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Discussion Starter #1 (Edited)
2005 TJ Rubicon auto has check engine light that comes on when driving at highway speeds. Not often but on long hauls during trips. Engine code is misfire usually cylinder 2 or 4. Engine runs well no misfire noticed.

Dealer replaced PCM, all O2 sensors, plugs, plug wires, new crown OPDA 2 years ago. The check eng light problem showed up on the first trip. Dealer gave me shrugged shoulders. I have the old OPDA and with original Mopar sensor.

I am going to install the original sensor and hope this cures the misfire codes.

I know this has been talked about here on ROF forever but I forgot until I found this utube video on the check eng light and the crankshaft sensor.

Question: The video has the crank shaft position sensor on the engine, older model! To be sure the 05/06 crank shaft sensor is on the OPDA?



Grand Staircase-Escalante Utah
 

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Cam sensor in the opda


The crankshaft position (CKP) sensor is mounted to the transmission bellhousing near the rear of the engine block.
The sensor may be mounted to the transmission with one of the following four different configurations:


  • with one bolt to the right side of the transmission if equipped with a 42RLE automatic transmission
  • with one bolt to the left side of the transmission If sensor is equipped with one mounting bolt, it is adjustable..
  • with two nuts to the left side of the transmission
  • with two bolts to the left side of the transmission
 

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Discussion Starter #4
The Crankshaft Position sensor 05 TJ Rubicon cost.

Jeep dealer Mopar part $63

OReily's Standard Brand $23

I have read use Mopar. Any opinions on that?
 

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Discussion Starter #7 (Edited)
Dang, went to the dealer to get the "right stuff" and they sold me the wrong sensor!

The 05/06 sensor does not have a wire pigtail. The sensor is separate and plugs into existing female fitting coming out of the wire bundle.

The one the dealer gave me was for an 02 wrangler I now see.

The one I got has a pigtail and female plug. Only way to make this work is to cut the wires and splice. No, I won't do that.

There goes my Christmas day quick Jeep repair:(
 

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Discussion Starter #8 (Edited)


Got the old sensor out. You can see metal filings have built up like you would see on a magnet. Maybe the reason for the erroneous misfire codes.

What do you think. Clean the sensor off and reinstall? Or go ahead and wait to get the new sensor from the dealer?

Note I cleaned it off and reinstalled. Now will need to test drive a few hours.



Show and tell ;)

Here is are the two sensors. On the left 05/06 Rubicon, on the right earlier wrangler 4.0.

 

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I'd clean it and run it.
 

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Discussion Starter #11
Checked the wires to and into the bundle, all look good.

Went for a long highway drive and ran the old sensor cleaned off and dang got the check engine light and misfirer code again.

Went down to the dealer and exchanged the wrong sensor they gave me and got the correct 05 sensor and reinstalled.

With brand new crank shaft sensor will take the Jeep out again on a highway run tomorrow.

Please scan your memory banks, I will be asking what to do next if this misfire code show itself again with the new sensor?

Two gals and a Jeep on a Utah shelf road north of Mexican Hat
 

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Did the coil pack get replaced? Grabbing at straws here - what about the injectors? Fuel pressure at the rail?
 

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Discussion Starter #13
Bad news: After replacing the crankshaft sensor with OEM, drove the Jeep about 1/2 tank on the highway and the check eng light flickered and code check showed again the dreaded PO304, #4 cylinder misfire. No solid light but I know it would do that eventually.

Note: The engine runs smooth and strong and when the misfire code comes up the engine does not react at all. I have now found what appears to be good directions for a fix, link below. What I will do now is check the coils and do a compression check and then go from there.

https://www.700r4transmissionhq.com/p0304-jeep-wrangler/
Excerpt:
P0304 Trouble Code Diagnosis- Jeep Wrangler - There are quite a few things that can cause the P0304 trouble code to trigger the Jeep Wrangler. Here are the most common problems that will throw the code. They are presented somewhat in order from most to least likely to be causing the code:

Bad Spark Plugs– replaced
Spark Plug Wires– replaced
Coil Packs–
Bad Fuel Injector–
Vacuum leak– smoke checked
Cam or Crank Sensors– both replaced
Low Compression–

