Truck died twice today...

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by texas99lb, Jul 24, 2009.

  1. texas99lb

    texas99lb Rockstar

    Well I was at office depot and I was pulling out of the parking lot and I came to a stop...I was going maybe 10mph and my truck decided to started right back up... drove fine, then I came to another stop light when I get down to 10mph it dies again..I am thinking my fuel filter is clogged up and not letting enough fuel pressure build up through the fuel line to get to the injectors and the truck dies...its doesnt bog down or anything or act like it wants to stay on it just dies..The reason for my fuel filter theory is it did the same thing the other day but it cut out and almost died but came back up to normal idle...truck purrs like a kitten except for this issue (and my exhaust leak)...I just want to get some opionions on this..thanks guys, I dont know when the last owner changed the fuel filter so I think it might be a good cheap remedy for this problem..
  2. yotchie

    yotchie Rockstar 100 Posts

    makes sense. since fuel filters are a cheap fix it would be a good thing to try. even if it doesnt fix it you still have a fuel filter that you know is good
  3. bill190

    bill190 Rockstar 100 Posts

    There are many things to check and all of this would need to be checked by using a GM Factory Service Manual set for your specific year/model vehicle. (Order from or a GM dealer.)

    Also you would need a multimeter and fuel pressure gauge to do most of the testing.

    Anyway IDLE is controlled by the computer and the Idle Air Control Valve (IAC). Then the Throttle Position Sensor, when the throttle is completely closed such as at idle, signals the engine computer it is at idle. Then the computer takes over control of the idle via the IAC valve.

    So those are all very important things for idle. And if the throttle area is dirty and the throttle can't completely close, then the throttle position sensor would never be able to indicate to the computer that it is completely closed! Because it is partly open. Then the engine would not attempt to control the idle speed.

    So check the throttle body that it is clean and the throttle can completely close. Use throttle body cleaner only as this will protect any special coatings on the throttle body. DO NOT get any cleaning fluid on the electrical portions of sensors or valves as this can damage them.

    Also the engine gets part of its idle air from the PCV valve and associated tubes. So be sure those are clean and air can get through.

    Then test the Throttle Position Sensor with a multimeter as directed by the Factory Service manual for your vehicle.

    Then remove the IAC valve and clean inside where the valve moves in/out. DO NOT turn on your ignition with the IAC valve removed! This will shoot the pintle out of the valve and into your bushes.
    Crud inside there can keep the valve from moving in/out as it should. (It moves out for a faster idle.)

    Then test the connections to the IAC valve for ohms as directed by the service manual. And to see if it is working, the engine idle should be at factory specs for a cold engine and slower for a warm engine. Then if you turn on the A/C, the engine idle should go up a bit. This is the engine computer telling the IAC valve to open a bit to increase idle to give a bit more power to the engine for A/C. And when you shift out of park to R or D, the idle should go down a bit if you have an automatic transmission.

    If the above checks OK, then the factory manual would have other tests for various things. Go to the section which has this symptom and lists the checks to perform.
    1 person likes this.
  4. heavy chevy

    heavy chevy Epic Member 5+ Years 500 Posts ROTM Winner

    you could check the converter also this will make it die.
  5. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    Don't forget to check for trouble codes. One may have set and if it did it will save you hours of chasing ghosts. <G>
  6. texas99lb

    texas99lb Rockstar

    alright great..thanks for the recommendations, I appreciate it..looks like its me and the chevy today..Ill get back to your guys and let you know whats going on..thanks again
  7. texas99lb

    texas99lb Rockstar

    Well I cleaned out my TB today, it was pretty filthy..didnt look like the throttle plate was sticking open at all..I made it so clean I can see my reflection in it..I also bought a new pcv valve and installed that..I didnt get a chance to check the TPS. I have to go buy a multimeter tomorrow. I also installed a fuel filter..I drove up and down my street a few times and the truck didnt die at hopefully what I did fixed it, I will keep updating...
  8. bill190

    bill190 Rockstar 100 Posts

    Good! You are now ready for some "advanced" diagnostic testing...

    If you want to do a bit of "advanced" testing of the IAC valve, you can use my "Advanced IAC Valve Tester".

    Turn on the engine, then shut it off, and then the IAC valve "repositions itself" for starting. It extends all the way, then retracts half way.

    It does this because this valve "works blind". That is the computer sends it signals to move, but there is no type of feedback device to tell the engine computer that the IAC valve actually moved.

    To test it "by the book", you would need an expensive electronic tester because this is a "stepper motor" which needs "alternating pulses" of electricity to make it function.

    But you can hear it move! But only after the engine has shut off.

    The IAC Valve "listener"...
    Take a paper cup and put a small hole on the bottom, then thread a string through the hole, tie a knot then pull the string taught.

    Like half of one of these kids can or paper cup "string phones".

    Then tie the other end of the string around the IAC valve or the electrical connector attached to the IAC valve. Either of these would send the vibrating noise the IAC valve makes to the string. Then pull the cup/string taught and place it to your ear. Have someone else start the vehicle, then turn it off.

    You should be able to hear the IAC valve operating after the vehicle is shut off.

    Like this...
  9. texas99lb

    texas99lb Rockstar

    alright I will try that tomorrow...thanks for all your efforts man I really appreciate it..
  10. crayform

    crayform New Member

    Any luck texas99lb? I have a similar problem with my '94 Auto 5.7. At first it idled a little rough, then started to sputter when I took off from a stop. Now it surges when I start it and dies when I put it in gear.

    I replaced the cat with a straight pipe, and checked it when I took it out for loose or broken pieces that might be lodged in the rest of the exhaust - nothing. It was intact.

    I'm going out now to clean the throttle body and IAC. After that I'm looking at replacing the fuel filter and fuel pump. The truck has 153,000 and I'm swapping my stepside bed for a fleetside anyway, so I'll do the pump then...

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