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Thread: 96 z71 backfire

  1. #1
    Join Date
    Oct 2011
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    96 z71 backfire

    OK here's wats up...
    I got a 96 k1500 z71 with the vortec 5.7 BS.
    My check engine light came on so I took my code reader and scanned it saying random misfire, so I cleared the code to see if I could get it to come back on which it did, so while I was at work I got a code reader that noone Uses anymore it showed nuthing and check engine light went off. Well on the way home about 25 miles the check engine light started flashing it started backfiring on the passenger side. The next day I figured it was the common vortec problem with the spider injectors it wasn't. I changed cap rotor plugsan wires, ran fine around 20 minutes. I found it had low compression so I pulled the heads they were warped one was worped. 05 and one was warped. 06 and had 12 leaking valves.Well I got new valves and both headed resurfaced put everything together and it ran like hell for a month and a half. Then the backfiring and missing started again, accept this time it was the other side the machine shop said that the deck was probably uneven on the block so I need a new motor. Well I bought a 97 c1500 drove it home 30 miles pulled the motor out and stuck it in my truck only thing I did to it was new intake and gaskets and put my chrome valve covers on it stabbed it in.. the truck is still backfiring on the drivers side check engine lights still flashing and all... I changed everything on it. I took the cats and sensors off the other truck put em on mine and still didn't help...
    can anybody help?
    Only thing left is when I hooked up that old code reader is maybe it messed up the computer right? Could it be the computer?
    Any advice is greatly appreciated!!

  2. #2
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    this is my cousin fellas. im not sure if any1 here knows anything about 5.7s but we cannot figure out anything of what is wrong with it.... any help is greatly appreciated...

  3. #3
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    I would check the intake gasket installation. If that is the only thing you changed on it. Especially if your old motor backfiring switched sides after the head refurbishing.

    What crank sensor did you use? New or old?
    Last edited by tanz45; 10-20-2011 at 09:22 AM.
    2013 CC 5.3
    81 C10 LS1 project

  4. #4
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    I used everything off of the parts truck absolutely eveerything... I also put the maf sensor on too

  5. #5
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    How did you set the Cam position retard when you replaced the intake?

  6. #6
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    I set the timing back to the way it was if that's Wat ur asking? I set everything the exact same way it was and used every sensor and everything off it
    Last edited by bigazz71; 10-20-2011 at 01:17 PM.

  7. #7
    Join Date
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    Quote Originally Posted by bigazz71 View Post
    I set the timing back to the way it was if that's Wat ur asking? I set everything the exact same way it was and used every sensor and everything off it
    This is the key question to troubleshoot your problem. It seems as if most likely your backfiring on the replacement engine is being caused by a different cause than what your first one had. On our vortec vin r's the timing cannot be zeroed out just by eying the factory yellow paint mark on the distributor and intake. You need a scanner that shows the timing while the est plug is disconnected over by the master cylinder. The cheaper scanners do not show this reading. The base timing should be as close to zero as possible. And when you make an adjustment by rotating the distributor you have to give the reading 30secs to stabilize. Lock the the dist. down when you get it near or at zero. Then recheck. Reconnect est wiring plug when done.

    Mine has 245k on it and ive replaced the intake gasket. Owned the truck since 82k. Never been a victim of the spider problem nor busted valve springs.

  8. #8
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    So your saying it sounds like a timing problem not the computer? I mean why would it have just started all the sudden when I pulled the codes. I was wondering if maybe it backfed into the computer somehow?

  9. #9
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    Quote Originally Posted by remauto1187 View Post
    This is the key question to troubleshoot your problem. It seems as if most likely your backfiring on the replacement engine is being caused by a different cause than what your first one had. On our vortec vin r's the timing cannot be zeroed out just by eying the factory yellow paint mark on the distributor and intake. You need a scanner that shows the timing while the est plug is disconnected over by the master cylinder. The cheaper scanners do not show this reading. The base timing should be as close to zero as possible. And when you make an adjustment by rotating the distributor you have to give the reading 30secs to stabilize. Lock the the dist. down when you get it near or at zero. Then recheck. Reconnect est wiring plug when done.

    Mine has 245k on it and ive replaced the intake gasket. Owned the truck since 82k. Never been a victim of the spider problem nor busted valve springs.
    That is what I was referring to, but you are confusing the procedure with a TBI engine a little. There is no plug to disconnect on the Vortec engines. You are right though, you need a scanner that will support enhanced GM data to do it. I've asked HPtuners to add this PID to their scanner, but I don't think it has ever made it in.
    The timing is not adjustable, and there is no other way to properly set this. Making a mark and realigning it is not accurate enough.
    Engine should be at operating temp, start scanning. RPM has to be over 1000 to get an accurate reading (which the scanner can command). Then adjust the distributor to get the value within + or - 2 degrees of 0. I always shoot for 0, usually you can get it there.

    I have seen these out as much as 45 degrees by people doing the stab and pray method.

  10. #10
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    So I need to hook up a computer with live data pretty much?? And 0 the timing

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