Engine Misfire Mystery. Please Help.

[awalts]

I drive a '98 Tahoe 2DR 4WD with the 350 Vortec.

For a few weeks I've had the check engine light on. Code reader says it's a cylinder 4 misfire. Truck shakes pretty good when idling, and smooths out when over about 1200 rpm.

So far I've changed the spark plug, spark plug wire, distributor cap, and the rotor under the cap, and it's still misfiring. I also ran a compression check and it came back at 150 psi which is well within spec.

Failing to find the problem, I took it to a Chevy dealer. They couldn't find anything wrong either. Their suggestion to me was to do a tune-up, hence the new distributor cap and rotor (only part of a tune-up I hadn't already done).

Has anyone else had this problem? Anyone have an idea what I should try next?

 

[lesterl]

Has it had the new MPFI upgrade installed? Perhaps you have a missfiring fuel injector as the original Poppets do that...

 

[Zachaotic]

I have known cars, doesn't matter which brand seem to have issues with other brands of spark plugs in their ignition systems. I dont know why, but brother in law had problem with bosch in his 77 Datsun. Told him to change to NGK, fixed it. Friend of mine had a problem with his jeep after a tune up, told him to switch to champion-- same fix. It may sound silly but if its not what Lesterl says then I don't know either, hope that helps.

Try autolite, seems to work great for me.

 

[lesterl]

These dont play well with bosch, I have found that the OEM's and the NGKs work fine tho....