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Discussion Starter #1
I just bought a '98 Cherokee 4.0, and I'm regretting it. Engine ran a bit rough at idle when I looked at it, but figured it just needed a little TLC. Well, it has a P0301 (cyl 1 misfire) that I can't figure out. This is my first real experience with a 4.0, so I'm hoping you guys with more experience can help me out.

I have:

swapped plugs w/ cyl 2 (cyl 1 plug did look a little darker, but wasn't wet)
swapped plug wires w/ cyl 6
swapped fuel injectors w/ cyl 2
swapped fuel injector connectors w/ cyl 2
inspected cap and rotor (they look new)
checked compression in cyl 1 (130 psi)

Between each of the "swaps", I cleared the code. Then I started it, and after a few minutes of idling, P0301 would show up as a pending code.

It has 181k miles on it. Any help is much appreciated!
 

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Discussion Starter #2
Just a quick semi-update. A co-worker had sent me a link to the public library's auto repair section, where I can read TSBs. There is a TSB about misfires, and the fix is to use Mopar Combustion Chamber Cleaner and replace the valve springs (apparently with a revised part). Hopefully the local dealer has some cleaner on hand, and I'll try it this weekend.
 

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TSB # 09-003-03 doesn't really apply to your Cherokee. It covered '99-'04 4.0L engines that ran at lower rpm duty. The heavier exhaust valve springs helped to overcome tight valve guides and prevent valves from hanging up. Chrysler tightened up clearances to quieten up the 4.0L in 1999.
It gives the part# for the Mopar Combustion Chamber Cleaner. Reading the procedure may help your diagnosis, but may not offer a fix. A valve leakdown test for cyl #1 may tell you more.
http://www.wjjeeps.com/tsb/tsb_wj_0900303.pdf
 

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Discussion Starter #4
Thanks for your reply, IC. The TSB I found was 18-31-97. It says it applies to 96-98 Cherokee and Grand Cherokee, and 97-98 Wrangler, all with the 4.0. It says to use the cleaner, and replace all 12 springs with part number 53010388.
 

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You are correct. I skipped over that one because I didn't think that the TSB title: 'OBD II misfire monitor' applied to your problem.
18-31-97 superseded to 18-22-98.


[background=transparent]NO: 18-22-98[/background]
[background=transparent]GROUP: Vehicle Performance[/background]
[background=transparent]DATE: Jun. 12, 1998[/background]
[background=transparent]SUBJECT:[/background]
[background=transparent] Misfire Monitor[/background]
[background=transparent]THIS BULLETIN SUPERSEDES TECHNICAL SERVICE BULLETIN 18-31-97, WITH EFFECTIVE DATE OF JAN. 30, 1998 WHICH SHOULD BE REMOVED FROM YOUR FILES AND NOTED IN THE 1997 TECHNICAL SERVICE BULLETIN MANUAL (PUBLICATION NO. 81-699-98004). THE DECARBONIZING PROCEDURE HAS BEEN REVISED ALONG WITH THE LABOR OPERATION TIME ALLOWANCE. ALL REVISIONS ARE HIGHLIGHTED WITH **ASTERISKS**.[/background]
[background=transparent]MODELS:[/background]
1997 - 1998 (TJ) Wrangler
1996 - 1998 (XJ) Cherokee
1996 - 1998 (ZJ) Grand Cherokee

NOTE :THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH THE 4.0L ENGINE.

[background=transparent]SYMPTOM/CONDITION:[/background]
[background=transparent]Malfunction Indicator Lamp (MIL) illuminated with either a Multiple Misfire or individual Cylinder (1-6) Misfire Diagnostic Trouble Code (DTC) recorded in the Powenrain Control Module's (PCM) memory. The MIL illumination may be accompanied by engine vibration.[/background]
[background=transparent]DIAGNOSIS:[/background]
[background=transparent]Refer to the 1998 2.5L/4.0L/5.2L/5.9L SF1 Jeep[/background]
[background=transparent] Diagnostic Procedures Manual (Publication No. 81-699-97019), test TC-106A for the Multiple Cylinder Misfire DTC or test TC-107A for the Cylinder # (1-6) Misfire DTC. For any future reference, record and document Freeze Frame data.[/background]
NOTE :BOTH TEST TC-106A AND TC-107A ARE REVISED WITH TECHNICAL SERVICE BULLETIN 26-12-97 RELEASED DECEMBER 1997. DO NOT USE THE PROCEDURE LISTED IN THE DIAGNOSTIC PROCEDURE MANUAL UNLESS THE REVISED PAGES HAVE BEEN INSERTED.

