Help with flashing CEL and slightly rough idle

[rublicon]

2005 Wrangler Unlimited Sport 6 Speed Manual with 160ish thousand miles. Had for almost 3 years and about 30k miles. PCM has been replaced with Wranglerfix PCM about 2ish years ago.

Since September, I have been fighting misfire codes, initially a p0301 though at some point of throwing parts at it, I got a few p0304 and p0300. Currently I am no longer getting a misfire code, the only code I am getting is p0172 (system too rich bank 1) but I am still getting a flashing CEL, usually at idle or in stop and go traffic. I believe a flashing CEL implies misfires but it is not storing a misfire code anymore.

I have done the wrong thing by throwing parts at it to see what sticks and am currently at a loss and looking for direction on what to try next.

Here are the things I have done:
- Spark plugs - first did Autolite iridium fine wire something or another gapped at .040. Reading about spark plugs makes me want to shoot myself in the face by the way. To make sure that those plugs weren't part of the issue, I have now gone to Champion copper basic plugs gapped at .035. Not honestly sure at this point what the original plugs were but they are all around .050 when I took them out.
- Fuel injectors - new 4 hole K Suspension injectors. The previous ones were unknown brand 4 hole injectors and the plastic nipples were cracked so while I don't think this caused or fixed the issues, I feel better with these being replaced.
- Ignition coil - first swapped with a used but known good coil, did not fix the issue. Ended up installing a new Delphi coil as the original one had some cracking in both the rubber and plastic
- Tested fuel pressure to make sure pump wasn't bad. I am forgetting the exact psi right now but it was in spec.

Thoughts on what I should look at next? O2 sensors or testing the existing ones somehow (pointed that direction from the p0172)? Investigate catalytic converter maybe? Dive further into OBDII live data? Take the head off (dreading that)?

Other things that may be useful:
- Crankshaft position sensor is OEM Mopar and was replaced within the last 3 years
- OPDA was replaced with updated Crown unit, OEM camshaft position sensor was reused. during troubleshooting this issue, we swapped to Crown camshaft position sensor but issue was still present so swapped back to OEM
- Swapped back to OEM PCM (as OEM PCM only had issues on hot summer days and its cold now). Issue still present so swapped back to Wranglerfix PCM. I have also reached out to Wranglerfix to see if they have any suggestions.
- In looking at all of this, we inspected the injector wiring and found some bad wiring on number 4 injector. Bought and installed a new pigtail, I think that was what caused the p0304 and have not seen p0304 since.

Scratching my head a lot and about to find a shop to take it to. Thanks for the help guys.

 

[macleanflood]

Crank position sensor?

-Mac

 

[GATORB8]

Have you checked compression? Maybe burnt exhaust valve?

 

[rublicon]

Have not yet checked compression so I will add that to the list of to dos. One other thing to mention that may be related. We noticed during some of this troubleshooting that when the jeeps seems to be acting up (by that I mean some of the times it has had a flashing CEL, some of the times a code like p0172, and usually a slightly rough idle), there will be a slight knocking noise. I believe that it happens only when the clutch is not pushed in. We used a stethoscope and it seems to be coming from the transmission or likely bellhousing area. My friend wanted me to pull the inspection plate on the bellhousing to look at the flywheel but it looks like you have to remove all of the transmission bolts for that. Could we remove the starter to see if anything is going on in there? If so, what would be the possible culprit there? You would think if there were loose flywheel bolts or something, it would be happening all the time, not just part of the time. Obviously the crankshaft position sensor is down there so maybe it is being affected by whatever might be happening there. I believe a pilot bearing or throwout bearing would make noise only when the clutch is pushed in, not out, and you would think it would happen all the time, not just part of the time.

 

[JKP]

The 6 spd will knock like a box of rocks when idling in N. Not an issue. Push in the clutch, trans stops turning, knocking goes away.

A flashing CEL means misfiring that can result in cat damage.

Dump a can of Techron in the tank and take it out and drive it like you stole it to blow the carbon out.

Also verify your cat to manifold bolts aren't loose.

It's always cyl 1 on my 06 for some reason. The fix above has worked every time. Usually occurred after extended idling waiting in line to get on base.

Currently at 285K mi or so.

 

[Chris]

2005 Wrangler Unlimited Sport 6 Speed Manual with 160ish thousand miles. Had for almost 3 years and about 30k miles. PCM has been replaced with Wranglerfix PCM about 2ish years ago.

Since September, I have been fighting misfire codes, initially a p0301 though at some point of throwing parts at it, I got a few p0304 and p0300. Currently I am no longer getting a misfire code, the only code I am getting is p0172 (system too rich bank 1) but I am still getting a flashing CEL, usually at idle or in stop and go traffic. I believe a flashing CEL implies misfires but it is not storing a misfire code anymore.

I have done the wrong thing by throwing parts at it to see what sticks and am currently at a loss and looking for direction on what to try next.

