1996 k1500 4x4 5.7 automatic misfire mystery

Discussion in 'Chevy C/K Truck Forum' started by Randy_H, Oct 7, 2012.

  1. PantheraUncia

    PantheraUncia Epic Member 5+ Years 1000 Posts

    The only thing I did not see listed is have you checked the ground cables? (negative from the battery to engine ground and chasis ground) ? A bad ground can do allot of strange things.
  2. Randy_H

    Randy_H New Member

    I removed both and confirmed that they are not corroded and are tight. Sorry I didn't mention that before.
  3. Randy_H

    Randy_H New Member

    I took the dash apart to see if the radio just had a loose connection and if it was a separate issue. I can't confirm that yet...so far the radio hasn't reset to 1:00.

    Just for fun I cleared the codes and test drove......went about 1/2 mile and it started missing again check gauges light came on and the temp gauge was at 255 degree (just before red)....it almost choked off while I was turning around check engine light came on and it limped home. Hooked up the scan tool and temp reported was 180 degrees.

    I have a few calls out to see if any friends have a PCM.....I am afraid to use my c3500 with 454 as a test PCM without someone confirming it will work....I would rather blow $40 at a salvage yard for the known correct PCM.

    Tomorrow I am going to check the ohm's on the temp wire from PCM to sensor. I am also going to add a new ground wire just for my own peace of mind.
  4. Randy_H

    Randy_H New Member

    Try this on for weird.......

    I tested the temp sensor wire and could not find anything wring with it. So I decided to go change the new temp sensor in case new one was a lemon. Installed the new one (engine cold and not cranked all night and day) the in dash temp gauge needle went about 1/4 inch past the red 260 degree mark.....I tried to crank it and the check gauges light came on and it was very hard to start but it started and ran very poorly.

    I decided to put the old temp sensor back in just so I could move it out of the garage.
    temp gauge showed 100 degrees....it started right up and check engine light came on.
    I scanned the code and it was P0304.....I ran live data and cam retard was at -45 degrees.
    I decided to go ahead and turn the distibutor again and see if I could get it back near 0....I adjusted to 2 degrees.

    I let it idle for about 10 minutes then started and shut off about 5-6 times......the code went off and I drove it around the block 8 miles. No codes.....no misses.

    I am not happy...sure it runs but what was / is wrong with it. Hard to trust it.

    Sometimes I think I am talking to myself......I guess it is ok as long as I don't answer. Wait, I have been answering myself. hmmmm
    Last edited: Oct 11, 2012
  5. Randy_H

    Randy_H New Member


    Cranked it up and let it warm up today.....drove around the block a couple of times and it started missing again (I could feel it scan tool did not report it). No check engine light.

    I had a friend bring me a good PCM.....I changed it. Drove it to town and it missed the whole way there. On the way home the engine light came on with the following codes:

    I am going to replace the Ignition Control Module tomorrow.

    Anyone want to buy a truck? lol
  6. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    My code list suggests that P0341 indicates some fault in the cam position sensor circuit. I know you said that you replaced the CAMP and got the cam retard set right, but this code doesn't seem to go away. Assuming the new CAMP is good, I'd start checking the rest of the CAMP circuit for a break/loose connection.
  7. Randy_H

    Randy_H New Member


    soooooooooo........I am left with 1 code P0340 (cam retard is at -45 and it will not move no matter what I do)

    I have:
    changed PCM (from junkyard...same result with original PCM)
    changed entire distributor with a new one
    new plug wires
    new plugs
    new crank position sensor
    new temp sending sensors (both of them)
    new battery
    new ground cable
    new positive cable
    new spider injectors
    new thermostat
    new timing set (both gears and chain)
    new main fuse

    So after some research I have read that some GMs require a CASE relearn if you change the crank, CPS, or PCM.

    The question I cannot get answered is, did the requirement start in 1996 or 1998? Despite what people are telling me the PCMs for 96-97 are the same and the ones for 98-99 are the same but 96-97 and 98-99 are not the same. I have read that it started in 1996 and i have read that it started in 1998.
  8. Randy_H

    Randy_H New Member


    very long story short.....

    1. buy only GM replacement distributor (not the brand new aftermarket)
    2. align distributor correctly (which I did)
    3. remove both battery wires for 20 seconds and then hole them together for 10 seconds (yep, beats me but this is the only way I could get the PCM to reset from the -45 cam retard) GM mechanic told me to do it.
    4. connect a level 2 scanner (one that will read live data, specifically cam retard)
    5. start the vehicle, read the cam retard (it needs to be with 2 degees of 0)
    6. if the retard is not within spec shut the vehicle off!! (I did not.....this was one of the main failures for me)
    7. if cam retard is less than -2 IE -15 turn the distributor counterclockwise if greater than +2 turn the distibutor clockwise
    8. restart and check cam retard....continue to adjust but always shut vehicle off prior to distributor adjustments

    walla!! all codes gone (specifically P0340 which I had) and all power restored and running great.

    FYI: the proper initial distributor position can be obtained pretty easily
    1. turn motor to TDC (you can verify with timing slot on harmonic balancer and "V" cut on timing chain cover
    2. rotor button should point to the little 8 etched in the side of the distributor (you can only see it with the cap off)
    3. cap should end up with spark towers perpindicular to the motor line (crank)

    I know this may be more info than anyone wanted or wants......but if I could have come upon a couple of these steps somewhere, I would have been able to set the timing right the first time instead of the 50th. :)

    Also, throughout this post I put trouble code P0304 and I meant to type P0340.

    I would also like to thank O'Reilly auto parts and the 3 employees that helped me with a ton with parts and patience!!
    Last edited: Oct 18, 2012
  9. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    Thanks for that description. I had never heard the need to turn the motor off when adjusting the cam retard, so that could be good information for others who need to tackle this operation.
  10. Randy_H

    Randy_H New Member

    I know that's the main thing that caused my entire problem. I have never heard of such a thing.....on all of google there was only one mechanic that mentioned it. One mechanic even instructed to unplug some mystery wire under passengers side dash (brown or tan) but I couldn't find it.

    I tested the theory. I wanted to confirm the fix....and sure enough.....either distributor and or pcm combo I tried....if I follow the steps above no code.....don't follow the steps and code every time.

    Thanks everyone!

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