Hello Everyone, I am currently experiencing a misfire issue on my TJ. I have read through the other similar threads here to begin diagnosing and fixing the issue, but with no luck so far. So I have decided to outline my issue as best I can below.
Jeep Information:
The Issue:
To preface; in the past, I had an intermittent P0300 Code (Random Multiple Misfire) that presented itself mostly in hot conditions. I was able to find that (I think) the issue was largely related to heat soak. This is why I purchased and installed the Fuel Rail & Injector Heat Shield Cover Kit outlined above. I now have not seen this specific code in a long while.
My current issue is that after a recent offroading trip on the way home the Jeep started to miss very bad below ~2,500RPM. Once I got above ~2,500RPM the issue is entirely non-existent. The Jeep will pop/sputter/lurch while the misfire is happening. Occasionally I will get a P0302 Code (Cylinder 2 Misfire) flash on the dashboard as well, however it will never stay logged in the system and goes away quickly. This led me to believe I have an issue with Cylinder 2.
What Have I Done So Far:
Trying to make this as easy to digest as possible...
GREEN = Something that is working properly / non - issue / good.
RED = Something I still have questions about / not functioning properly / may be an issue / bad.
Jeep Information:
- 2006 Jeep Wrangler TJ Sport / 4.0L I6 Engine / 6 Speed Manual Transmission
- 179,397 Miles
- Legacy Oil (all changes except for most recent): Mobil 1 High Mileage 10w30
- Current Oil (See Below): Shell Rotella T6 15W-40
- Spark Plugs Replaced at 168,960 Miles (Iridium Tipped, Unsure Brand)
- Fuel Rail & Injector Heat Shield Cover Kit Installed at 172,501 Miles.
- Has slight lifter tick in cold (winter) temps, but has not been heard in a while.
The Issue:
To preface; in the past, I had an intermittent P0300 Code (Random Multiple Misfire) that presented itself mostly in hot conditions. I was able to find that (I think) the issue was largely related to heat soak. This is why I purchased and installed the Fuel Rail & Injector Heat Shield Cover Kit outlined above. I now have not seen this specific code in a long while.
My current issue is that after a recent offroading trip on the way home the Jeep started to miss very bad below ~2,500RPM. Once I got above ~2,500RPM the issue is entirely non-existent. The Jeep will pop/sputter/lurch while the misfire is happening. Occasionally I will get a P0302 Code (Cylinder 2 Misfire) flash on the dashboard as well, however it will never stay logged in the system and goes away quickly. This led me to believe I have an issue with Cylinder 2.
What Have I Done So Far:
Trying to make this as easy to digest as possible...
GREEN = Something that is working properly / non - issue / good.
RED = Something I still have questions about / not functioning properly / may be an issue / bad.
- Removed / cleaned / Throttle Body, IAC, MAP, TPS, sensors and housings.
- They were all already relatively clean, but I still disassembled and further cleaned them.
- Tested for a vacuum leak by spraying the vacuum lines and intake area with brake clean.
- No drop in power at any time. Indicating no vacuum leaks.
- Removed, cleaned, and re-gapped spark plugs.
- Installed them into different holes to trace misfire, misfire cylinder did not change.
- Checked the inside of the spark plug holes with an endoscope
- Inspected pistons and cylinders. Nothing seemed too off, although it seemed some pistons were more suit covered than others. The cylinders looked good with visible clean cross hatching. Overall it was hard to see much with the endoscope.
- Compression tested all cylinders.
- On first attempt all cylinders read somewhat evenly. On the second attempt cylinder 1 was only reading 30-60psi. This is where I changed my focus to cylinder 1, away from cylinder 2.
- Wet Tested Cylinder 1
- Wet tested cylinder 1 and the pressure immediately came back to 180. Indicates worn/bad rings on cylinder 1.
- Seafoam Deep Clean and Oil Change.
- Sprayed Seafoam Spray into all cylinders, rotated the crank, and left overnight to soak. Ejected leftover seafoam, reinstalled plugs. Added seafoam to oil fill cap and ran for 15 minutes at idle. Finally immediately changed the oil and replaced with a Wix XP filter and Shell Rotella T6 15W-40. My hope in switching to T6 15W-40 was to have the extra detergent further clean the engine and also have the thicker oil create more of a seal around the piston rings.
- Removed exhaust and checked for clogged cats.
- One upper cat was entirely missing and hollow, the other appeared fine. Found a good amount of cat material in the exhaust and removed. Did not seem like enough to cause issues. Not looking to replace the exhaust right now unless you think this is my issue.
- Smoke machine tested the exhaust for leaks.
- No leaks were present besides extremely slight where the muffler meets the main exhaust and where the tip meets the muffler.
- Smoke Machine tested vacuum lines.
- No leaks except for EXTREMELY slight by the throttle body. Seriously do not think this is my issue.
- Better Compression Testing
- I want to run a compression test again possibly to get more accurate results on all cylinders and see if the Cylinder 1 issue was user error or real.
- Leak Down Test
- Need to purchase equipment, looking for advice on if this is worth purchasing / if so what brand is good?
- Coil Rail Replacement
- Coil Rail seems fine, its clean, not cracked, and not deformed in any way.
- Replace Crank/Cam Position Sensors
- No related codes so I dont think this will help.
- Replace Injectors
- This can get expensive, so I am not sure I want to dive on this yet before getting feedback here.
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