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'88 TBI no start

Discussion in 'The Garage' started by EXJAY, Oct 8, 2013.

  1. EXJAY

    EXJAY 1/2 ton status

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    Just got my father-in-laws '88 K5 (5.7 350) and was told it had fuel pump/no starting problems which is why he let it sit for a year. He originally told me the fuel pump would not prime when in "key on" position but when I got it towed to my place and started to look into it I can hear the pump prime now (maybe the tow and fuel sloshing around did something). SO... I've been researching/reading up on this issue and could be several things going on/causing no fuel to spray in the TBI. Just look to see wheres the best place to start in troubleshooting and looking for some input/suggestions. Here's what I came up with as the best logical order to start:

    Check pump relay for proper operating/voltage in "on" and "crank" positions (I know its getting power (good fuse) since i hear it prime) but is it possible that one side of the relay will power the pump to prime but when it switches over for the ECM to take over in the cranking/run position that side of the relay could be bad?

    Noid light to check pulse at injectors while cranking (if OK the ECM is good?)

    Check for proper fuel line pressure at prime and crank (if OK this should also confirm that the relay and pump are good?)

    if pressure is still "0" while performing fuel line pressure test I can assume the pump is bad? Fuel filter was recently swapped out and new battery installed btw.
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Forget the relay. It works if it primes, not the issue.

    Noid light is where I'd start. Checking pressure on these is tough, but may be necessary later. However, if no injector pulse, fuel pressure isn't going to matter anyway.

    It sounds like you want to verify the ECM is ok, which is a bad way to bias your thinking. The ECM is normally the LAST thing to suspect. Statistically, it is far more likely to be anything else, which is a fair number of things in a crank no start situation.
     
  3. mr.smartass

    mr.smartass 1 ton status Premium Member

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    I had the same issue on my 89, could hear the pump running in the tank but no fuel when I disconnected the line at the filter, dropped the tank and the little 1 or 2 inch piece of rubber tube connecting the pump to the sender had crumbled and fallen apart, pump was just spitting fuel around in the tank. Might have been from sitting in ethanol gas or just from being 24 years old. Something to think about.:dunno:
     
  4. EXJAY

    EXJAY 1/2 ton status

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    Thanks. Was hoping to rule out everything before having to remove the tank for a pump inspection/swap (its 3/4 full). Did pick up a noid light test set from AutoZone (loaner tool program) and will report the results this evening.
     
  5. rampage

    rampage 1/2 ton status Premium Member

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    Easy enough to check this. Disconnect fuel filter and connect a hose to a container to catch any fuel. Disconnect the wire harness at the fuel tank and connect 12V to the gray wire that goes to the tank and the pump should start spewing out gas (of course you need to connect ground to something suitable like the frame).
    If gas does come out then I'd empty the tank and put in fresh gas. Gas that old won't help matters when trying to figure out why it's not starting.
     
  6. eagle mark

    eagle mark 1/2 ton status

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    Actually easier then that. Hook 12 volt to red wire hanging from fuel pump relay. It has a clip on the end and is called a prime wire.

    Does the vehicle have spark? No spark = no DRP Distributor Reference Pulse and fuel pump will not turn on after prime.
     
  7. EXJAY

    EXJAY 1/2 ton status

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    Only had a short time this evening to mess with the K5. Verified with the noid tester I do have pulse at both injectors when cranking. Also for the hell of it I bench tested the pump relay and it is also good. I will have to check spark tomorrow to be 100% sure and report my findings but was told durring my Father-in-laws attempt to troubleshoot back after it first stopped running that there was spark. I rather just start from scratch in troubleshooting and not assume anything. Thanks guys!
     
  8. 4xcrazy

    4xcrazy 3/4 ton status

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    Shoot a couple of quick shots of ether down the intake, if it has any spark, it will ignite and try to start.
     
  9. eagle mark

    eagle mark 1/2 ton status

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    He verified he has spark with noid light firing injectors.

    If he has good spark! I even tried the either trick last week and no go...

    I just went through this on my sons 1988 Chevy TBI truck. Would not start cold. Had spark but I noticed the color was yellow? So me being an old guy knew that meant the points needed adjusting or replaced! :haha:

    D'oh! No points? So I got the GM diagnostic tests for the coil and sure enough it failed two of the three tests. Replaced coil and it runs like a top!

    Also checked spark once again with new coil and it was Blue. Much stronger and even had the audible SNAP when firing!

    We had issues with this truck earlier in year and found the button in distributor cap was just hanging there, no spring load, lots of black traces from misfires all over rotor. So replaced cap and rotor and it ran... but still had an issue... in checking the EST module in distributor it had a melted plug! Probably from the bad cap rotor button. So we pulled distributor to replace the pickup coil which was also fried! This got most issues fixed but still not quite right? Till the coil replacement.

    Seems the rotor button failure throwing 40k spark all over just fried everything! Truck has been daily driving no issues for a week... fuel mileage is way up. Amazing how these things will run even with faulty parts...
     
