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Thread: 96 z71 backfire

  1. #11
    Join Date
    Apr 2011
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    130
    Thats right pitch...its all coming back to me now. The EST (electronic spark timing) was on the x's firebird. Scratch the est plug from my above directions. Any automotive repair places will have a scanner with the enhanced data function. And yes it could be out enough to be causing backfires. I doubt its the pcm but anything is possible. I wouldnt rule out the ignition coil or the ignition module. More likely the coil...since usually when the module fails it dies totally and you get zero spark. Ive seen coils spit out sorry a$$ spark, intermittent spark and even once personally had a 1978 350 short the high side of the coil and actually energized chassis ground with the same voltage that was going to the spark plugs! Anything on the truck at chassis ground potential would knock you on your a$$ while the truck was running if touched!
    Try swapping ignition coil from your old engine only if the problem does not go away after getting that base timing zeroed out. Unlikely the pcm is the culprit but again anything is possible. The program can get corrupt in the pcm.

  2. #12
    Join Date
    Oct 2011
    Location
    brandon,ms
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    15
    I used the coil, ignition module, map sensor, maf sensor, and every other sensor off the parts truck I got which I drove home 30 minutes before I pulled it every sensors been changed and that's stumping me. I work at a shop here in Ms and me or anybody at my shop has never seen anything like it...

  3. #13
    Join Date
    Apr 2011
    Posts
    130
    Well assuming you didnt inadvertently swap in a bad part, I would start right off with zeroing that timing. Also check to make sure you did not get any wires stuck in between the block and tranny during the install. Make sure you got all of the original grounds hooked up too!

  4. #14
    Join Date
    Oct 2011
    Location
    brandon,ms
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    15
    Well today I zeroed in timing its dead on still missing on the drivers side... then I check my plug wires again they are all in order all 6 grounds are Hooked up I'm really leaning to electrical I also changed the plugs again on driver side in case maybe I had a bad plug and cylinder number 3 was pretty wet with gas could its same thing that it was doing with the old motor missing on 3 and 5

  5. #15
    Join Date
    Apr 2011
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    130
    You say you zeroed in the timing. Did you get ahold of an enhanced scanner and actually zero it in that way? Or? What was it at before any adjustments? Cylinder 3 was pretty wet huh. That is a clue. Since our vin r's have one ignition coil that fires ALL cylinders you can probably rule that out as a culprit. #3 spark plug wire, or the distributor cap (check #3 terminal on it) or it could have a crack near #3 terminal causing the misfire. Could be #3 injector is leaky also. Do a baseline compression check on all cylinders and see how #3 is compared to the rest. I go through a distributor cap and rotor once a year religiously! Thats just the nature of the beast.

  6. #16
    Join Date
    Sep 2007
    Location
    Broken Bow, OK
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    1,441
    Do the injector leak down test with the scanner to see if #3 is leaky.

  7. #17
    Join Date
    Oct 2011
    Location
    brandon,ms
    Posts
    15
    Wat I don't get is why would the injector be leaking now it wasn't when it was in the other truck but its the same way it was with the last motor. I used the injectors and all off the parts truck and the CEL wasn't even on had no miss or anything. I replaced the injectors twice with the old motor and it didn't help the problem at all and I Also replaced the fuel pressure regulator that didn't help either

  8. #18
    Join Date
    Apr 2011
    Posts
    130
    Hey, I understand you are frustrated. But throwing parts at it can get expensive. Work everything systematically and eventually you will get to the root cause. Just dont take any shortcuts on the troubleshooting. Anything is possible but my vin r is at 246K miles now and i have never had to replace the pressure regulator or an injector. I am sure they are getting pretty dirty but mine is just going to have to run until i get my 5.3l bored to a 5.7l put together and installed.

    Get away from the mindset that it worked fine on this engine so why would it be bad or it was ok last month so how could it be broke now. That will get you chasing your rear end and overlook a possible obvious cause. Ive been there done that...it dont work too good.
    Try something as simple as swapping #3 wire with a even bank wire and see if the problem moves to the other side or not. That plug being wet is a major clue to what is going on. I just think its highly unlikely that the computer is at fault because of our system being a one ignition coil ign system and you have only one cylinder with a wet spark plug.

  9. #19
    Join Date
    Oct 2010
    Location
    Pearl,MS
    Posts
    460
    he tried to zero it without a computer. i was there lol. he is supposed to go borrow a live computer from one of my dads buddies at car care and try to zero it in. i believe it is TIMING.

    2005 CCSB Silverado- 5.3
    Airaid CAI
    True Dual Exhaust
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    3.73 Yukon Duragrip limited Slip Diff.

  10. #20
    Join Date
    Sep 2007
    Location
    Broken Bow, OK
    Posts
    1,441

    Quote Originally Posted by NoTaTurBo View Post
    he tried to zero it without a computer. i was there lol. he is supposed to go borrow a live computer from one of my dads buddies at car care and try to zero it in. i believe it is TIMING.

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