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Starting / running problems with 1988 K5

Discussion in '1973-1991 K5 | Suburban | Truck' started by THEMCGUIRE, Sep 6, 2013.

  1. THEMCGUIRE

    THEMCGUIRE 1/2 ton status

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    Had another thread called "88 K5 will not start...need help " and we got it running.

    Now however, after running for about 1/2 hour it just died. If I run power to the fuel pump relay bypass the fuel pump runs.

    When NOT using the bypass the fuel pump will not run, and the radio is dead, the horn does not work, tail lights and head lights don't work

    but the reverse, break, and turn signals do work..

    Battery is good. Checked all fuses and they are all fine. Checked all connections to the ECM and they are in place. This is a new ECM btw.

    The check engine lite, which is always on, is now off. And jumping ports 1 and 2 using a paper clip on the code test block does not function. Not even a code 12.

    Tested voltage at the 3 connections to the MAP and I have zero volts at all three electrical inputs.

    Stumped... any advise appreciated....
     
  2. MrSchaeferPants

    MrSchaeferPants 1/2 ton status Premium Member

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    You just do a visual on the fuses? I always touch them with a multimeter to verify continuity. That's a lot of things not to work.

    If the fuses are good, then I'd stick the prongs of the multimeter into the panel, check for voltage. If no voltage I'd check on the incomming power wire to the panel. If certain things on the panel have power, and certain things don't. I'd assume the fuse panel has some kind of issue.

    For the fuel pump, when you bypassed, you hooked an external source of wire to it? Directly from your battery or some other means?
     
  3. THEMCGUIRE

    THEMCGUIRE 1/2 ton status

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    Thanks for the response..

    I went from the battery to the red bypass on the relay. Fuel pump ran when I did that.

    ok will do a closer examination of the fuse box.
     
  4. crazedyak

    crazedyak That Guy Premium Member

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    1) Does the engine crank over, but not start?

    2) No SES when key is in the "ON" position right?

    If the SES light does not come on.... I know this is gonna sound crazy, but we need to check a few things on the No SES side before we jump too far into the fuel electrical system.

    I have the Manual with troubleshooting chart in front of me... The answer to the 2 questions above will help me narrow down the options

    Yak
     
    Last edited: Sep 7, 2013
  5. crazedyak

    crazedyak That Guy Premium Member

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    NO SES LIGHT

    ---DOES THE ENGINE START-- YES

    1) Ignition Off
    2) Disconnect ECM connectors
    3) Ignition On
    4) Probe circuit 419 (brown/white) wire with test light to ground
    5) Does the SES light come on?

    If Yes
    1) Faulty ECM connection or faulty ECM

    If No
    1) check fuse
    2) faulty SES bulb
    3) Open in circuit 419
    4) Circuit 419 shorted to voltage
    5) Open Ignition feed to bulb



    DOES THE ENGINE START -- NO

    --- Is the continuous battery fuse and ECM fuse OK?

    NO
    1) Locate and correct Short to Ground in circuit that had a blown fuse.

    --- Is the continuous battery fuse and ECM fuse OK?

    YES
    1) Ignition Off
    2) Disconnect ECM connectors
    3) Ignition On
    4) Probe Circuit 340 (orange) and circuit 439 (pink/black) with test light to ground
    5) Is the light "On" on both circuits?

    YES
    1) Faulty ECM grounds or faulty ECM

    NO
    1) Repair open in Circuit that did not light the test light.


    Do that check to clear your No SES light first... if the fuel pump issue still exists after that We'll tackle it. I had a similar issue, and found that a ground in the 419 circuit leading to the ECM which caused the ECM to just shut down everything fuel related. This may be your problem, but before we jump into the fuel system side we need to clear the SES issue first... they're likely the same issue.
     
  6. THEMCGUIRE

    THEMCGUIRE 1/2 ton status

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    Had to look up SES on the web. Duh. ok Service engine soon light.

    The engine will turn over. Have not tried to start when bypassing the fuel pump relay yet.

    I will check all this Monday and get back to you. Thanks for the detailed troubleshooting guide.

    ( The wife does not allow me to work on this on Sunday)
     
  7. crazedyak

    crazedyak That Guy Premium Member

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    No worries. Take you time. Don't try to get the engine running with the fuel pump bypassed. The fact that the engine turns over is enough to say yes/no to that troubleshooting chart.


    Just so you know I had a very similar issue recently. Engine would turn-over, but not start. Never heard the fuel pump prime, assumed bad fuel pump but decided to check voltage at fuel pump and discovered NO 12VDC at the fuel pump. Scratched my head as I checked the entire power wire from the pump to the ECM. Then I realized I did not have a SES light at all. So I started checking power voltage at the ECM connector voltages and signals. I found a ground issue in the ECM. When I fixed that all of a sudden my SES Light problem was fixed and my fuel pump issue was solved too.

    The ECM is the "brain" and if any signal going into the ECM is messed up then other problems will pop up that make you think something else is the culprit.
     
