1998 Jeep Wrangler Sport (4.0L) Error Code P0301 (Please Help)

[montego1]

My Jeep has been a great runner, but the Check Engine Light(CEL) is on with 1xP0301. The reason I said 1x, is that it only gets one code after a clear it. I will drive it for weeks and no additional codes show up, and only the one P0301 has been thrown.

Jeep is running fine, not rough or cutting out or anything. I have noticed that when it starts, it kicks a bit.

1998 Jeep Wrangler Sport (4.0L) Error Code P0301 (Please Help)

Things I've done:

1) New spark plugs (several times)
2) New Distributor cap and rotor
3) Replaced all 6 fuel injectors
4) Replaced the coil
5) New plug wires
6) New throttle body position sensor
7) I found I had a crack in my exhaust manifold during all this, so i replaced it with a nice performance one. I also replaced the gaskets.
- Jeep sounds great and even runs better
8) New Battery (Gold Die Hard)
9) Air filter, oil change & filter
10) New performance radiator a couple years ago.

The next thing i'm going to do is check the compression on all cylinders.

I can't get it registered with the CEL on. Please help!

 

[expomazda]

You have covered the basics and then some! I would check the wiring going to the fuel injector. Might possibly have an intermittent short. If you have access to a labscope, I would watch both the power and control side of the injector and start wiggling wires and watch for it to drop out.

Sent from my XT1585 using Tapatalk

 

[Mitch502]

Compression or wiring sounds like the only thing left. I HIGHLY doubt it, but you might try checking your fuel pressure. If it's low, I think cylinder 1 is the front most...so maybe there isn't enough pressure to get a good injector spray...again, not sure how plausible this is.

Does it do it all the time, or only when it gets warm/hot?

 

[bellevue260]

I did a search with the code and for one guy it was a bad flywheel.
http://www.cherokeeforum.com/f2/cylinder-1-misfire-code-p0301-43255/

 

[Mitch502]

Hmmm, that sounds like the 1/10,000 chance, lol. But I guess It can't hurt to check. You should have the inspection plate you can take off and look.

 

[montego1]

I'm going to inspect the wiring to the fuel injector and check the fuel pressure this weekend. I also will check the compression on all cyl. When I reset the CEL, it will come back on just driving down the street, it looks like it is always at temp when it comes on. I have a 4Runner that had misfires with several cylinders (P030X) and it did show several misfires on certain cylinders, each time after a reset. A bad coil and a bad wire corrected all of them. I also had a bad fuel injector several months after replacing the wires.

The point is, with this jeep, only one misfire (P0301) occurrence happens after I reset it. I can drive it 100's of miles and when i check the status, it is only one misfire. I have troubleshot P030X errors on several vehicles, (4runner, Honda, Jeep, and several Toyotas) and have always corrected them. I may have to scrap the Jeep if i can't register it. It's in good shape, new tires, brakes, everything I listed above new. I would hate to scrap it just for this error.

------------------------------------------------------------------------------------------------------------------------------------------------------------
Below is what my Auto Computer (CP9580A AutoScanner Plus) spit out as the TOP Reported fixes. I guess I could start working down this list...

DTCs (Codes) P0301 MOD $D1 Cylinder 1 Misfire Detected = CONFIRMED
==================
TOP REPORTED FIX
1-Cleaned Fuel System

FREQ REPORTED FIXES
1-Cleaned Engine Carbon
2-Cleaned Engine Valve(s)
3-Repaired Engine Valve(s)
4-Replaced Spark Plug(s)
5-Replaced Cylinder Head(s)
6-Replaced Engine Valve Spring(s)
7-Repaired Fuel Injector Wiring

ALSO REPORTED FIXES
1-Repaired Crankshaft Position (CKP) Sensor Wiring
2-Repaired Cylinder Head(s)
3-Decarboned Engine
4-Performed Engine Carbon Cleaning Procedure
5-Performed Engine Tune Up
6-Decarboned Engine Valve(s)
7-Replaced Fuel Pump
8-Replaced Ignition Coil Rail
9-Replaced Ignition Coil(s)
10-Cleaned Intake Manifold
11-Replaced Powertrain Control Module (PCM)
12-Replaced Spark Plug Wire(s)
13-Cleaned Throttle Body
14-Replaced Throttle Position Sensor(TPS)
15-Replaced Valve Stem Seals

5/1/2016
====================
Update: Jeep Compression tests

Cylinder: warm
1) 130
2) 145
3) 145
4) 140
5) 145
6) 140

Cylinder 1 is a little low.

=======================
Fuel Rail PSI: 50-55 Warm

I did the FUEL Injector test: unplugged the #1 cyl while the engine was running and the engine did not even change and start running rough. I may have a bad
injector.

 

[montego1]

Update:

I unplugged the fuel injector wire on the number 1 cyl, and measures the resistance across the two contacts of the injector coil. It measured 12.1 Ohms. All the other ones measure about 12.5 ohms or so. I removed and replaced that injector (Cyl #1) with a new one. Resistance is around 12.5 on the new one. The engine light did not come on for a day or so, but it did come back on.

Still have the P0301 with CEL ON.
===============================================================================================
I may pull the head and replace it.

More updates later...

 

[montego1]

Hey, Thanks for the reply.

I checked the fuel pressure and it's around 55-60 psi. The fuel line is closest to cylinder #1, #6 is farthest away. I replaced the #1 fuel injector after doing some more tests. Still have the P0301 Error.

5/1/2016
====================
Update: Jeep Compression tests

Cylinder: warm
1) 130
2) 145
3) 145
4) 140
5) 145
6) 140

Cylinder 1 is a little low.

=======================
Fuel Rail PSI: 50-55 Warm

I did the FUEL Injector test: unplugged the #1 cyl while the engine was running and the engine did not even change and start running rough. I may have a bad injector.

 

[Mitch502]

Hmm, you can get some better injectors for it, which might actually help with emissions. They're "784's" out of the 2.4L Chrysler stuff...You can also use the (color) neon orange injectors out of Fords that are "917's"


I have a set of 917's I can sell you if you want to go that route. Do some research...

FWIW, I had a SLOOOOOW starting problem with my Jeep. It was a 10-15 second crank time, unless I primed the key multiple times...I thought it was the fuel pump, that wasn't it....thought it was the check valve on the pump...that wasn't it...put a set of injectors in it and now it starts in under 2 seconds.