Thread: Intake backfire

  1. Intake backfire

    Hey all,
    Ihave a 88 yj 2.5 tbi...i check the timing chain and set the distributor its pointed at 1...im still getting fire in the tbi....it wants to idle but then it pops every so often threw the tbi...and suggestions?

  2. #2

    Re: Intake backfire

    Valve intermittently sticking open? Premature detonation of air fuel mixture? Unplug a spark plug wire and see if it stops popping through the TBI. If it doesn't, plug it back on and move on to the next plug wire and so on until you can determine if the popping is particular to one of the cylinders.

  3. #3

    Re: Intake backfire

    could be a vaccume leak causeing the computer to turn back the ignition piont . my wifes truck had a bad intake manifold gasket sucked air, computer read it as lean and pumped in more fuel it also turned back the ignition to the point it would stumble and die .... it was an 01 ford f150. i hate fords
    88 yj sahara, SBC 350/TCI MAXIMIZER TH350. Rubicon Express 4.5 extream duty lift. Edelbrock AVS 4x4 carb 3" body lift. SmittyBuilt rock crawler front bumper. Hurst Pro-Matic 2 shifter. And a bunch of other stuff.

  4. #4

    Re: Intake backfire

    Cool Guys Thanks Ill try those things and post what i come up with.

  5. Re: Intake backfire

    What actually happened to my engine when it done this was a valve push rod came unseated and was laying inside the valve cover. I just reinserted the push rod and made sure that it was functioning and tightened everything down. A forgotten step when I had worked on it previously. But it was very annoying and had severe power loss.

  6. #6
    Join Date
    Feb 2009
    Location
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    5,609

    Re: Intake backfire

    Do you have any codes? Check plugs, make sure the gap is correct. Check wires and distributor cap and rotor for carbon. After that you could check for sticking valve.

  7. #7

    Re: Intake backfire

    Check your Valve Timing..Here's the Procedure.

    Disconnect the spark plug wires and remove the spark plugs.
    Remove the engine cylinder head cover.
    Remove the capscrews, bridge and pivot assembly, and rocker arms from above the No.1 cylinder.
    Alternately loosen each capscrew, one turn at a time, to avoid damaging the bridge.
    Rotate the crankshaft until the No.4 piston is at top dead center (TDC) on the compression stroke.
    Rotate the crankshaft counterclockwise (viewed from the front of the engine) 90°.
    Install a dial indicator on the end of the No.1 cylinder intake valve push rod. Use rubber tubing to secure the indicator stem on the push rod.
    Set the dial indicator pointer at zero.
    Rotate the crankshaft clockwise (viewed from the front of the engine) until the dial indicator pointer indicates 0.305 mm (0.012 inch) travel distance (lift)
    The timing notch index on the vibration damper should be aligned with the TDC mark on the timing degree scale.
    If the timing notch is more than 13 mm (1/2 inch) away from the TDC mark in either direction, the valve timing is incorrect.
    If the valve timing is incorrect, the cause may be a broken camshaft pin. It is not necessary to replace the camshaft because of pin failure. A spring pin is available for service replacement.

  8. #8

    Re: Intake backfire

    ok here an update. i put a pressure gaudge on each piston..1,2,4 are 165-170....#3 is around 130 and is the one firing into the intake...i still havent check the valve timing...i need to get the tool you mentioned...i found that the crank shaft sensor had a missing bolt and was out of alignment..replaced that no change...i pulled the valve cover and put a straight edge across the valve springs...the were all level so i believe they are seating...tore it to the timing chain and that all looked good...and i hve timmed it the best i could...its firing tdc on 1

  9. #9

    Re: Intake backfire

    Quote Originally Posted by ThorBuilt1 View Post
    ok here an update. i put a pressure gaudge on each piston..1,2,4 are 165-170....#3 is around 130 and is the one firing into the intake...i still havent check the valve timing...i need to get the tool you mentioned...i found that the crank shaft sensor had a missing bolt and was out of alignment..replaced that no change...i pulled the valve cover and put a straight edge across the valve springs...the were all level so i believe they are seating...tore it to the timing chain and that all looked good...and i hve timmed it the best i could...its firing tdc on 1
    Bad valve or a bad valve seat.

  10. #10

    Re: Intake backfire

    im goin to pull the head tomorrow and look at it...ill get back to you on it...thnx for all the help

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