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

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  1. #1
    Carb and Points!
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    1988 K5 Blazer 5.7l TBI will not run - need help!

    Been working on this for a long time. Here is list of new stuff:

    1. spark plugs and wires.
    2. Ignition control module.
    3. Fuel pump assembly. then just in case another new fuel pump
    4. 2 new fuel filters
    5. Fuel pump relay
    6. battery
    7. Starter

    So I did the following - FYI they all result in NO START:

    1. Tested voltage at relay. With key on I have 12v at power IN connection

    2. When turning the key I have 12v for about 2 sec at the output side of the relay.

    3. I tested the other end of the output from the relay at the fuel pump assembly and have 12v for 2 sec.

    To me the means that the existing wire is OK!

    4. When turning key and holding the relay in hand can feel the click and 2 sec later another click.

    5. Connected 12v to red wire (relay bypass) at relay. I have 12v at the fuel pump assembly.

    6. Connected new 14 gauge wire (temporary splice) from "relay out" to the fuel pump assembly. I have 12v at the fuel pump assembly.

    7. I have tested the ground from fuel pump assembly to frame using continuity. Result is .000 on the meter.


    Following resulted in fuel flow and start.

    a. Connected power directly from battery to fuel pump assembly.


    So if I am getting 12v to the fuel pump assembly via the existing wire and the temporary new wire why doesn't it run the fuel pump and start ?

    Been reading and wondering if the cause is a lack of a engine start signal or an engine running signal? I have been unable to find what creates these signals.

    Am I correct that while I have the initial 12v at the pump, that voltage stops after 2 sec and without the appropriate start or running signal voltage to the pump is cut off ?

  2. #2
    RIP EagleMark's Avatar
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    On the ECM pin B2, see if it gets power during the 2 second prime when key is on? If not fix it, look at diagram. If it does? Replace ECM...

    If you have a known good working 1227747 ECM just plug it in with your chip and try

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

  3. #3
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    The original circuit included an oil pressure switch that would also close if oil pressure existed at the engine. This switch may have been hiding another problem and may have recently failed. Use the wiring diagram and test for power and ground at various points to determine what's going wrong.
    Last edited by 1project2many; 06-26-2013 at 10:21 PM.

  4. #4
    Carb and Points!
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    Still not starting

    New ECM - no start - fuel pump not running.

    To reiterate new parts:


    Spark Plugs / Wires
    Oil Pressure Switch
    Fuel Pump Relay
    ECM
    Fuel Pump - Entire Assembly
    Battery

    I have power for 2 sec while cranking at the following places:

    ECM port B2, Fuel Pump in , Out side of fuel Pump Relay.

    Following copied from another post so people don't have to scroll back - all result in NO START:

    1. Tested voltage at relay. With key on I have 12v at power IN connection i.e. "A".

    2. When turning the key I have 12v for about 2 sec at the output side of the relay. "E"

    3. I tested the other end of "E" at the fuel pump assembly and have 12v for 2 sec.

    To me the means that the existing wire is OK!

    4. When turning key and holding the relay in hand can feel the click and 2 sec later another click.

    5. Connected 12v to red wire at relay. I have 12v at the fuel pump assembly.

    6. Connected new 14 gauge wire (temporary splice) from "E" to the fuel pump assembly. I have 12v at the fuel pump assembly.

    7. I have tested the ground from fuel pump assembly to frame using continuity. Result is .000 on the meter.


    I replaced the oil pressure switch a few days ago and today replaced the ECM. Still not starting, fuel pump does not run. I wish I could understand the wiring.

    Does anyone know if it works like I suspect, as follows:


    1. Cranking activates the fuel pump relay for 2 seconds to prime the fuel lines.

    2. Cranking causes oil pressure to build. When it reaches 4 lbs the oil pressure switch closes allowing the fuel pump to continue to run.


    Also, Since the engine runs when I apply 12v directly to the fuel pump does that CONFIRM that my Coil, Pickup coil, Spark plugs and wires, distributor cap, rotor, TCM are all ok ?

  5. #5
    Fuel Injected! jim_in_dorris's Avatar
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    I have to suspect something else is wrong. Try testing your fuel pressure at the throttle body. If the pump primes for 2 seconds like it should, you should have pressure at the throttle body. If it immediately bleeds back, then you wouldn't have fuel to get a start condition. With the pump running constantly, the bleed down problem would be masked. Won't guarantee that is the problem, but something to think about.
    Square body stepsides forever!!!

  6. #6
    RIP EagleMark's Avatar
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    On B2 there should be a 2 second on with key on, as soon as you turn to crank it should again have power. Yours does not? Mine does I just checked!

    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.

    Do you have power at Orange wire B1 and C16 Batt Power? Key off, key on, key Crank?

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

    I'm wondering if your ignition swicth at bottom of column is faulty?

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

  7. #7
    RIP EagleMark's Avatar
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    Don't bother, it's not the key switch, it may be the ignition switch on bottom of column that is activated by a rod from key cylinder...

    Your trying hard and this is not an easy find, I've never seen it before. But go through this before you go and just replace another part, I'm trying to figure out what is wrong?

    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. Mine does I just checked! Yours does not? Why?

    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.

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

    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'm wondering if your ignition switch at bottom of column is faulty? This will prove ECM has all Batt power and Ign power needed for operation. Something is not triggering fuel pump relay in Crank! But it does Key On?


    SO, is it ignition switch faulty and loosing power to ECM? Or id ECM not getting a crank signal during crank at C9?

    I brought up the C9 Crank signal in your other thread at CK5 but never heard back? It's a wire on starter solinoid to ECM C9... since it runs with power to fuel pump? And not if relying on ECM to trigger fuel pump relay, my bet is on no Crank signal from C9?

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

  8. #8
    Fuel Injected!
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    black ground wires on the engine block,or battery ground to body?

  9. #9
    Fuel Injected!
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    have you checked the ignition module? more than once i have found a bad ignition module to be the cause of a no start on a chevy tbi ( sometimes will even have spark but no injector pulse) a set of noid lights to test injector pulse might help too................just my thoughts................

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