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Truck won't start

Discussion in 'The Garage' started by 1979jimmy350, Nov 24, 2006.

  1. 1979jimmy350

    1979jimmy350 1/2 ton status

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    I have been trying to get my truck to run for some time, i have had it running before and now i have no idea why it will not run, I have done the basic tests it has spark, fuel pump but no injector pluse, I thought it was the computer after some trouble shooting but it still will not run with a new computer, this is really confusing me i have never had a weird problem like this one before
     
  2. diesel4me

    diesel4me 1 ton status Premium Member

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    cood bee

    If it has spark and the fuel pump is working,it might be the ignition module--it controls the injector pulse as well as spark,and only one half of it might be working--Seen this a lot on 90's trucks..a crank sensor or pick up coil also can kill the injector pulse,but usually on TBI trucks when they fail,the fuel pump wont energize either...the computer is the last thing to blame,but can be faulty too..replace the cheapest part first,the module!..:crazy:
     
  3. chvymudin3388

    chvymudin3388 1/2 ton status

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    i thought that the module only controlled the spark order but i may be wrong but it wouldnt hurt to change it.
     
  4. diesel4me

    diesel4me 1 ton status Premium Member

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    nope..

    The newer TBI trucks have a module thats got several pins,more than the usual 4 on an HEI module ..it controls both spark and injector pulse,in union with the pickup coil or crank sensor ,depending on the year...

    My friend saves "good used" modules from junkers he's going to scrap--many times when a "dead" GM truck is towed in and there is no injector pulse ,or spark (has one but not both),swapping in a used module fires it right up in 90% of the cases...other 10% ends up being corroded wires or blown ECM or IGN fuses,or the crank sensor or pickup coil,or the fuel pump or relay....
    ...he's replaced a good many fuel pumps in the past,only to find it was the module or the other causes listed..now he checks everything else FIRST!..I didn't realize a bad crank sensor will cause the fuel pump not to function,I guess its wired into its power curcuit..took us awhile to figure that out!..:doah:
     
  5. 1979jimmy350

    1979jimmy350 1/2 ton status

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    i was thinking that it might be the modual, i had the orginal tested and it tested fone but i put a good working one in just to see and it changed nothing
     
  6. diesel4me

    diesel4me 1 ton status Premium Member

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    hmm...

    Time to start checking the other things then...I'm not well versed in how to do it,my experience with newer 88 and up trucks is limited to what I watch my friend fix in his shop--I like antiques better!..he usually tries the module first,then checks fuses and the relay for the fuel pump..if that doesn't make it run he starts replacing the crank sensor or pickup coil,because he lacks the test equipment to test them..thus the reason for keeping spares!..

    You check the fuel pump pressure??..if its low,the truck wont run,even though the pump might be running,it could be worn out and not putting enough pressure out...but if you have no injector pulse,its probably a wiring problem,etc..good luck,I know these problems suck to diagnose sometimes..:crazy:
     

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