94 Suburban

After giving my 94 1500 2wd suburban a badly needed tune-up in which I replaced the alternator, battery, plugs, plug wires, Belt, Distributor, Cap, rotor, and a new starter. She ran like a dream for 3-4 days when the
missing and backfire came back and started acting like nothing had been done. I then tightened the throttle body plate and checked all the hoses for obvious leaks and connections for the many sensors. Rechecked timimg, checked fuel pressure and read 13lb as spec. Compression is 110-125 lbs all around. All that seemed well. I replaced the plugs again with new AC Delco and the rig ran like a champ again. Its been one day since this last work and the missing is coming back again fast. The missing is coming under any type of load. I pulled the plugs again and they dont look that bad accept #5 is carboned-up.
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Sounds like a bad intake gasket sucking oil from the lifter valley! I have had similar problems on a couple engines. Could be something else, but it sure rings familiar!

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Well, you may be right shades, I have considered a valve seal problem also. I guess the next step is to do a complete compression check/troubleshoot with all the plugs out and the engine warm to see if anything else is wrong with the valves or rings. I dont want to tear into the engine manifold gaskets and find the seals or rings are bad and have to do it all again. Maybe its time for a new rig.
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Intake gaskets are cheap and it would give you a look into the lifter valley to see how clean your internals are. If you are gonna trade it off, it will bring substantially more running right.

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i had the same problem with my 91 and it turned out that one of the spark plug wires was bad. when my truck was in park idling we pulled each plug wire and no 5 was arking before we even touched it.
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