87 GN Fuel Pump Issues

Discussion in 'Sparky's corner' started by 2manybuicks, Mar 1, 2023.

  1. 2manybuicks

    2manybuicks Founders Club Member

    GN died saturday right as I started to head to Waterboy's get-together.

    Fuel pump works with computer by-passed, but is not getting power when hooked up normally.

    Options? Can I get another computer? Rebuild it? Just run it by-passed?
     
  2. FJM568

    FJM568 Well-Known Member

    Are you running Casper's Electronics fuel pump hot-wire kit or stock? Either way, check your relays. The stock one is on the passenger fender. If you're running the hot-wire kit, the factory relay is set up to trigger the hot-wire kit's relay, so you'll need to check both of them then.

    With the hot-wire kit, there is also a fuse, either mounted near the firewall, or near the relays on the fender, depending on where the installer mounted it.

    I'll try to upload the installation instructions for the hot-wire kit from Casper's.

    I don't recall if Racetronix had a kit, and if it differed much from how Casper's kit was made, but if you've got a Racetronix kit, it should be similar.

    Hopefully this will give you something to start looking into.

    Only other thing, is check your grounds. These cars are real finicky about them.

    Good luck.

    edit...quick check on the relays, if I remember right, the cooling fan and the fuel pump both used the same relay. Try swapping them and see if the fuel pump will work. There is also a one-wire pigtail somewhere, that when you put 12v to it, it will trigger the fuel pump to run. We used to drain the fuel tank through the fuel rail of pump gas, and put race fuel in for the track. Let me see if I can track down where that pigtail is at.

    edit #2...that connector should be a gray connector near the alternator. A 12v jumper wire should trigger the fuel pump to run.
     

    Attached Files:

    Last edited: Mar 1, 2023
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  3. Redmanf1

    Redmanf1 Gold Level Contributor

    Jim, that is some good info...^^
     
  4. 2manybuicks

    2manybuicks Founders Club Member

    This is the root cause, it seems. Even cleaned up, no power to fuel pump when connected.

    IMG_4028.jpg
     
  5. FJM568

    FJM568 Well-Known Member

    Is that your ECM harness?

    I don't know, but you might be able to de-pin and clean each terminal end....BUT, I believe Casper's sells a ECM harness splice end kit that would be easier. Wire colors are all matched to originals. Pretty easy fix.

    http://www.casperselectronics.com/c...uct/product&path=7_53_54_10_13&product_id=283

    It's a lot of splicing, but cheaper than a whole new harness. If you do go this route, stagger your splices so that they don't all end up in the same location in a big ball.

    But in addition to fixing that problem, you need to fix the source of the water leak that caused it. Might be windshield leaking, or T-tops if that's what your car is.

    Also, pull the main housing apart on your ECM. It's just a couple of screws. Check inside for water damage on the circuit board, but mainly the connectors for the harness to the board. Hopefully there's not any corrosion there.

    If you do get a replacement ECM, make sure, in addition to pulling your main chip out, that you also grab the smaller chip as well. That small chip will run the car in limp mode if the main board/chip fails, but it's only programmed with stock inj parameters.

    The ECM's used to be fairly common in the salvage yards back in the day. Most of the fwd 86/7 GM cars with a 3.8L motor had them and you could get them for fairly cheap to have as a spare.

    If you're needing one, check over on the TurboBuick forum for an original before you try to get a remanufactured one from the parts stores.

    edit...You didn't mention if your car has a fuel pump hot-wire kit. If you don't, I would recommend one. The stock fuel pump was barely adequate when these cars were new, and the voltage drop before the pump was enough that the pump wasn't even getting close to 12v. The hot wire kit solves that by supplying a full 12v through larger wiring directly to the pump.

    And Casper's is real good to deal with. They used to go to the Nats for years with their GN powered Cobra kit car.
     
    Last edited: Mar 2, 2023
  6. Redmanf1

    Redmanf1 Gold Level Contributor

  7. FJM568

    FJM568 Well-Known Member

    So...what's the verdict?
     
  8. 2manybuicks

    2manybuicks Founders Club Member

    Buying a new ECM from Highway Stars and a connector pigtail from Caspers.
     
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  9. 2manybuicks

    2manybuicks Founders Club Member

    Highway Stars just called me to clarify shipping. I mean, an actual human called. Lawsy, them is good people with great customer service. Wish they stocked more.
     
  10. 1973gs

    1973gs Well-Known Member

    Solder and heat shrink your splices. Butt connectors will be an issue down the road, even the heat shrink type.
     
  11. breakinbuick11

    breakinbuick11 Platinum Level Contributor

    Steve, do you have a chip in that? Might be a good time to order one from Eric at TurboTweak.
     
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  12. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    I would buy the tool and connectors and crimp. That many splices/repairs is begging for trouble!
     
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