Here are the things I have done:
- Spark plugs - first did Autolite iridium fine wire something or another gapped at .040. Reading about spark plugs makes me want to shoot myself in the face by the way. To make sure that those plugs weren't part of the issue, I have now gone to Champion copper basic plugs gapped at .035. Not honestly sure at this point what the original plugs were but they are all around .050 when I took them out.
- Fuel injectors - new 4 hole K Suspension injectors. The previous ones were unknown brand 4 hole injectors and the plastic nipples were cracked so while I don't think this caused or fixed the issues, I feel better with these being replaced.
- Ignition coil - first swapped with a used but known good coil, did not fix the issue. Ended up installing a new Delphi coil as the original one had some cracking in both the rubber and plastic
- Tested fuel pressure to make sure pump wasn't bad. I am forgetting the exact psi right now but it was in spec.

Thoughts on what I should look at next? O2 sensors or testing the existing ones somehow (pointed that direction from the p0172)? Investigate catalytic converter maybe? Dive further into OBDII live data? Take the head off (dreading that)?

Other things that may be useful:
- Crankshaft position sensor is OEM Mopar and was replaced within the last 3 years
- OPDA was replaced with updated Crown unit, OEM camshaft position sensor was reused. during troubleshooting this issue, we swapped to Crown camshaft position sensor but issue was still present so swapped back to OEM
- Swapped back to OEM PCM (as OEM PCM only had issues on hot summer days and its cold now). Issue still present so swapped back to Wranglerfix PCM. I have also reached out to Wranglerfix to see if they have any suggestions.
- In looking at all of this, we inspected the injector wiring and found some bad wiring on number 4 injector. Bought and installed a new pigtail, I think that was what caused the p0304 and have not seen p0304 since.

Scratching my head a lot and about to find a shop to take it to. Thanks for the help guys.

Since you have a P0172 code (system too rich), your next best step is to focus on the O2 sensors. A malfunctioning upstream O2 sensor can cause both the rich condition and potentially trigger a flashing CEL due to perceived misfires. If you have access to a scan tool that can read live data, monitor the fuel trims (both short and long) and the O2 sensor voltages. A failing sensor may not show a code until it's really out of spec.

Make sure to inspect for vacuum leaks again. Even a small leak can skew the air/fuel mixture enough to trigger your rich code and affect performance, leading to an idle that feels rough.

While it may not be the first culprit, a clogged catalytic converter can create back pressure issues that affect the engine performance and may contribute to misfires. If you've got a stethoscope, you could try tapping on it and listening for any rattling, which can sometimes indicate internal failure.

Since you had a bad connector on the number four injector, it's worth a thorough inspection of all related wiring and connectors. Any signs of wear, corrosion, or damage could lead to intermittent issues. I can't stress this step enough. Sometimes it involves taking apart the entire wiring harness to find one break in the wiring.

As a last resort if everything else fails, a compression test may not be a bad idea to rule out any internal engine problems.

 

[rublicon]

Since you have a P0172 code (system too rich), your next best step is to focus on the O2 sensors. A malfunctioning upstream O2 sensor can cause both the rich condition and potentially trigger a flashing CEL due to perceived misfires. If you have access to a scan tool that can read live data, monitor the fuel trims (both short and long) and the O2 sensor voltages. A failing sensor may not show a code until it's really out of spec.

Make sure to inspect for vacuum leaks again. Even a small leak can skew the air/fuel mixture enough to trigger your rich code and affect performance, leading to an idle that feels rough.

Check the EGR system for functionality and blockages. If the EGR valve is stuck open or there’s excessive carbon buildup, it can lead to poor idle and roughness.

While it may not be the first culprit, a restricted catalytic converter can create back pressure issues that affect the engine performance and may contribute to misfires. If you've got a stethoscope, you could try tapping on it and listening for any rattling, which can sometimes indicate internal failure.

Since you had a bad connector on the number four injector, it's worth a thorough inspection of all related wiring and connectors. Any signs of wear, corrosion, or damage could lead to intermittent issues. I can't stress this step enough. Sometimes it involves taking apart the entire wiring harness to find one break in the wiring.

As a last resort if everything else fails, a compression test may not be a bad idea to rule out any internal engine problems.

Good point on the harness. We did take it apart, inspect it, and I even ordered a new used plastic tray for it as mine was broken and also a new heat shield kit to go below it as that was missing. I have no knowledge of the O2 sensors and when they were last changed so at the risk of throwing more parts at it, I am tempted to replace all 4 O2 sensors and maybe get another OEM Mopar CPS (having an extra is never bad). Any suggestions on what O2 sensors to go with?

 

[Chris]

Any suggestions on what O2 sensors to go with?

See this post:

https://wranglertjforum.com/threads...r-tj-oxygen-o2-sensor-thread.4068/#post-62696

 

[CharlesHS]

Check the EGR system for functionality and blockages. If the EGR valve is stuck open or there’s excessive carbon buildup, it can lead to poor idle and roughness.

Chris,

The 4.0L does not have an Exhaust Gas Recirculation valve or system installed.
That started with the '07 3.8L to better control exhaust emissions.

 

[Link]

Probably not your issue but worth doing to ensure no issues and costs nothing but time. Clean all your grounds especially the engine ground

 

[rublicon]

Probably not your issue but worth doing to ensure no issues and costs nothing but time. Clean all your grounds especially the engine ground

Also a good reminder. I believe mine are good and have been looked at recently. The strap on the hood was worn through but I was able to reattach it as well.