Post ODBA replacement cylinder 1 misfire (reoccurring every 150 miles)

[Tycod TJ]

Hey all,

I’ve got an ’05 TJ 4.0, and recently it threw a Camshaft Position Sensor code. From past experience, I didn’t want to risk it, so I took it to the shop to have the sensor and ODBA replaced. (Last time I let it go too long, planning to replace it myself, and the ODBA shaft shattered, spitting metal into the motor—ended up needing a full replacement.)

This is my second engine—a used motor with around 150k miles. Since it’s my daily driver, I figured it was better to handle it sooner rather than later on this one as I know the OEM ODBA seals fail at around 150K.

Here’s the issue: after getting it back, I’m getting a flashing CEL for a misfire on cylinder 1. I can feel the rough idle or stumble right before the code pops up. The misfire is consistent and always on cylinder 1. After restarting the engine a few times it goes away, but will come back in the coming days, usually.

I’m not a mechanic, but I’ve turned a few wrenches and worked in a basic repair/inspection shop way back in the day. That said, I’m not sure what could be causing this after replacing the sensor and ODBA.

Anyone have thoughts on what to check next or common issues that could cause a misfire post-ODBA replacement? Appreciate any advice.

 

[macleanflood]

Compression test?

-Mac

 

[Tycod TJ]

Yep, compression tested, checked the plugs, swapped plug cylinders, same code.

It just threw it again, I am in the process of checking all the sensor wires, going to check the fuel pressure, might go ahead and change the coil pack also, I replaced it sometime back with an aftermarket, maybe it was too cheap...

I also noticed that part of the heat shield around the first two injectors is totally gone, so I'm wondering possible vapor lock, although I know that is usually a cyl 3 thing on these 4.0Ls. Regardless, ordering some shielding now.

I just don't know enough to know if the new OBDA and cam shaft pos sensor could be causing it to read a misfire, as it was not misfiring prior to replacing them.

I also think I'm having an issue with oil sludge, had my oil pressure needle completely drop a few time over the last couple days, changed the oil and found evidence of some sludge. Could all this be heat related?

 

[Juggernaut]

What brand did the shop replace the OPDA and crank sensor with? Also do you have access to a scanner that will show the learned difference between cam/crank?

 

[Tycod TJ]

What brand did the shop replace the OPDA and crank sensor with? Also do you have access to a scanner that will show the learned difference between cam/crank?

I'm not sure the brand... But I'm guessing it wasn't the CROWN one. Honestly, I like the shop, I take my wife's exploder there, they are trusted in the community... but I never got the paperwork on this repair at all. Going to head back over there and get it and see if I can't figure out which odba they put in. My guess is an OEM one though. You think it could be a faulty part/sensor?

I do have a reader that will give me live data charts of the sensor timings.... although I do not really know what to look for... Time to dive into another learning hole

 

[AndyG]

A friend of mine recently learned that sometimes a very, very slight adjustment of the unit makes the difference in success and failure.

 

[Juggernaut]

A friend of mine recently learned that sometimes a very, very slight adjustment of the unit makes the difference in success and

Exactly. Bringing the difference to as close to zero or performing a crank relearn is where I’d start.

 

[sab]

What brand did the shop replace the OPDA and crank sensor with?

I'm not sure the brand...My guess is an OEM one though.

Doubtful - the Mopar OPDA has been discontinued for years.

Anytime the OPDA is changed, the Relearn procedure is good to do. Also, if the sensor was replaced (especially with an aftermarket sensor), you'll have best luck by manually adjusting the position of the OPDA to get the Cam/Crank Difference as close to zero as possible before performing the Relearn procedure. The aftermarket sensors don't seem to be as precise as the OEM sensors (which are very hard to find), so manually adjusting the OPDA can prevent DTCs related to cam/crank sync issues, like your P0301 misfire code. More detailed info here.

And welcome to the best forum on the Internet!