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At a loss, need some help with 88 TBI..Shuts down.

Discussion in 'The Garage' started by chevyracing, Apr 8, 2003.

  1. chevyracing

    chevyracing 1/2 ton status

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    Location:
    Colorado
    1988 Chevy 1/2 ton pickup
    350 TBI
    Auto tranny
    Marshall crate engine

    Here is the problem;

    The truck shuts down intermitingly. If you start it and let it run for about 3 or 4 minutes it shuts down and will not restart for a while. My Brother in Law drove it out from Iowa and it ran just fine. We took the ecm to NAPA and the checked it several times and it checked okay each time, we changed the fuel filter, fuel pump and the fuel pump sensor. Still does it.

    Here is my next guess. I think there is an oil pressure problem. The guage reads low so I believe when the engine starts to warm up the oil thins out enough and the pressure drops even more so the sensor shuts the engine down. I am going to hook a mechanical guage to the engine to see if in fact it has low pressure or a faulty sending unit. If the sending unit is good then the oil pump is bad or there is too much main bearing clearance, right? Another possibility is when they rebuilt the engine the plug by the oil pump was not installed or installed incorrectly, right?.......... /forums/images/graemlins/confused.gif

    My question is this;

    1) The sensor for the oil pressure can be temporarily bypassed, ,,,how? (I need to be able to do this so I can hook the mecahnical gauge to it since it does not have the plug by the cam cover.)

    2) What ever possesed him to buy a P.O.S. Marshall engine?

    Thankyou for all of your help in advance..

    John
     
  2. HarryH3

    HarryH3 1 ton status Author

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    The oil pressure switch is there to bypass a defective fuel pump relay... It will send power to the fuel pump in the event the relay doesn't. It would only act as a low-pressure shutoff switch if the relay isn't working.

    Does it have spark when the engine won't start?
     
  3. chevyracing

    chevyracing 1/2 ton status

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    Yes it does, if we pour fuel down the throttle body it starts and runs until the fuel is spent. The spark is there but something is shutting the fuel supply at the throttle body off. There is fuel pressure to the throttle body. When it would not start we took the fuel line off of the back of the TB and it was pumping good. There is something somewhere I believe sening a signal for the TB not to squirt the fuel, but whhere and why is unbeknownst to me.

    John

    John
     
  4. 89K1500Chevy

    89K1500Chevy 1/2 ton status

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    Ummmm it sounded like spark to me but since it runs while pouring gas in it..... anyways try new Injectors that 88 model shouldnt have a shut off switch on it if it does thats odd cuz my 89 doesnt i had the oil pressure sending unit out and blocked the line cuz it was causing the guage to go up and down really fast when there wasnt anything wrong in the motor but the switch went bad and it was leaking from the sending unit thing. Sounds like something is blocking the lines in the TB.. /forums/images/graemlins/truck.gif /forums/images/graemlins/usaflag.gif www.zombieoffroading.8m.net
     
  5. HarryH3

    HarryH3 1 ton status Author

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    It could be a bad module in the distributor. It sends a signal to the ECM that tell the ECM when to fire the injectors. If that signal stops, then the injectors turn off. You'll need a wiring diagram and a meter to check if the signal is bouncing like it should be when the engine is being cranked.
     
  6. DaveCowley

    DaveCowley 1/2 ton status

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    I know it sounds funny but mine did the same thing after putting in a reman engine and we checked everything from fuel pump to oil pump to fuel pump relay and none of it was the culprit. It ended up being the vacuum routing and I had a massive vacuum leak so the map sensor was shutting the engine off. Check your vacuum routing diagram. Make sure that it is right and that there are no vacuum leaks.

    Dave Cowley
     

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