[background=transparent]Perform the repair procedure identified in the Powertrain Diagnostic Procedures Manual unless your diagnosis identifies that an engine mechanical problem could be causing the OBD II Misfire DTC. If the Powertrain Diagnostic Procedures Manual identifies a possible engine mechanical problem, perform the Repair Procedure.[/background]
[background=transparent]Here is the repair procedure.[/background]
[background=transparent]1. Operate the vehicle until the vehicle reaches operating temperature.

2. Remove the air tube from the throttle body.

3. With the engine at an idle, spray the entire contents of Mopar Combustion Cleaner, p/n 04318001, directly into the throttle body. Allow the vehicle to load up with the cleaner to the point of almost stalling out.

4. Shut the engine OFF after the entire can is ingested.

5. With the hood closed and the vehicle parked inside the garage, allow the vehicle to soak for two to three hours. This will ensure that the engine will maintain its temperature and will allow proper solvent penetration.

6. **Drive the vehicle to fully warm up the engine.

7. If the vehicle is equipped with an automatic, place the gear selector into L, if the vehicle is equipped with a manual, place the transmission into first gear.

8. On a suitable road that will allow the vehicle to be driven safely at the posted speed limit, accelerate the vehicle until the engine reaches 4500 rpm.

9. Hold the engine speed at this rpm for 15 seconds.

10. Slow down and pull to the side of the road, then allow the engine to idle for five seconds.

11. Repeat Steps 7 through 10 two more times.**

12. With the vehicle at operating temperature and within the freeze frame data recorded for the diagnostic test, verify that the misfire condition has been corrected. [/background]




[background=transparent][background=transparent][background=transparent] [/background][/background][/background]
 

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Discussion Starter #6
Thank you very much for the updated procedure. I picked up a can of the cleaner at the dealer. I hope to get a chance to do it this weekend.
 

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Discussion Starter #7
I completed the procedure on Sunday. When I got home, I thought it was running smoother. I cleared the code, but only had time for a short test drive. No code during short drive (5-10 min).

Today I started it and let it run while I added some 134 to the AC. After that, I loaded up the family and we went for about a 30-40 min drive. I did some slow driving around town, some highway driving, and a couple of short full throttle runs. No codes. I began to feel some relief!

Later tonight, I drove it around the block to park it behind the garage. I still had the code reader in it, so for the heck of it, I looked for pending codes...it's back! I cleared the code, started it and let it idle for a few minutes, and P0301 was again a pending code. Right back where I started! Grrrr!!

So, any thoughts about this, IC? Considering the results I got, would another treatment of cleaner be a good idea? Thanks for your help!
 

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Discussion Starter #8
I'm also wondering about the other half of the bulletin, replacing the valve springs. What do you think?
 

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I have a 1996 Cherokee I have replace the crankshaft sensor, fuel pump, fuel filter, pickup coil, coil. I keep losing power and fuel pressure. It is not giving me any codes. I can be driving down the road and out of no where it just dies will restart most of the time how ever there is times it will not restart. We have check the pcm by unplugging sensor and we gives those codes. I am ready to drive it right into a tree or the dealers @#$. PLEASE HELP.
 

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If you have to unplug the crank sensor in order to check the PCM, then it sounds like the sensor is defective (i.e.-shorted?).
Was this sensor replaced with an OEM-style part?
Are you sure that the wiring harness is OK? Make sure that the connectors are clean and secure.
A failing PCM is the last possibility.
The dealer has a Co-pilot tool that can record the events leading up to a stall. It can hold 3 separate 90-second data recordings.
They may waive a diagnostic fee if you ask and have been in previously for this concern. Back at the shop, the Co-pilot data recording can be analyzed to find out what happened.
 

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Discussion Starter #11
I apologize for failing to update this thread. New valve springs on cyl 1 cured the misfire. Unfortunately, in early October, it suddenly developed a knock, though it continued to run well. I finally dropped the oil pan, and found this:


Yep, pieces o' piston (#6). It's been sitting in my garage ever since. Still not sure what I'll do with it.
 

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Depending upon the condition of the Jeep, good condition XJ's can sell for up to $10,000 here. That would make it a candidate for either a rebuilt long block, or salvage yard engine. If you wanted to get it back in the road again.
 

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I had a 97 Grand Cherokee with a misfire code. It only set on hard acceleration. I was living with it until a jerk broadsided it and wrecked it.
 
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