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4.3 startingproblem

Discussion in 'Chevy Trucks' started by staley52, Feb 1, 2003.

  1. staley52

    staley52 Member
    from Iowa
    Messages: 98

    I have a 1990 astrovan that I use for sidewalks that will not start cold with the timing set properly if you crank the dist advanced 30 deg it starts right up then back it off to the mark I made when I timed it runs great and starts if warm but when cold it cranks like there is no spark advance it and pops right off.

    already done

    new timing chain
    reman ecm
    cap, rotor, plugs, wires
    new o2 sensor
    swaped in complete dist out of good running engine
    and when timing I do set it in basic settings by disconnecting the signal wire to ecm per manual

    once started and timed it runs great:confused: :realmad: :confused:
     
  2. wyldman

    wyldman Member
    Messages: 3,265

    Either you have a knock sensor problem,or a bad ign module.If you swapped in a known good dist,you have eliminated the pickup coil.

    I would unplug the knock sensor,and try it.It will trip the check engine light after a few mins and set a code 43.But if it starts OK,then that is your problem.It is in the side of the block,where the coolant block drain plugs are located.Usually pass side right above starter.Be careful with the plastic plug,they are very brittle.You kinda have to squeeze the sides and pull it off.

    If that isn't it,then it's most likely the ign module.

    It might pay to have someone throw a scanner on it cold,and watch the data.You will be able to see right off if it's a knock sensor,and how much the computer is retarding timing to verify the problem.

    BTW,if you do change the knock sensor,have a bucket handy,as coolant will come out.
     
  3. staley52

    staley52 Member
    from Iowa
    Messages: 98

    I will try that in the am I have a scan tool the MAC equivilant of the gm tech 1 but dont know the properdata blocks to watch on a gm as the only gms I work on are my own 7 to 5 I work on VW and audi and their ecms are completely different
     
  4. wyldman

    wyldman Member
    Messages: 3,265

    I don't have the mac,I have the snap-on,but you should still be able to do it.

    To check the knock sensor,you'll be looking for knock signal,or knock sensor voltage.If you see it high when cold,and dropping down when warm,then the knock sensor is bad.Some scanners will just show yes or no for the knock signal.It should read no all the time,until it senses a knock.You should also see a knock signal if you tap on the block with a ball pein hammer.

    You should also see a value for total timing,or timing advance.A positive value would indicate advance,and a negative value would be ******.

    Could you maybe have something knocking or rattling around when cold which is fooling the knock sensor into ****** the timing ? Just a thought.
     
  5. staley52

    staley52 Member
    from Iowa
    Messages: 98

    you said that if it is not the knock sensor most likly it is the ign. mod. but the module is in the dist. right?
     
  6. wyldman

    wyldman Member
    Messages: 3,265

    They have the pickup coil in the dist,but most of them the module is remote mounted,on the firewall,or sometime on a metal bracket above rocker cover.It is a black box,about 3x4x1/2" thick,with about 6 or 8 wires going into it with a weatherpack connector.
     
  7. Pickering snow removal

    Pickering snow removal Senior Member
    Messages: 151

    Fyi the ing module is mounted in the dist your elec leads going to the dist plug into the module , Ford uses remote module mounting in later years how ever gm keeps theres with the dist til dis comes about . if ecm is what your refering to its mounted under pass side hush panel
     
  8. wyldman

    wyldman Member
    Messages: 3,265

    Maybe i should have been clearer on what the module is that I was talking about.The 4.3L does use an internal module,and an external ESC module which uses the knock sensor input to control timing advance and ******.

    I would assume that his problem must lie in the module or konck sensor,or wiring,as he has changed\swapped the dist (which has the pickup coil and EST/HEI module),and the ECM.
     
    Last edited: Feb 5, 2003
  9. staley52

    staley52 Member
    from Iowa
    Messages: 98

    :(

    update sorry for taking so long, found that I did have a bad esc module replaced it system now works properly but to no avail with engine timed properly it will not start cold advance it 20 deg and boom fires right up I am about to put a lever through the dog house to move the distributer for startup:confused: help!!!
     
  10. wyldman

    wyldman Member
    Messages: 3,265

    Did you try disconnecting the Knock sensor ? It will throw a code 43,and turn the check engine light on,but if it is bad it should return the timing to normal,and allow the truck to start.I may have been incorrect on the knock sensor location,on older trucks it was located in the block drain plugs,left or right side.Newer trucks are up behind the dist beside the oil pressure sender.

    One other thought could be the PROM.Did you replace it when you did the ECM ? The ECM uses the PROM for baseline data,so maybe it's toast and telling the ECM to cold start with the timing ********.An updated PROM is always a good idea,as they work out a lot of the bugs with newer revisions,and they are usually real cheap.

    Did you ever get a look at the actual timing values with the scanner ?
     
  11. staley52

    staley52 Member
    from Iowa
    Messages: 98

    I was unable to watch the timing values but I did unplug the knock sensor once to try starting it.

    I did not replace the prom the reman ecm has my oem chips in it.
     
  12. wyldman

    wyldman Member
    Messages: 3,265

    I would try a PROM then,what else could it be ?
     
  13. Willie

    Willie Member
    Messages: 32

    Does it have a timing sensor?
     
  14. staley52

    staley52 Member
    from Iowa
    Messages: 98

    installed a new prom and IT RUNS :drinkup: :drinkup:
     
  15. wyldman

    wyldman Member
    Messages: 3,265

    WooHoo ! Great to hear you got it fixed.Sometimes you just gotta work through it one part at a time.