Need help with trouble codes, engine misfire

I'll give ya a quick rundown on the XJ. Its a 1997 with a 4.0 and a Manual. About a year ago it overheated and warped the head. We got a head job done on it and and all put back together. Right after that the clutch went out and in the process of replacing it we yanked the wires out of the CPS. Got that all done and replaced the CPS. It ran and still runs perfectly fine but has had the check engine light on since we redid everything. We got the codes pulled, which I will list below. They mainly all have to do with misfires except one says it is not getting a Crank position signal at the CPS and that one has me stumped, well they all do because it runs perfectly fine. As far as the head goes, they had to mill it back flat and said they had to take a pretty good amount off to get it back flat. The only time it "misses" is if your in say 3rd at about 3,000 rpm and stomp the throttle it has a hesitation or "miss" and then takes off like it should. Im wondering if it had something to do with compression numbers rising or if it messed with the timing because they milled the head and maybe that is causing it. Any input would really be appreciated, I will posted this over at JeepStrokers to see if anyone over there knows as well. Here are the codes...

P0300 - Multiple Cylinder Mis-fire
P0301 - CYLINDER #1 MISFIRE
P0302 - CYLINDER #2 MISFIRE
P0303 - CYLINDER #3 MISFIRE
P0304 - CYLINDER #4 MISFIRE
P0305 - CYLINDER #5 MISFIRE
P0306 - CYLINDER #6 MISFIRE
P0320 - No RPM Signal to PCM (Crankshaft Position Sensor Signal to JTEC) - A CKP signal has not been detected at the PCM.

Thanks,
Tom

Not sure what to think about the P0320. If a crankshaft sensor truly isn't detected, your engine is NOT going to run and your engine is running.. Have you tried clearning all the codes and seeing what comes back?

Could be a vacuum leak causing misfires across the board I suppose.You're looking for a "common cause". You have all cylinders misfiring so you can safely rule out things like a bad plug or injector, etc.

Always review tuneup hardware when symptomatic though. Plugs, wires, cap, rotor, test ignition coil for resistance.

If you don't stumble onto it, I'd seriously consider putting this on an engine analyzer/ignition scope. In the right hands of someone that knows how to run it and interpret it, that technology can be invaluable in tracking down this type of stuff....

Good luck and be sure to keep us posted.

If it wasn't missing those codes would have cleared themselves by now. The computer uses the crank sensor quite a bit to determine if the motor is missing so with that code stored your problem may lay there. Clearing the codes is still a good idea. My guess is p0300 will set first B/C it usually does, it is more general than the others. What code comes next will tell you more. I will run this over on Identifix and see what comes up.

I think you probably have a bad crank sensor. It is a high fail rate item on a 97. I would still clear the codes and see what pops back. I see in your initial post you replaced it. The connector for the crank sensor has been known to cause problems. I have had 4.0's come in for a no-start and just touching that connector will fix them for awhile. Wiggle that connector with motor running and see if motor skips.

I kinda figured it had to do with the CPS. When we did the head we replaced all the general tune up stuff, minus the coil... This Jeep belongs to my dad, our 4th XJ all together. My first used to have CPS problems, 90 Renix, and when it wouldnt start just unplugging it and plugging it back in would generally get it running. I am on the road right now but as soon as im home I will check the plug, be home next week. It has to get passed emisions so I told him I could just stop next door, disconect the battery to clear it and run it through before they pop back up if need be. Disconecting the battery will totally clear them correct? If not I might just swap the CPS from my XJ on to his to get it through... Really appreciate the help with this. Sure hope I dont have to buy another one of those things, $$$.

That won't work here in Md. When you clear the codes you have several emisions monitors that your computer has to reset. It goes through a series of tests on the emisions system and when it is satisfied with results of each test run it will turn off each monitor. Here in Md. you have to drive the vehicle around until all or most (depending on model year) of the monitors have reset. This can take a couple hundred miles.
Not sure how they do it in your neck of the woods.

Problem solved, Registered the Jeep at my new address... No emissions. Hahaha