1998 k1500 5.7 Misfire at Idle

[zbodie]

I have a 1998 K1500 5.7 that has a rough idle. Looking at data from a OBD2 code reader it is missing on #7 cylinder. It does not do it while driving only at idle. The truck has had the MPFI to the CSFI. The CEL is not on. You can feel the misfire and the exhaust is rich smelling of fuel. I changed to plugs, wires, cap and rotor on it thinking they may be an issue, no change. I have checked the CMP position and it is around 9.6 @ 1,200 RPM . If I adjust it to get it down to the 2 to -2 range then it misfires on #4 and #7 cylinder. I am thinking possibly the distributor gear is worn causing the issue. Any input is appreciated. Thanks.

 

[Schurkey]

Verify distributor gear, back-of-the camshaft gear that drives the distributor gear, and timing chain slack.

Vacuum leaks tend to be more noticeable at idle compared to higher RPM.

4 and 7 are companion cylinders, firing one crank revolution apart. I don't know if that's somehow significant.

"Rich-smelling" exhaust is usually an indication of 1) misfire, and 2) the catalyst is very, very unhappy.

 

[zbodie]

Thanks for the input. I have done a smoke test and didn't see any smoke for a vacuum leak. That was one of my firat thoughts on it running rich, until it started showing a misfore pending code. It only shows when it sits and idles for along period of time. I plan on pulling the distributor in the next few days and looking at the gear. I was leaning towards the distributor gear next, but figured I would ask on here before I started that project. Thanks

 

[zbodie]

Finally got around to replacing the distributor on my truck. That was a pain to say the least. It did fix my misfire issue though. I am able to set the CMP Retard to 0° and the engine idle without misfiring. Exhaust still smells a little on the rich side, but the misfire is gone for now. Thanks for the advice.