So lets recap----Its giving me a p0304, cylinder 4 misfire, and sometimes one about an very small evap leak. Basicly it starts fine then misses and runs real bad within a mile from where I leave from then if I shut it off and restart it will run fine. I changed the plugs ( copper core) coil rail, cam sensor, crank sensor, TPS, the ECM, swapped injectors around, did a compression and fuel pressure test, ran seafoam through it and lastly checked the index of the cam sensor. Still having problems

 

I dont think I have ever mentioned it but I think my XJ dose kinda have a miss when its cold, runs a little rough when I first start it up, and seams to run better when it gets to temp, this has alway done this and if it was a $30k car I would worry about it but I never did. So this could be related to my strange bad misfire??????

Ok now I was able to use both feet and drive home from work without letting it rev below 1500 rpms and it didnt misfire on me(beside the normal one metioned above) . Is there a sensor or somthing that only reads when ist cold or is in a closed loop ( dosent read ) until the jeep gets to a certain temp? I only drove a few miles keeping it above 1500 rpm then drove normal without issues. Hope this sheds some light on what up.

 

Can a MAP sensor be my problem even thou its not throwing a code?

 

It seems you've done a lot to resolve that misfire. I glossed over your post quickly so might've missed a detail or two...

I was going to question you on sensors but a quick look back reveals you'd been there and done that. I only hope that you got OEM sensors because the reliabilty of aftermarket sensors is untrustworthy. Nonetheless, you got them and they appear to function same as previous.

It is possible for your MAP sensor to be marginal but not bad enough to cause a code. Hand clean your throttle body and IAC using TB cleaner by hand just to rule out an stickiness. Also check for proper function of the engine temp sensor under cold and warm engine conditions (not the sender to the gauge or the electric fan trigger). I think it's at the back/top of the block on the driver's side and you need to check the output voltage - but don't take my word for it - look it up. Good Luck and let us know what you find.

 

I cleaned up the throttle body... no help. I do wish I would have spent the $ on OEM sensors but unfortunately didn't, although I picked them up from a small local parts chain that I have been shopping at since I started driving and never had any problems.

 

probly time to pull the valve cover and take a look!

 

Go ahead and take the look under the valve cover. You have nothing to lose at this point. If it is a defective head issue then you cannot rely solely on visual inspection - but you may get lucky. Don't forget to pick up a new Fel-Pro valve cover gasket...

 

I have another interesting thing to add, Sunday I used a can of throttle body cleaner on it while it was running, to clean it and maybe clean up some internal carbon. Ever since then my jeep will still flash the engine code at the same time as before but doesn't miss or sputter or anything else???????

Didn't have a chance to use my buddies high tech scanner yet but should be able to tomorrow.

No o2 sensors yet but did grad a MAP sensor while at a junk yard today

 

So i replaced my o2s ( both upsteam ) and still have the issue... Me and a few friends where pondering an idea, i had and fixed the normal heat soak issue on #3 and also wrapped # 4 just cause, but has anyone ever heard of a heat soak issue in the fuel rail? After thinking this I drove my jeep for alittle bit in the 93 degree heat then let it sit for a few minutes then opened the hood and used an infrared thermometer on the fuel rail, i got temps from 180 up to 210 on it. Any thoughts?

 

pulled the valve cover off today, everything was good, looked brand new in there.

 

When it sets a code, the PCM stores freeze frame data which is readable with any decent OBD2 scanner. You can look at fuel trim, IAT temp, coolant temp, TPS position, timing, load%, etc in the stored data to help figure out whats happening. The misfire monitor is based off the crank sensor and variation in speed so mechanical issues can trigger it.

The PCM will command a solenoid to purge the charcoal canister of absorbed fuel at start up, which probably is related to your misfire. The canister is part of the evap system.

 

You are 100% percent right, the other day I replaced a steel line from the canister to the tank, which fixed my evap problem but didnt help my misfire problem. I have borrowed scanners and looked at the freeze frame and live data but to be honest It doesnt really help if you dont know what your looking at. things like the IAT was good, timing, load, coolant, all seamed good, one odd thing was that the TPS shows 18% when the car is idle and 76% at WOT. One would think at idle the butterfly is closed and it should read 0% but I dont think this is my problem only odd looking data. The scanner also showed open/closed loop and that the PCM prevents the system from going to closed loop because it sees the misfire and after I restart the engine it goes to closed loop...... My thought on that is that the engine is getting pre set air/fuel info from the computer in open loop and something is throwing it off then when I restart it and it is in closed loop the sensors are compensating for the thing that is causeing my misfire......... million dollar question is what is causeing my open loop miss?

 

I feel your pain. I bought a '98 about three weeks ago, and have been doing battle with a P0301 since I got it home. I knew it idled a bit rough, but figured it just needed a tune up, injector cleaning, etc., so I bought it anyway. After I got home and dug into it, I saw that plugs, wires, cap, rotor, etc were pretty new, so I think the previous owner had been fighting it.

After swapping all the parts that I could between cylinders, nothing. I would clear the code, swap a part with another cyl, and start it up. Within a few minutes, the P0301 would be back as a pending code. Compression looked good. Found no vacuum leaks. Finally I stumbled upon a TSB for '96-'98 4.0s with a misfire. If no other cause could be found, it said to use Mopar Combustion Chamber Cleaner and replace the valve springs. I first used the cleaner. The code took about an hour to come back. Improvement! Next I swapped the valve springs on cyl 1. After nearly a week, she's still running pretty smooth.

I know this TSB doesn't apply to your Jeep. I wish I had an answer for you. Have you sprayed carb cleaner around the intake for cyl 4 to check for vacuum leaks? I don't really think that's your problem, but it's something to check. It just seems like a flaky sensor wouldn't affect only one cyl.

Best wishes to you...I know how frustrating it is! Keep us posted.

 

Thanks for the wishes, I need all the help I can get.... I tried the carb cleaner around the intake and so on and didnt have any luck. Ran seafoam twicw through it, and took the valve cover off to check the springs but didnt think about changing the #4 springs. Did you replace them with new ones or just swap cylinders? Also just to put it out there my jee has 144k on it but have found out that in 2005 it got a jasper engine put in it so there could be alot less miles on it.

 

I replaced the springs on cyl 1 with new ones from the dealer. The TSB said to replace all 12 springs, but this is a 181k miles vehicle that will see limited use, so I just tackled the problem cyl for now.

If your engine is a reman, is it possible it was originally in a '96-'98 that would be affected by this TSB? Hmmm...