  10. EXJAY

    EXJAY 1/2 ton status

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    So if the ECM is sending pulse signals to the injectors it must be seeing fuel pressure at the TBI correct? Just trying to verify that the pump is working/doing what it should before moving on to troubleshooting an ignition issue. Thanks
     
  11. 4xcrazy

    4xcrazy 3/4 ton status

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    The computer doesn't know anything about the fuel pump. It is supposed to send the injector pulse from sensors and workings from the control module in the distributor. I have been fighting a random no pulse issue with mine for awhile now. new fuel pump, filter and various other items.
     
  12. euzoa

    euzoa 1/2 ton status

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    Maybe this will help you guys

    Chart A-3 - Engine Cranks But Will Not Run[​IMG]
    Wiring Diagram For Chart A-3 - Engine Cranks But Will Not Run[​IMG]

    CHART A-3 - ENGINE CRANKS BUT WILL NOT RUN

    Circuit Description :
    This chart assumes that battery condition and engine cranking speed are OK, and there is adequate fuel in the tank. This chart should be used on engines using the Model 220 throttle body.


    Test Description : Numbers below refer to circled numbers on the diagnostic chart.
    1. A "Service Engine Soon" light "ON" is a basic test to determine if there is a 12 volt supply and ignition 12 volts to ECM. No ALDL may be due to an ECM problem and CHART A-2 will diagnose the ECM. If TPS is over 2.5 volts the engine may be in the clear flood mode which will cause starting problems. If coolant sensor is below -30~C, the ECM will provide fuel for this extremely cold temperature which will severely flood the engine.
    2. Voltage at the spark plug is checked using Spark Tester tool ST 125 (J26792) or equivalent. No spark indicates a basic ignition problem.
    3. While cranking engine there should be no fuel spray with injectors disconnected. Replace an injector if it sprays fuel or drips like a leaking water faucet.
    4. Use an injector test light like BT8320, or equivalent, to test each injector circuit. A blinking light indicates the ECM is controlling the injectors.
    5. This test will determine if there is fuel pressure at the injectors and that the injectors are operating.
    Diagnostic Aids :
    If no trouble is found in the fuel pump circuit or ignition system and the cause of a "Engine Cranks But Will Not Run" has not been found, check for:


    • Fouled spark plugs
    • EGR valve stuck open
    • Low fuel pressure. See CHART A-6.
    • Water or foreign material in the fuel system.
    • A grounded CKT 423 (EST) may cause a "No Start" or a "Start then Stall" condition.
    • Basic engine problem.
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    I don't think disconnecting the fuel filter and checking flow will work. People have been able to start/run (but not normally drive) the vehicle if the hose has split, which means fuel IS flowing. I don't know how to determine fuel pressure based on my eyeball, unless the eyeball is looking at a gauge.

    As Mark said, checking spark isn't a bad idea. It is most likely ok (due to injector pulse), however it could be weak. It's easy enough.

    The way the system works, in an ideal nutshell, is this: Key to run, ECM switches fuel pump relay on for prime, then shuts it off until engine starts turning. Distributor turns as engine cranks, and via the signal from the distributor the ECM again switches the relay to provide fuel pump power, and at the same time begins pulsing the injector grounds (the injectors get 12V with key on). Just for a little background on what goes on to start.
     
  14. EXJAY

    EXJAY 1/2 ton status

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    Getting there....dont let me give up!

    ^Good stuff, thanks. Couple things I checked today was that if I put a little gas in the tbi and crank it over it will run for a few seconds then die so spark is there. Still saw no spray at the injectors so I seperated the fuel line where it enters the filter and drained what gas was standing in the line/filter. Turned key to "on" and could hear prime but no fuel came out on this line from the tank. Did this a few times w/ same results. Had someone crank it over a few times and no fuel still out of the line while it was turning over. Shouldnt it push fuel through while prime and cranking? Not sure yet if its the ECM not telling the pump to run correctly while cranking or the pump itself is bad (since i can hear it prime but maybe something seperated off the pump in the tank or just lost its pumping ability to pump but still trying to run?)
     
  15. euzoa

    euzoa 1/2 ton status

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    It could be a clogged inlet screen, or the line that runs from the pump to the sending unit
     
  16. eagle mark

    eagle mark 1/2 ton status

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    Should be loads of fuel coming out the fuel line when disconnected from filter! If you can hear pump running? Time to pull tank...
     
  17. euzoa

    euzoa 1/2 ton status

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    Now someone correct me if I'm wrong, One of my instructors told me that the used to run air pressure back into the tank to blow off the screen if it got clogged (with the gas cap off, you will shorten the life of the pump obviously, but it would let you empty the tank before you drop it.

    I don't know if it will hurt anything else though, if someone else wants to chime in I'm curious myself
     
  18. eagle mark

    eagle mark 1/2 ton status

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    That worked well on carb engines. Not sure how it would work blowing through an in-tank pump?

    May be a good diagnoses but if the screen is plugged with crap and you blow it off? It will eventually collect there again and clog.
     
  19. euzoa

    euzoa 1/2 ton status

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    I bow to your judgment sir, I just tried to breath through the new sending unit and pump I have sitting in my closet...no go, and 120 psi of shop air would probably blow that rubber line apart if the pump didn't give
     
  20. EXJAY

    EXJAY 1/2 ton status

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