Jeep club members tackling a black diamond section of the Defense Mine Paniment Valley near Death Valley California



J
 

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When you erase you trouble codes your scanner probably clears the pcm's memory. The pcm will relearn the adaptive numerator to monitor misfire. It relearns this under deceleration. That's why you have to drive it before it resets.
If you don't experience any other symptoms then I would start with compression and leak down test. If you don't have a leak down tester then buy a cheap one from amazon or whoever is cheapest. A cheap one might not be the most accurate but you can check all the cylinders for comparison. Lots of times compression will be good but a leaking valve will show up with a leak down test.
I would suggest swapping injectors from cyl 4 to 1or 5,6,2. But I worry that it might not come apart easily. You would probably be in for some new injector O-rings.
Something to think about is that the pcm detects a miss solely on how you flex plate rotates. It is looking for pulses in the way it speeds up and slows down. If you flex plate was damaged or you had a harmonic balancer out of balance then that would be perceived as a miss fire.
 

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Discussion Starter #15 (Edited)
When you erase you trouble codes your scanner probably clears the pcm's memory. The pcm will relearn the adaptive numerator to monitor misfire. It relearns this under deceleration. That's why you have to drive it before it resets.
If you don't experience any other symptoms then I would start with compression and leak down test. If you don't have a leak down tester then buy a cheap one from amazon or whoever is cheapest. A cheap one might not be the most accurate but you can check all the cylinders for comparison. Lots of times compression will be good but a leaking valve will show up with a leak down test.
I would suggest swapping injectors from cyl 4 to 1or 5,6,2. But I worry that it might not come apart easily. You would probably be in for some new injector O-rings.
Something to think about is that the pcm detects a miss solely on how you flex plate rotates. It is looking for pulses in the way it speeds up and slows down. If you flex plate was damaged or you had a harmonic balancer out of balance then that would be perceived as a miss fire.
Thank's rlenglish, appreciate your response, couple questions. The flex plate, is that the engine flywheel?

Edit: Ok got it. A 2005 Jeep flex plate is outrageously expensive if I remember correctly!

In case it means something...The check eng light comes on when reaching the top of a grade and the engine throttles back to keep constant speed.

I'll start with the leak down test, have done that years ago.
Then injectors.
Also look for something rotating out of balance on the engine.
 

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I'll start with the leak down test, have done that years ago.
The leak down test showed the source of the misfire codes on my '06. Leaking #6 exhaust valve.

After tear down, verification of leak down test with a different kind of leak down test :D.






And all better, ready to go back together.






Machine shop said they see a lot of sunken valve seats like that with late production ('05-'06) 4.0's. New hardened seats, should be good to go for the duration now though.

I drove it quite awhile with that burnt valve and associated misfire, long enough to ruin the pre-cats. Had to replace them almost immediately after getting the valve job complete. Now at over 116,000 miles the old pig is running the smoothest I can remember it ever running. MPG ain't improved a lick though :D.

- DAA
 

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Discussion Starter #18 (Edited)
OP update on P0304, #4 cylinder misfire code.

Today did a pressure check on cylinder #4 to check the valves, followed utube video instructions, hooked up 80 psi air from compressed air tank while engine cylinder was at TDC and listen for air passing through valves or rings. No air at all so valves and rings are tight so hopefully that eliminated having to do a valve job. Note this test then eliminates the need for a leak down test.

All NGK zfr5n spark plugs had extreme large gap and and looked worn. These plugs were put in by the dealer and only 10k miles on them. I will replace them and test drive and hope this was the source of the misfire code.

Searching forums for the best plug one stands out as a favorite, autolite APP985 double platinum. In second Champion 7034 double platinum and AC delco iridium. Which plugs do you recommend?

EDIT: I have read some older forum post that new plugs did indeed fix cylinder misfire codes. Hope this is it!


 

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Good find Bob. Recommendations I've read lean toward the factory NKG plugs. I think these were included with my RIPP supercharger kit.
 

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Those plugs are not good.
I have never had any luck using Autolite.
 
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