Persistent P0303 on my 2005 TJ — Coil Rail Replaced, Misfire Came Back. What Else Should I Check?

[TheManWithNoName]

Hey everyone,


Looking for some advice because this has been driving me crazy.


I’ve got a 2005 Jeep Wrangler TJ (4.0 / manual) that keeps throwing a P0303 (cylinder 3 misfire).

Symptoms​

• Misfire only happens after driving it for a while
• The car is running rough tho. From time to time, I can feel the car shaking at idle and then it goes back to normal
• No other codes besides P0303

What I’ve already replaced​

• PCM (a few months ago)
• Spark plugs (a few months ago)
• Coil rail (just replaced — Jeep idles smoother but P0303 came back)

My question​

Since the misfire is ONLY on cylinder 3 and only shows up when the engine is hot, where should I look next?
Could it be:

Thank you,

 

[lBasket]

italian tune-up

 

[macleanflood]

Compression and leak down test.

Pull the valve cover and see what the rockers and pushrods are doing.

-Mac

 

[GoldenGorilla]

You also didn't mention removing and inspecting the spark plug on Cyl 3. Could also be a cracked o-ring on the injector for cylinder 3 causing it to go lean. Do you have O2 sensor differences between B1 and B2?

 

[Link]

It’s a heat soak issue on the fuel injector. Had the same issue on my 2005. Well known issue. Easy to fix.

I also bought a DEI shield and fuel rail wrap from Amazon to try to keep the fuel a little cooler till it hits the injector. The DEI shield kit on Amazon says it doesn’t fit the 2005….but it does.

https://wranglertjforum.com/threads/cylinder-3-misfire-and-p0303-code.10363/

https://www.amazon.com/dp/B015NOKWQY?tag=wranglerorg-20

 

[ItchyDong]

Before guessing anymore, swap injectors with a known good cylinder. If the misfire moves, you know it’s a bad injector. If it stays on 3, verify power and control (ground) at the injector plug with a 5 second noid light test. If it’s good, then wrap your injector.

I say this because most of the time it’s heat soak, there’s a P300 associated with the P303, and its usually an issue after shutting it off and cranking it shortly after it’s shut off. Not after “driving it for a while”.

 

[Link]

https://www.amazon.com/gp/aw/d/B007O3QHDK?tag=wranglerorg-20

 

[AOSJ]

https://www.amazon.com/gp/aw/d/B007O3QHDK?tag=wranglerorg-20

what do you do with these?

 

[bucky]

I had the same issue with my 05 last yr after replacing the injectors, heat shields and new plugs. Turned out to be a bad new spark plug. In all my years of replacing plugs I’ve never had an issue with a brand new spark plug. No issues aince.

 

[Link]

what do you do with these?

Cut them and wrap the number 3 fuel injector with them. Factory fix established by Jeep

Link is in the post above but here it is again.

https://wranglertjforum.com/threads/cylinder-3-misfire-and-p0303-code.10363/page-2

 

[AndyG]

I agree, sounds totally like heat soak in the Florida sun. I’m in Alabama and fight it too.

I have a friend who contends since they didn’t do it new, that the fuel system loses its ability to hold pressure under intense heat over time, via a weak check valve spring.

Sounds plausible but not proven and guys who have replaced pumps said it did not go away.

 

[bucky]

I replaced what was left of the OEM heat shielding with a kit from DEI. I bought this,4 hole injectors and new wire pigtails fro K Suspension. I regularly run in the desert heat and never had an issue.