I have recently had my 4.3 rebuilt in my 99 bravada. It ran great for awhile. Now every morning when I go to take off it misses. Once in awhile it pops a miss fire on #4 cylinder. It runs ruff for about 2-3 miles then straightens out and runs just fine for the rest of the day, even after sitting at work for 9+ hours it starts back up no problem. Its just after it sets over night. I replaced the dist cap and it stopped for awhile now its back. Ive poured water over the engine thinking its a moisture problem and got no result. Iam out of ideas here. someone said it may be the timing cover, that the after market covers affect the cam sensor some times. anyone have any knowledge on this or any suggestions?

 

It sounds like a sensor issue, but the constant misfire on cylinder 4 makes me wonder what condition the spark plugs and wires are in.

 

I agree, check your plugs and wires. I had inadvertantly cracked an insulator when I pulled plugs for inspection. The misfire was at different operating ranges and was baffled untill I listened closely and could hear a faint snapping (arching) coming from the side of the engine that the bad plug was on. Replaced all the plugs and voila! I keep the cracked one as a reminder to always use a socket with an insert.

 

checked all plugs real well and didint find anything wrong. The wires and plugs are less then a year old and are top of the line plugs. I also agree with a sensor problem thats why i was curious as to if anyone else has had a problem with the aftermarket timing covers and the cam sensor. This seems to be at its worst after a nights rain. I have a recorded hooked up to it and now imagine that the check engine light will not come back on. only codes i get from it are cylinder 4 miss fire and random miss fire.....so stumped on this one.