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Thread: Fuel pump issue

  1. #1
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    Default Fuel pump issue

    So I bought an 86 vett that's a bit of a project. Im not getting power to the fuel pump...again. I will start from the beginning, I had an intermittent crank issue so I bypassed the starter enable relay by cutting the two wires and splicing them together and now it will crank just fine. I got it to run with good fuel pressure. I also had intermittent LCD screen issues so I went ahead and replaced every single fuse in the fuse panel and now the LCD screen works but the fuel pump won't turn on. I get power to the FP fuse for 2 seconds after turning the key as well as when I crank the engine. I replaced the entire fuel sending unit including a new fuel pump because it was shot and rusty. I have tried applying power to the G terminal of the ALDL with no luck as well. I am getting a signal for the fuel level, not sure what that means though..lol. I just use a light tester on the red wire at the fuel pump connector and ground it to a bolt on the fuel filter lid to test it and it seems like il
    getting no power to the fuel pump. Looking at a wiring diagram, it looks like the power wire from the fuse goes straight to the fuel pump, although it is different colored. Any ideas?

    FYI: I'm no mechanic, but pretty handy and get do most tests with the tools I have, so if I sound like an idiot, bare with me..lol

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    So messing with it today I hooked up a multimeter to the red incoming wire at the fuel pump and grounded the Meyer to the black wire and once I turn the key to ignition I get a constant 10v reading, it doesn't change whether I crank or not. Does that mean I have a bad fuel pump?

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    Quote Originally Posted by Nick0187 View Post
    So messing with it today I hooked up a multimeter to the red incoming wire at the fuel pump and grounded the Meyer to the black wire and once I turn the key to ignition I get a constant 10v reading, it doesn't change whether I crank or not. Does that mean I have a bad fuel pump?
    Should be a Tan/White wire coming from the FP fuse to the sender.
    Are you sure the wires to the pump terminals are secure?

    The fuel level sender uses the Pink wire and the Black wire which is ground.
    The schematic doesn't show where the fuel pump motor gets grounded.
    Remove the sender assembly and trace the wire from the negative terminal of the fuel pump motor and see if it has continuity to the Lug where the Black wire is.

    Also with the sender assembly out of the tank you can apply 12 volts direct to the fuel pump motor.
    If it runs don't run it for more than a couple of seconds.

    If the pump doesn't run, use your ohm meter and check the resistance of the fuel pump motor winding's.
    I'd imagine it's less than 100 ohms.

    Make sure the polarity of the wires at the pump are correct or the pump will run backwards.

    Last edited by ecss; 07-06-16 at 07:57 PM.

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    Awesome, thanks for the help. Ill pull the sending unit tomorrow and try to power it up off of my car battery to see if it'll fire up. Could just be a faulty pump, I just bought a brand new sending unit from rock auto with the pump attached already. I hope it's that easy, it's been quite a pain in the ass

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    First of all,....I don't know if it applies to 86's, but something you said intrigued me. You said, "When I turn on the ignition or crank it, I'll get voltage for 2 seconds." Does your Vette have the oil pressure lock out switch at the sender behind the base of the distributor????

    My '90 has 2 switches mounted there. One is the sender for the oil pressure gauge(small normal GM o/p sender) and is common on almost all small blocks. The other(larger switch, about the size of a 3/4" deep socket, I believe with 3 wires) senses oil pressure to "lock out" or kill the engine if NO oil pressure is present. Should it NOT sense O/P it will only close(allow current) to the fuel pump circuit for 2 seconds. You can test this initially by getting in the car(in a quiet environment) and turning the key to "on." You will hear the pump run for 2 seconds and then stop. You can turn the key off and try it as many times as needed. It will only run for 2 seconds until you get O/P. Check the switch, wires and connector at the O/P switch if your model has this.

    Also make sure all your grounds are good and clean. Most intermittent problems on these cars are caused by bad grounds. Do yourself a BIG favor and get a Factory Service Manual on CD from Corvette Central. They are about $25.00 and worth their weight in GOLD! Be sure to get the "RED COVER" version.

    Plus make sure you are connecting your test light to a true ground. The gas door mounting bolts are NOT grounded to the frame if I remember correctly. Ground the test light to either the battery negative or the frame by means of a long jumper to be sure. Remember these cars have a fiberglass body and that could send you on a "Wild Goose Chase!".
    Last edited by DonB; 07-06-16 at 11:54 PM.
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    Good work with mm; most can't do much more than point n click for repairs nowadays (or blindly 'plug n Pray, with a new part).

    MM is SECOND most important tool for EFI / TPI car. FIRSTmost is FSM factory shop manual, NOT Haynes / Chilton's.........

    edit:
    If you're testing the fuel pump OUT OF CAR, DO NOT APPLY POWER MORE MORE THAN A FEW SECONDS. Immersion in gasoline keeps the pump from burning up.

    Can you get a Fuel Pressure Gauge? Before removing do static pressure test. Fuel pressure is IMPORTANT...
    See my video here - same principle for L-98:
    <iframe width="420" height="315" src="https://www.youtube.com/embed/RAf6Itb0r2Q" frameborder="0" allowfullscreen></iframe>

    Quote Originally Posted by Nick0187 View Post
    So messing with it today I hooked up a multimeter to the red incoming wire at the fuel pump and grounded the Meyer to the black wire and once I turn the key to ignition I get a constant 10v reading, it doesn't change whether I crank or not. Does that mean I have a bad fuel pump?
    Last edited by Schrade; 07-12-16 at 09:16 AM.
    Never got a nickel for wrenchin', so I know nuthin'...

    Get rid of your electrons. Be positive (+).



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    b4 takeing out the sending unit , test the pump wires with a meter turn key on e you should have 12 volts i believe to the pig tail if no power the problem isnt the pump, also check the relay listen see if its clicking on when you hit the key

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    Quote Originally Posted by DonB View Post
    The other(larger switch, about the size of a 3/4" deep socket, I believe with 3 wires) senses oil pressure to "lock out" or kill the engine if NO oil pressure is present. Should it NOT sense O/P it will only close(allow current) to the fuel pump circuit for 2 seconds. You can test this initially by getting in the car(in a quiet environment) and turning the key to "on." You will hear the pump run for 2 seconds and then stop. You can turn the key off and try it as many times as needed. It will only run for 2 seconds until you get O/P. Check the switch, wires and connector at the O/P switch if your model has this.
    Yep! They're on the GM V6's 3.1's as well. Had two of them go bad on me in the past. And right, it looks about the size of a 3/4 inch socket. Turn the key, pump primes... Done! They use a special socket to replace them. If the oil pressure don't come up when the key is turned, the pump won't turn on. I believe if you're driving and the part fails, the engine will turn off. If yours is old, I'd replace it anyway, if only as a preventive maintenance action and to have a known good part in the mix.

    I'm wondering if the crankshaft sensor is bad if it will produce the same symptoms. I'm also wondering if there's a fusible link involved. I had a FL that would test ok, but when higher/normal current was applied it would fail. It even looked Ok. Someone told me about this, and I jumped/bypassed the link, and sure enough, the link was bad.


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