  8. THEMCGUIRE

    THEMCGUIRE 1/2 ton status

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    ok.

    Taking a look at the following wiring diagrams I do not see the circuits you refer to:

    http://coloradok5.com/forums/showthread.php?t=302678

    These are all A, B, C or D and then a number.

    What wiring diagram are you referring to to get your numbers ? 419 340 and 439 ?

    =============================================================

    Looking more I find that Connection A5 is brown/ white and labeled on master diagram as "Systems Check Light" Is this the one you mean ?
     
  9. crazedyak

    crazedyak That Guy Premium Member

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    [​IMG]

    In the middle of that schematic you see the Fuel Pump Relay Circuit... The SES Lamp, pink/black 430 on the left and brown/white 419 on the right of the lamp.

    The schematic and troubleshooting guide I am using is off the Original Chevrolet 1987 Light Truck Fuel, Driveability and Emissions Service Manual. This manual cover Fuel Injected Gas Engines to include the 1988 C/K Model.
     
  10. THEMCGUIRE

    THEMCGUIRE 1/2 ton status

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    results

    The wife went to her mom's. So I went out to try this.

    Results:

    Jumped test light from Brown/White (A5) to battery negative. Test light comes on and the SES lit dimly.

    Jumped A5 to to A12 (labeled ground). SES Lights brightly.

    Your instructions say:

    ---DOES THE ENGINE START-- YES

    1) Ignition Off
    2) Disconnect ECM connectors
    3) Ignition On
    4) Probe circuit 419 (brown/white) wire with test light to ground
    5) Does the SES light come on?

    If Yes
    1) Faulty ECM connection or faulty ECM

    What do you mean by Faulty ECM connection ?

    How do I know if it's a connection or the ECM ? This ECM is only a few weeks old fyi.

    Could I have fried the ECM when the fuel pump power line shorted out, I did not have line in snugly and it laid against the exaust pipe and melted and blew the ECM B fuse.

    AND the Horn, headlights, and radio don't work and I do not see any connection from them to the ECM...
     
  11. crazedyak

    crazedyak That Guy Premium Member

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    Now that you know the ecm or ecm connector is the issue... time to start checking individual connections on the ecm connector.

    I'd focus first on checking for a short to ground on each connection of the original circuits we talked about above in the ecm connector. Set a multimeter to Ohms and connect negative terminal of multimeter to ground (battery, assuming battery is connected to engine) and start going thru each applicable pin in the ecm connector. When you find a power cable that shorts to the battery... you have found the wire that has a short to ground in it. Start taking every inch of the wire until you find the issue.

    I'm not an electrical genius, and there may be a better method to do this.... it's worked for me in the past so I still use the method.
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    Sounds to me like you blew a fusible link. Headlights are not fused, therefore it's either a problem with the connector at the firewall, or connections between the battery + and headlight switch. Fusible links are what supply ALL power to the truck, and the headlights and ignition side are on separate links. This is how your headlights work independent of the ignition switch.

    Check for 12V at the junction block on the firewall (drivers side, inboard of the brake booster, should have two metal posts, black plastic protective posts that stick out) then check the other end of the two red wires that attach to the firewall connector. There should be a fusible link on each one of those wires, and one of them is most likely dead.

    I'm assuming you've checked the fuse "sockets" for voltage.

    Without looking at the wiring diagram, the SES power may come from the same power feed (fusible link) as the headlights.
     
  13. THEMCGUIRE

    THEMCGUIRE 1/2 ton status

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    Will check those links 1st, if not them I will continue with the ECM.

    Am I correct that the lights, radio, and horn do not have anything to do with the ECM ?
     
  14. dyeager535

    dyeager535 1 ton status Premium Member

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    Correct, other than possible power feeds being shared between them.
     
  15. THEMCGUIRE

    THEMCGUIRE 1/2 ton status

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    Thanks for the help.

    First off, thanks for the help!!!!

    Solution:

    Went to check the fusible links ... Heard a click, what was that? Long story short there was a red power line going into the firewall side of the fuse box. Moved it, heard click from the fuel pump relay. Repaired it and now horn, lights, radio and SES work.

    No fuel pump running. Open fuel tank filler and find the ground wire that I spliced a longer piece to was barely connected. Fixed that got 12 v.

    Still no fuel pump. Was checking everything and it wound up to be the connection from the pump to the bottom of the fuel pump assembly.

    Had some spare connectors from replacement fuel pump box. Replaced wires, started right up.

    Thanks again all...
     
  16. dyeager535

    dyeager535 1 ton status Premium Member

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    Excellent. Nice when it works out finding the problem just because you have happen to be working in that area. :)
     
  17. THEMCGUIRE

    THEMCGUIRE 1/2 ton status

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    Thanks Crazedyak and Dyeager for your help with this...

    Check out my WTF Do I do now - 1988 K5 thread in a week or so. Will be posting pics of the finished interior then. Just waiting for some interior paint and new inner doors.
     

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