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Thread: 1988 K5 Blazer 5.7l TBI will not run - need help!

  1. #16
    Carb and Points!
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    New Update

    I think I covered all the posts above with these tests:

    Can you hear the pump run with key on, engine off? NO

    Can you hear the pump run when the relay is jumped? NO

    Can you hear the pump run when power is applied from battery to pump? Yes a few days ago, now NO ???????


    So I bought a test light

    On B2 there should be a 2 second on with key on even if you don't go to crank, as soon as you turn to crank it should again have power.

    test light lights at B2 when turning on key that lasts for 2 seconds. On cranking I have power again.

    Then if there is a crank signal to C9 when key is cranked the fuel pump trigger at A1 turns relay back on and looks for the signal again at B2.

    test light lights when cranking to C9

    Do you have power at Orange wire B1 and C16 Batt Power? Key off, key on, key Crank? Should be hot always.

    test light lights at B1 and C16 under all 3 conditions.

    Do you have power at Pink wire A6 Ignition, should be hot key on and key crank? Should be hot key on and key crank.

    test light lights at A6 both conditions.

    Also went back and tested C3. The test light lights with key on but does not light during cranking,

    Note: With the engine connected via jumpers to a running car, the starting rotation rate during cranking is now very sluggish, but I sprayed a small shot of starter fluid and it started right up and ran until the started fluid was gone.


    A reminder so scroll back not needed, I have replaced so far:

    Spark Plugs and wires, ignition switch, Fuel Pump Assembly, Fuel Pump, Fuel Pump relay, Fuel Filter, Oil Pressure Switch, Battery, and the ECM.

    Reminder: The engine ran when I put direct connection from battery directly to the fuel pump a few days ago.


    Using Bypass wire on relay I have power at purple wire at fuel pump assembly.

    Attached the test light to positive power and tested the ground wire at the fuel pump relay and at the bolt where the ground meets the frame. Test light lights up. So ground is good.

    Again put 12 volt from battery to fuel pump. This is a brand new fuel pump. No WHIRRING this time. Could I have burned out the fuel pump with all this testing ?

    Can the fuel pump be tested OFF the truck ? Put in a bucket of water and apply 12v ? will water hurt the pump ?

    I am lost!
    Last edited by themcguire; 07-06-2013 at 06:50 PM.

  2. #17
    Fuel Injected!
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    you might try banging on the bottom of the gas tank, where the fuel pump-gauge wires connect to the top of the fuel pump holder my need unplugged an cleaned, in side the tank.

  3. #18
    RIP EagleMark's Avatar
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    Quote Originally Posted by THEMCGUIRE View Post
    Bought a $5.00 test light

    On B2 there should be a 2 second on with key on even if you don't go to crank, as soon as you turn to crank it should again have power.

    I have power at B2 when turning on key that lasts for 2 seconds. On cranking I have power again.Check!

    Then if there is a crank signal to C9 when key is cranked the fuel pump trigger at A1 turns relay back on and looks for the signal again at B2.

    I have a light when cranking to C9Check!

    Do you have power at Orange wire B1 and C16 Batt Power? Key off, key on, key Crank? Should be hot always.


    Yes I have power to B1 and C16 under all 3 conditions.Check!

    Do you have power at Pink wire A6 Ignition, should be hot key on and key crank? Should be hot key on and key crank.

    I have power at A6 both conditions.

    I have replaced the ignition switch.
    Check!
    Using Bypass wire on relay I have power at purple wire at fuel pump assembly. I then attached the test light to positive power and tested the ground wire at the fuel pump relay and at the bolt where the ground meets the frame. Test light lights up.

    Again put 12 volt from battery to fuel pump. THis is a brand new fuel pump. No WIRRING. No Good! Bad Fuel Pump if you had power and ground hooked up? Could I have burned out the fuel pump with all this testing ? Doubt it, I ran one on the wall off my test bench for years till I put in a light bulb...

    Can the fuel pump be tested OFF the truck ? Put in a bucket of water and apply 12v ? will water hurt the pump ? Why? It does not run?

    Also went back and tested C3. It lights with key on but does not light during cranking. C3 is a typo from wiring disagram copy, it's an IAC wire, disregard.

    btw - engine is connected via jumpers to a running car but rotation rate is now sluggish. So i sprayed 1 shot of starter fluid in and it started and ran until the started fluid was gone. Clean Batt terminals, charge batt, load test, should not need a jump start and still ne low power/slow crank. If something is drawing all this power there will not be enough left to turn on fuel pump relay!
    Reply in RED!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  4. #19
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    Reminder: You're testing current conditions. You're not testing yesterday, last week, or a month ago.

    Reminder: CSI and Sherlock Holmes both understand the importance of following the evidence to a conclusion, no matter how improbable it seems.

    Reminder: New parts can be faulty, too.

    I'd test pump in diesel or kerosene if available. Marvel mystery oil might work, too. Water would work for testing but if it's not the pump then you've got a bunch of water that you have to purge. As mentioned, problems can occur at connector under sending unit. Poblems can also be caused by faulty crimps, wires installed in wrong terminals, wires not actually connected to terminals, etc. Pull sender and check for continuity between pump connector and correct terminals on top harness. All indications seem to say problem is in tank sender or pump.

    Battery dead from continuous cranking without charging? Mark's right: Charge battery. If you've had it on a charger very recently it should be charged. If not, why??? More diagnosis would be needed. <sigh> Is this going to turn into one of those problems I only read about on the internet??

  5. #20
    Carb and Points!
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    OMFG... All along I was using the purple wire to the fuel pump assembly. It was the gray.

    We took the pump out. Immersed it into marvel mystery oil, applied 12v and it ran fine.

    Tested all the wires from both sides of the fuel assembly and found that the purple is for the gauge and the grey was for the pump.

    Ran a wire from the exit on the relay to the grey wire going to the pump and bang zoom she started right up.

    Please feel free to diss me for my stupidity in buying all those parts that I did not actually need.

    Oh well, you live and you learn.

    Thanks for all your help, advise and other comments.

  6. #21
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    I won't diss you for buying parts unnecessarily. This time. But never, never use parts replacement as a diagnosis tool unless there's no other way. :)

    We've all made mistakes. As a pro tech I have plenty of stories that I could share to illustrate. At least you've got it. Kudos for sticking with it to the end.

  7. #22
    Fuel Injected!
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    glad you got it fixed,every time you have trouble on a project this will proble flash through your mind

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