Cranks, has spark but no start?

MATHIES.DEWULF

MEMBER
1989 GMC SIERRA
5.0L
V8
4WD
AUTOMATIC
175,000 MILES

Hey, I a few months ago I bought a gmc k1500 5.0L V8 TBI from 1989. When I first got it, it had no spark or fuel. I replaced the ignition coil, pickup coil and ignition module so now I have spark again. The following problem occurs. The fuel pump doesn't prime when I turn over the key or crank it for a while. The fuel pump works because if I apply 12V directly to the fuel pump it goes bzzz. I also have no 12V coming from me ECM to the green/white wire to the fuel pump relays. The orange wire is hot. And also, very weird thing with the fuel pump relays the green/white wire goes to F and the black/white wire goes to D+ on the relays isn't it supposed to be the other way around?

sorry for my bad English I'm from Belgium.
hope someone can help me I would be thankful for all eternity.

5 Replies

MATHIES.DEWULF

MEMBER
4 POSTS

And oh, it can also run on LPG. :)

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Wednesday, February 22nd, 2023 AT 7:20 AM

MATHIES.DEWULF

MEMBER
4 POSTS

And is it like normal that it has so many free slots?

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Wednesday, February 22nd, 2023 AT 9:09 AM

JACOBANDNICKOLAS

MECHANIC
108,297 POSTS

Hi,

The black/ white wire should be a ground path from the primary side of the relay. When the key is on and the engine running, power from the green/white wire (fuel pump driver at PCM) powers the primary. That is what actuates the relay. If you are not getting power at the green/white wire, the PCM may be faulty. Keep in mind, the oil pressure switch is tied into this as well. If there is an open or no pressure, it will shut down fuel.

See the schematic below. Also, take a look at this link. You may find it of interest.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Let me know.

Joe

See pic below. Also, I believe there should be more fuses than I see. Is that under the hood?

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Wednesday, February 22nd, 2023 AT 8:05 PM

MATHIES.DEWULF

MEMBER
4 POSTS

Thank you very much for answering.

I checked the oil pressure switch by blowing in with high pressure and measuring for resistance. It showed verry low resistance and the multimeter beeped. I was very gentle with the high-pressure gun mounted on the compressor. When I jumped the red/black and orange wire (which was hot) the fuel pump buzzed for as long as I jumped it but with a different tone, than when I jumped the fuel pump directly.

Is there any way I can test if the PCM is faulty?

And it is under the dash behind the fuse box.

Thanks for the link you sent me. I'll get a testing light tomorrow and do some more testing.

Thanks already for the help.
I saw the website is funded with a GoFundMe is there a link where I can donate? :)

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Thursday, February 23rd, 2023 AT 1:30 PM

JACOBANDNICKOLAS

MECHANIC
108,297 POSTS

Hi,

Where are you getting the red/black wire? I see the orange in the schematic, but not the red/black.

As far as testing the PCM, you could check for power out 12v driver out from the PCM for power. (Green/white wire).

Do me a favor. If you haven't already, check to see if there are diagnostic trouble codes. This had an obd1 system that doesn't require a scan tool to retrieve codes. Follow the directions in this link. All you will need is a short jumper wire or even a paper clip.

https://www.2carpros.com/articles/buick-cadillac-chevy-gmc-oldsmobile-pontiac-gm-1983-1995-obd1-code-definitions-and-retrieval-method

Also, the GoFundMe link is https://gofund.me/c7d318ad

Anything you offer is appreciated.

Let me know what you find with the truck.

Take care,

Joe