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Thread: 4.3 bogging down/backfiring from engine.

  1. #1
    IlluSive XpecTaionS l1ld3v1lrydr's Avatar
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    4.3 bogging down/backfiring from engine.

    This has been driving me nuts. I can't seem to find the cause of the problem! Some shops have told me it was a vacuum leak, some say it's in the distributor.

    It's on a 93 4.3 W code vin, 220,000 or so miles. Seems to do this more so when its cold/raining/snowing out than when it's warmer. But while driving, the engine just bogs down and starts backfiring from under the hood on the driver side (so it sounds). So I give it a little more throttle to stay up to speed and then after its done acting up, it just takes off like nothing's wrong.


    I've check fuel pressure as well as listened for the pump to prime. Thats all good. I just replaced the fuel filter along with the spider injectors. Plugs are new, has 8mm Taylor wires on it. Rebuilt the distributor cap along with the Accel Cap/Rotor pack and readjusted the timing (unplugged brown wire under the dash) Has a MSG Blaster coil pack. I've also replaced the TPS sensor. Nothing has touched my problem.


    The CEL will come on for maybe 2 minutes here and there. But not always when it's acting up. Just pulled the codes and one was "13 Oxygen sensor or circuit", and one of the ones from the time before when I pulled the codes was either "34 Manifold Absolute Pressure (MAP) sensor signal voltage low" or "34 MAF (Mas Air Flow) sensor or circuit". But the MAF is good, replaced with another working one, didn't change anything.


    Any idea's one what the hell to check!? I'm running out of patience lol
    :tongue: w1shf00l th1nk1n' :boink:

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  2. #2
    I'm BATMAN! Harley's Avatar
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    Make sure all the connectors are seated well and sealing too. I had similar problems on my 2.8 when I didn't plug the MAP in all the way. Also caused myself a no start situation after washing the engine bay and getting the oil pressure switch wet. I'd start with the MAP and MAF and check for water intrusion. If there is any blow it out and keep a look out for a new plug or seal for the plug.

    Do the same for your O2 like the codes are telling you. May want to see how much one costs and replace it while you're at it. It is one of the things you haven't replaced yet from what I was reading.
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  3. #3
    Zombie Killer 6SpeedBlazer's Avatar
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    put an OEM coil on it and ditch the MSD pos coil.

  4. #4
    IlluSive XpecTaionS l1ld3v1lrydr's Avatar
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    I switched back to the OEM coil, and that didn't make any differences so I put the MSD back on. I haven't messed with the O2 sensor yet. And I did just go over all the sensors on the top of the motor and they're all seated properly and I don't see any issues with those.


    I forgot to add that it doesn't like to start in the mornings or if its been sitting for a few hours. It cranks just fine, but just doesn't wanna turn over. And I've found that if I just tap the ignition (key) forward instead of holding it forward, she's more likely to start that way, but it will pop under the hood and then runs like shit til it comes up to idle.
    :tongue: w1shf00l th1nk1n' :boink:

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  5. #5
    5.7L VORTEC 350 blazin4low's Avatar
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    i had a similar problem on the '02 xtreme, it was the o2 sensor.

    On the '93 the o2 should be on the driver's side, possible giving that side the problem, the xtreme was the passenger side and that's where the o2 is.

    I believe for the older models the o2s are cheap
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  6. #6
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    i doubt its an o2 doing this, cant rule it out, but it usually doesnt have enough effect to be that severe.

    it wouldbe alot easier if you could see the data from your ecm.


    fuel pressure, did you have a gauge taped to your windshield when you drove, and when it acted up? pressure at idle isnt going to tell you everything. ALso need to check the volume.


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  7. #7
    IlluSive XpecTaionS l1ld3v1lrydr's Avatar
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    I hooked it up to a Snap On scanner my buddy left me borrow. Picked up a faulty O2 sensor code, and upon driving it, it kept going back and forth between rich and lean. Other than that, everything checked out normal. Though it wasn't doing the whole backfiring thing when we drove it hooked up. Has only been doing that in the mornings.

    I drove the blazer for months with a leaky injector (the one against the firewall on the pass side) and the O2 sensor is on the passenger side right before the cat. Bought a new one last night for $45 from advanced, direct replacement. But couldn't break the old sensor loose. Had the special little tool, breaker bar and the torch on her, and she still wouldn't budge. Didn't wanna fudge anything up to terrible bad so I left it be and dropped it off at my exhaust guy tonight. He's gunna cut that section out, and weld in a new piece with a bung for the new sensor and reinstall.


    Hopefully that will take care of some of my problem. I'm sure it can't be to good for as long as I drove it with gas pretty much dumping out the exhaust. And yes, I've replaced the plugs since replacing the leaky spider injector lol.
    :tongue: w1shf00l th1nk1n' :boink:

    4 door love... or... love-in the 4 door... :bigthumb:



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