Help with misfire issue, in depth explanation.

[Cvldwell]

Hey guys, I understand that this issue is constantly beaten to death but I'm at my wits end and need some help.

I have a 1997 XJ with 212k on chassis and 98k on the replacement 4.0 (done by P.O) that's having some issues which I've researched the hell out of and repaired most of them, to no prevail.

The Jeep starts easily, runs fantastic for a minute or so, then begins with typical bouncing idle, misfiring, sputtering and stalling. I can keep it alive in park/neutral just fine but if I give it much throttle input under load, starts pinging and cuts power. I get no CEL.
Here's what I've done and replaced to try to remedy the issue:

- New ignition coil, cleaned grounds to block.
- Checked plugs and wires for spark
- P.O had replaced the cap and rotor which I went through anyways and cleaned the contacts, dizzy also appears to be indexed properly, haven't checked cam sensor. Don't think it would run as well as it does (momentarily) if it was 180* off.
- Replaced the infamous cracked exhaust manifold and gasket because I thought maybe it was sucking in unmetered air and throwing the AFR off.
- O2 sensors are good, relatively new and again, no CEL's.
- Replaced the crankshaft position sensor with MOPAR, it had low resistance but replaced anyways in the event of a thermal short or similar. The one I pulled out reads anywhere from 550-740+/- from pins B to C and the MOPAR reads the same. On this topic, it cranks and feels like it hits a rough spot briefly then pulls through and starts right up.
- Cleaned and checked voltages of MAP, TPS, IAC & all related.
- Checked vacuum lines
- Checked voltage and resistance on almost every wire possible however don't have much knowledge of the PCM and didn't go too far into it. Don't know how to go about checking the ASD.
- Cleaned every connector with wire cleaner.
- Checked and cleaned grounds
- Checked all fuses and relays
- Checked fuel pressure and fuel leak down (it's at a strong 48psi and doesn't leak down for hours)
- Compression is good, tested around or above 140.
- Probably quite a few more things that aren't coming to mind at the moment.

Have NOT looked into the clock spring/cruise cont shorting issue. The cluster doesn't typically work upon startup but works if I bang on the bottom and top a couple times, airbag light will illuminate when gauges aren't working but goes away after banging on it and gauges begin working.

If anyone has any suggestions that would be great. I'm mechanically inclined but I feel like I just need a push in the right direction or someone to spark the lightbulb on whatever I'm overlooking. I've done all I can at this point.

 

[DieselSJ]

Distributor is 1 tooth off.

 

[Cvldwell]

I'll give that a shot, thanks Diesel.

Anyone else able to comment on that or further?

 

[8Mud]

If your distributor is lined up correctly, a bad O2 sensor may not throw a code. Mine didn't set a code on my 96 until it was completely dead. It was acting up for months before it eventually died completely. My O2 sensor was around six months old and I was assuming my issues were something else.

Mine ran fine for about a minute then would stutter and sometimes stall. Sometimes at an idle it would start running really rich and sounded a lot like a bad CPS, miss, lugging, stutter, stall. Restarting a hot motor was a crap shoot, sometimes it was OK, other times it would run really rich, to the point the motor barely ran at all. I really wasn't aware a bad O2 sensor could cause all this grief, it was a first for me.

 

[Cvldwell]

Cool thanks Mud, I'm doing the timing as we speak and if that doesn't fix it, I'll look to the o2's. Which one would be the better of the two to start with? Don't want to buy both if I don't have to ya know?

 

[8Mud]

The front has most of the input. As far as I know the rear is mostly fine tuning the fuel air ratio so the CAT can do it's thing efficiently.

Before you buy a new O2 sensor clean the connector good, check the wiring where it runs up the front of the motor to make sure it isn't cooking on the exhaust manifold and check your O2 sensor heater fuse. I cable tie that wire well away from the exhaust manifold just in case.

You may want to also crawl under the rear and make sure the wires on the rear O2 sensor didn't come loose and cook on the exhaust which can cause some weird computer issues if you get the 12 volt heater wire melted to the O2 sensor wire. I've torn my rear O2 sensor wires off twice (fuel pump once) and pulled the cable clamp loose once allowing the O2 sensor wires to cook in the exhaust. Dried branches in tall grass on overgrown farm roads can be hard to spot and often find there way into undercarriage wiring.

And while my mind is in cable meltdown mode , check your CPS wires for melting onto the exhaust manifold also.

 

[Cvldwell]

*Solved*

It was the distributor off by a tooth, as Diesel stated.

Thanks guys! I should've gone with my gut and checked it before I threw $400 worth of parts at it. Oh well.

 

[DieselSJ]

*Solved*

It was the distributor off by a tooth, as Diesel stated.

Thanks guys! I should've gone with my gut and checked it before I threw $400 worth of parts at it. Oh well.

Sweet! I'm glad my suffering years ago was able to help someone.