1999 Chevy Tahoe. Slight misfire at 750 revs, hard shift 1st and 2nd.
I have replaced cap, rotor, wires, plugs, MAF, air filter, cleaned the ERG and had the transmission checked (they said it was fine). In Park it is ok at 500 revs, but if you increase it to 750 -1000 there is a noticable vibration in the cab. On the road there is a slight hesitation at around 35mph (again about 1000 revs), I have had occasion when once warm there is a hard shift 1st and 2nd, and aoocasionally with cruise on, it seems like it cant make its mind up what gear it wants. As the stutter occurs in park I assumed it was not the tranny, I may well be wrong.
No codes, the only time it did throw a code it was P8070, but that was a while back and it hasnt thrown that again. Any ideas?
The backfiring could be caused by an improperly set air gap on the crank position sensor. It could also be the timing not being advanced properly under acceleration.
I'm unable to find a P8070 trouble code. The closest I could find is P1870 and that says that a transmission component is slipping.
June, 28, 2011 AT 10:29 PM
I am sorry, I mis-typed the code, yes it was P1870, however, it doesnt backfire, more of a very slight mis-fire at around 750revs, and the hard shift when warm.
June, 28, 2011 AT 11:14 PM
Ok. Check the plug wires. They should have no more than 30Kohms of resistance. Make sure they are properly seated on the coil tower(s) and the plugs. Try to keep them from physically touching metal parts as much as possible. If your engine has a distributor, remove the cap and check to make sure there is no arcing between terminals.