1996 Jeep Cherokee 4.0L Timing (Flexplate HELP)

This vehicle runs rich at idle, -25% total trim. Cuts out and misses underheavy load, o2 reports lean. Fuel pressure is within spec; pump and regulator are new. (Vehicle originally had 70psi fuel pressure that would bleed down in 30 secs)

The timing sync pattern is way off. After checking the distributor and timing chain part of the system, I'm now suspecting the flexplate/ ckp operation.

Question is, anyone have any experience or tips to verify flexplate without pulling trans just to "take a look"? Also how the hell is this thing running? I did scope cranking compression with ign coil, seems TDC to me.. Maybe a clue?

I'll look for my good waveforms but you can take a look at one of my threads relating to cam crank timing for a 96 jeep. No distributor.

www.scannerdanner.com/forum/post-your-re...ase-study.html#23343

I found a known good pattern with an ignition channel like I had mine set up. The coil was firing on the fourth crank pulse, and my pattern lined up exactly. Combined with the relative compression test, this verified spark was occurring at true TDC.. So shifted flexplate ruled out. (Well in theory, because I couldn't find any documentation directly stating CKP is responsible for spark timing. but it made more sense than some algorithm using both cmp & ckp.)


The distributor was faulty. Bad part, probably out of the box. Specifically the CMP ring alignment. Ordered a new distributor to compare. Once it was set and timed properly, the rotor and cmp ring moved forward just enough to bring them back in sync.

Engine is still running rich, but no longer cutting out, hesitating, or bogging.