Need help with this !!please!!.............. i have a 1996 Chevy Tahoe 5.7 with 180k......... It was mixing Coolant with Oil.....So........... I took the Intake off to start a Head job on it thinking it was a Head Gasket but when i got the intake off.... It was obvious that the intake Gasket was shot..... so i re-assemble the intake and got the Coolant and Oil Mixing stopped.......... The Truck runs ok, dont overheat, and again no Mixing fluids,......BUT!!! it has a #4 missfire.....Changed the spark plugs Cleared the Code and Engine light came back,..... same code.... The truck runs good like on the Highway but under load you can feel the missfire....also standing in drive on a stop you can feel the miss.....Please ,...... i need help before i take the heads off ...... .for no reason..... I did a Comp check on that cyl and that was good 125..... I'm just thinking could it be a Valve and not a head gasket,....i'm not lossing coolant at all after the intake job.....Thanks for your help.....

You may have a problem with the poppet valves under the intake manifold. These are the mechanical injectors. This system has alot of issue with misfires and fuel leakage. Also when you took the large plug off on the center of the intake you may have misalighned the fine connector pins. Check them and hope this helps.

You probably have a plugged poppet.This would be the injector.The only thing you need to take off is the upper intake plenum.You can get them separate,you don`t need to get the complete spider assembly.They are known for clogging up.They are also known for the intakes leaking and mixing with the oil.I would not take the heads off.You can try putting in some injector cleaner but it could take a while depending how bad it is clogged.You can also take it into a repair shop that has and injector cleaner.These work very quickly and will usually take care of the problem almost instantly.Let me know what you find.Good luck.

I'd say that if it's intermittent it could be the plug or the wire, not something internal. It wouldn't be the first time I've seen a defective plug. I'd be willing to bet that it's an electrical issue in the firing system. If the plug is new take it back and get another. Then check the wires in the dark to look for splits or cracks. Double check the distributor.