopped everything. Nothing works not even dash
Noise sounded like it came from trunk. Thanks

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6 years 3 weeks ago #18610 by David56

David56 wrote:

pole71 wrote: Can you tell us what, or where specifically, Relay 58 is?

Lighter. Really. This isn't my first. I am 63 but I worked on these northstars when no one would. Been a while. The poping noise stopped everything. Nothing works not even dash
Noise sounded like it came from trunk. Thanks

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58 relay is in under back seat. In fusebox a twin to under hood. Thanks

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6 years 3 weeks ago - 6 years 3 weeks ago #18614 by Chad

David56 wrote: Ok . Passed I went out today to fine my problem. Placing my hand on the fusebox in the back. It was hot. So I opened it and I think I found the source. Turns out my number 58 relay was very hot. Unplug the relay but when I put it back it started snapping. Then I could here things coming on. Seconds later I heard a pop and everything shut down. That's were I am. Thanks. Dave

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My apologies, David56. But you have confused me, a little bit. :unsure: This thread was started by gregster for a 1991 s10. No power to the fuel pump. I thought I was replying to gregster and his S10.

If you need help on a different vehicle/problem, I encourage you to start a new thread stating your Year, Make, Model, Engine size, and a description of the problem you are having. :) This will help in minimizing any confusion.

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)
Last edit: 6 years 3 weeks ago by Chad.

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6 years 3 weeks ago - 6 years 3 weeks ago #18616 by Chad
David56, I found your thread.

www.scannerdanner.com/forum/post-your-re...-no-crank.html#18522

I will respond on it, soon.

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)
Last edit: 6 years 3 weeks ago by Chad.

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6 years 3 weeks ago #18656 by gregster

David56 wrote:

pole71 wrote: Check the grn/white wire while cranking. You should see battery voltage and it should light the test light.

Ok . Passed I went out today to fine my problem. Placing my hand on the fusebox in the back. It was hot. So I opened it and I think I found the source. Turns out my number 58 relay was very hot. Unplug the relay but when I put it back it started snapping. Then I could here things coming on. Seconds later I heard a pop and everything shut down. That's were I am. Thanks. Dave

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Ok there is no light at grn/wht wire when cranking. There is power at b1 a6 c16. Hopefully you get this old how other person is on my thread. Thanks Greg

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6 years 3 weeks ago #18663 by Chad
When you first turn the key to the "On" position (without cranking), the ECM should power the g/w wire for 2 seconds, then turn off. Does it?

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)

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6 years 3 weeks ago #18675 by gregster

pole71 wrote: When you first turn the key to the "On" position (without cranking), the ECM should power the g/w wire for 2 seconds, then turn off. Does it?

grn/wht wire doesn't light up at all when key is turned on.

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6 years 3 weeks ago #18681 by Chad
Since you have power on A6, ,B1, and C16, but get no power on the A1(g/w wire) when the Key is first turned on, or while cranking, I believe this is pointing to a bad ECM.

As a final check, I would verify good grounds on A12 and D1.

Does anyone have a second opinion?

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)

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