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Stubborn Misfire on 5

NewJeeper2020

NAXJA Forum User
Location
Michigan
I think I originally posted this in the wrong area, so let's try this!

Hey everybody!!

This is my first post here, and the first time I've posted anywhere about my Jeep! I am usually able to find a solution to the problem I'm facing, but this one is a bit of a doozy. I am by no means mechanically inclined and have been self-taught through several forums and Youtube, so if the answer is painfully obvious please tell me! This post may be a bit long, but I want to give you all the details I can. I have a 2001 Jeep Cherokee Classic, 4.0L, 180k miles, 160A upgraded alternator, Big 3 upgrade from JeepCables.com, new 4-hole injectors from a reputable source on eBay that I found through, and all other changes have been more cosmetic, new bracket for the center console, stuff like that. ANYWAY!

So the situation:

The jeep starts up just fine. It has a little bit of a rough idle whenever I come to a stoplight but nothing concerning where it's hesitating when I step on the gas again. Driving down the road is the same story; it handles beautifully, and it doesn't feel like anything is wrong. Once it gets up to operating temp and I come to an extended stop and put it in park, say like in the garage, and I'm talking on the phone with someone, I get the same rough idle I do at stoplights, but now I'm in park. Then after maybe 5-10 mins of idling and the tach is just barely bouncing directly under the second small hashmark, and without feeling anything buck or jump, the CEL comes on, and it reads as a cylinder 5 misfire (P0305).

Things I've done to address it:
- New plugs (NGK), properly gapped at .035
- New coil pack
- Ran seafoam through the intake
- Added a heat shield between the injectors and the intake, as well as heat wrap on the fuel rail, the injector wiring, and the injectors themselves (probably overkill but *shrug*)
- Ran a full bottle of Seafoam through the gas tank with a full tank of gas
- I just had the head replaced with a clearwater head which I've read positive reviews on both here and other forums
- Head also came with new rockers, springs, and valves
- The new head came with new exhaust, head, and intake gaskets
- New high output alternator (not done to fix the problem but I want to be thorough)
- Just swapped the injectors 456, with 123 to see if the misfire would follow but it stayed on 5

Next steps:

I am a bit at a loss and I am running out of money to throw at this thing, especially with a pandemic on our hands obviously food comes before the jeep (at least for me it does!!), but with that being said I think the following steps will be to replace the CPS (from what I've heard online), look into replacing the O2 sensors, and possibly replace the cat? But if I can avoid firing the parts cannon at this thing that's the route I'd like to take.

Thank you for taking the time to read!
 
Switch the #5 injector to a different cylinder to see if the misfire moves.
Rebuilt, Ebay injectors are a crap shoot, you never know how well they were cleaned and flow matched.
 
I would start by carefully inspecting the harness for insulation integrity, that's where it started with my 2000.
 
Thank you all for the responses! I did swap injectors and the misfire stayed on #5. I will check out the harness and see if I find any breaks, do you know of any spot where it usually rubs through overtime or specific areas I should focus on?
 
It won't be a break but a short to other wires, that really requires a megger check. The common area it seams is above the #5 and #6 intake/exhaust manifolds.
 
I had the same issue on my 96. Always #5. New upstream 02 sensor fixed it after trying everything else (injectors, plugs, wires cap, rotor, cam sensor, CPS, etc).

Good luck
 
hello everyone!

Things have been a little crazy around the house, but I finally got around to the plugs. Swapped the 5th and the 2nd plug, both looked exactly the same, not too warn down, not wet or anything like that and the gaps were still good. Ran that for a few days and when I pulled into the driveway and finished a phone conversation yesterday BAM the misfire popped back up and sure enough still on the 5th cylinder. I haven't had the chance to look for blowby yet so I'll do that in the next day or so since it's an easy test. I will also look into buying some new upstream O2 sensors to see if that helps (thank you for the top Jesse!) Also checked all the wiring and couldn't find a break. I'm really hoping that this isn't a piston ring. The whole debacle with the head was already expensive and I'd love to avoid another major expense if I could. Also found out the blower motor resistor is melting so I just ordered a new one of those too lol That is an easy enough fix, now if only the misfire was something just as easy. Besides the blowby/piston ring issue, does anyone have any additional things I could test for?

Note: I also noticed that if I'm sitting in park the idle is just below the second small hashmark and if I rev the engine a bit and then let off the gas (fluttering a bit) the engine will bog down, and the RPMs almost drop to zero, the lights dim, it struggles, and almost stall out, could this be something related to the misfire or is this something completely different? Hoping to get this thing in better shape so I can move during the summer and any help would be greatly appreciated!

Thank you all!
 
Okay!!

So I checked for blow-by in the crankcase and no bubble and no smoke or steam or anything out of the engine when it is at operating temp and I have the cap off so I'm open if anyone has some next steps. Based on what I've seen online, and to avoid replacing all 4 of my O2 sensors I ordered a cam sensor and a CPS from NTK and will be replacing those soon as well.

I was curious if anyone, maybe Messy Jesse, has some advice on how to go about changing the CPS. That thing seems so inaccessible it is unbelievable, I assume it'll just take a lot of patience and about 5 feet in extensions but any words of wisdom would help!

And I picked up a camshaft sensor as well, just the little grey piece with two screws. I am a total novice so I'm curious is replacing the cam sensor as easy as popping off the two screws and throwing the new one on? or do I need to make any adjustments for timing?

Thank you!
 
Does anyone have any guidance on how to change the plastic part of the camshaft sensor? Can I just unscrew it and then toss the new one on or does the engine need to be in a specific spot for me not to mess anything up?

Thank you!
 
It's indexed to where you can only put it on one way.
 
any codes? I'd get a code reader on it ASAP
 
Okay!!
I was curious if anyone, maybe Messy Jesse, has some advice on how to go about changing the CPS. That thing seems so inaccessible it is unbelievable, I assume it'll just take a lot of patience and about 5 feet in extensions but any words of wisdom would help!

While it will not help you now, when the head or the entire engine is removed, rearrange the wiring harnesses going down the driver's side past the transmission and tie them back with zip-ties.
I did this when the engine was out in my 2001 and now the CPS is easily visible. Yes, it takes about every extension you carry to get to it, make sure you always have enough of them in your toolbag.
And don't drop the bolts into the bell housing!
 
Hey everyone!!,

I know it has been quite a while but I thought I'd keep everyone updated just for consistency's sake. I ended up replacing the Camshaft sensor, never got around to replacing the crank since the ol' girl fired right up and was running like a top with the new cam sensor.

Fast forward to today: I made the long drive from Michigan to Washington DC and have been using it just for trips to the store and whatnot and just yesterday it threw 4 codes at me. Was running a little odd in traffic: bouncing RPMS (from 800-1000) and didn't buck or anything but threw the codes (P0300, P0305, P0306, and a new one P1294) I just replaced the IAC in January with a Mopar part, so I don't think it is that. Could my misfire just be caused by a vacuum leak hidden somewhere? There is a shop in Northern VA that has great reviews online but wants to charge me $139 an hour to run diagnostics on it. As I think I said before, I'm not the MOST mechanically inclined person but I do like working on this thing myself, however without a garage I am kind of at the mercy of whatever the shop is going to charge. Is 139 a lot? Should I try finding somewhere else? What else could cause all these codes to pop up like this?

Thank you for reading!!
 
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