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.

 

[rublicon]

Hey guys, I have an update and more questions on my issues. It has taken time but the Jeep is in the best running shape it has been since maybe August. After trying to chase down and fix both the misfire codes and the flashing check engine light, I have replaced spark plugs twice (landed on copper Champion plugs), replaced the coil (with a Delphi), replaced the injectors (with K Suspension 4 hole bosch), inspected and fixed some injector wiring, replaced the injector harness tray and heat shield, replaced all 4 O2 sensors (with NGK), verified the front cats are in good condition (Jeep has 160k miles and someone replaced the front cats with MagnaFlow before I bought it at 130k miles), gutted the factory rear cat (which did not show light in about 50% of the holes when checking with a flashlight).

I have been driving it for the last 2 weeks and it runs great nearly all the time with a couple of exceptions:
- No codes have been permanently stored in the last 2 weeks but sometimes it will have pending p0172 or p0175 codes (light does not come on, I just happen to check periodically with my reader).
- Every now and then when stopped at a light or stop sign, it will seem to run a little rough and have a knocking like noise. This is a manual and if I push the clutch in, the knocking noise goes away but the roughish idle is still present. On a couple of occasions, the CEL will flash while this is happening but no code is pending or stored, just a temporary flashing CEL. We used a stethoscope when it was knocking and the part that it seems the loudest from is the bellhousing.

I am not terribly concerned about the p0172 or p0175 (or for that matter, any emissions related code) currently but I would like to resolve both the flashing CEL and the knocking sound. It seems to only do this when it is warmed up on a warm day. My friend has suggested maybe the flywheel bolts are loose and its causing the CPS to get bad readings. One thought I had is what if my timing is just a little bit off. I have replaced the OPDA with the Crown unit and at the time, went through the process of setting it by finding top dead center but maybe I should revisit that. Other things of note are that I have replaced the CPS with a Mopar unit a couple years ago. It is currently using the factory camshaft position sensor instead of the one that came with the Crown OPDA.

Thoughts, suggestions? Any 4.0 gurus out there that can magically solve this issue?

 

[Link]

Flashing check engine light is not something to ignore. They are rich running codes on both banks. I’d be looking at your fuel pressure and if that’s good, I’d be suspicious of your injectors.

 

[rublicon]

Flashing check engine light is not something to ignore. They are rich running codes on both banks. I’d be looking at your fuel pressure and if that’s good, I’d be suspicious of your injectors.

We checked fuel pressure and it is in spec, I forget the exact reading but 56, 58, something like that. The injectors were one of the first things I replaced. The previous set was unknown Chinese 4 hole injectors that had been fine for a couple of years. When I started getting misfire codes, the first thing I did was replace spark plugs, and then injectors. Bought K Suspension 4 hole Bosch injectors and installed them. Wondering if timing (OPDA) being a little off could cause rich conditions.

I still find it super weird that the CEL will flash but show no codes, pending or confirmed.

 

[CharlesHS]

Shortly after purchasing my Jeep the vehicle was plagued with random misfires; I too replaced the spark plugs and fuel injectors and installed the manifold shield and injector insulators which only slightly improved the random misfire problem.
I had a problem with the throwout bearing going bad so I replaced the clutch, pressure plate, flywheel, etc.
During the replacement we found the triggering blocks for the CPS signal had rust on them and the CPS surface also had rusty dust on it.
After the replacement of the flywheel and cleaning the CPS surface; the random misfires almost totally disappeared.
A long time technician suspected that the rust was interfering with the hall effect for the CPS.
Something to consider would be to remove the CPS, clean the surface and inspect the triggering blocks surface for rust.

 

[sab]

I am not terribly concerned about the p0172 or p0175 (or for that matter, any emissions related code) currently...

Flashing check engine light is not something to ignore. They are rich running codes on both banks. I’d be looking at your fuel pressure and if that’s good, I’d be suspicious of your injectors.

Listen to Link. P0172 and P0175 indicate that your both of your engine's upstream oxygen sensors are indicating the exhaust is rich (more fuel than is burnable). If it's excessively rich, your expensive new cats can be clogged prematurely. Those aren't simply emissions-related codes. They mean your engine is using too much fuel because something is wrong. You need to download the Powertrain Diagnostic Procedures Manual from the Jeep Wrangler TJ Factory Service Manuals (FSM) & Technical Documentation Thread in the TJ Resources forum. It's packed with good info. Go to page 95 (pdf Page 103) and read up on those DTCs and how to troubleshoot them.

It seems to only do this when it is warmed up on a warm day.

If you look at the Powertrain Diagnostic Procedures Manual, look at the "When Monitored" and "Set Condition" sections. In the "When Monitored" section, it states that it's monitored, "With the engine running in closed loop..." The engine only runs in closed loop when it's warmed up. When cold, it runs in open loop (just uses a look-up table for injector pulse width based on basic sensors). The fact that it's running poorly only when warmed up makes me think the problem is related to running in closed loop. Closed loop means it's adjusting injector pulse width (the amount of time the injectors are opened for each cycle of the engine) based on the O2 sensor values. So, it's detecting too much fuel and reducing the pulse width. This is where the "Possible Causes" and the test chart in the Powertrain Diagnostic Procedures Manual can help you diagnose the problem.

Even before that, though, I'd take a look on your code reader at the short term and long term fuel trims with the engine warmed up, especially when it's running poorly. I don't know what the NGC PCM uses for a maximum short or long term fuel trim, but it's usually 20-25% for long term. If you see it maxed out, you really need to figure things out because the excess fuel may be enought to quickly destroy your cats.

In the "Set Condition" section, it states that, "If the PCM multiplies short term compensation by long term adaptive and a purge fuel multiplier and the result is below a certain value for 30 seconds over two trips, a freeze frame is stored, the MIL illuminates and a trouble code is stored." What that means is that it's reducing pulse width more than what it considers "normal," so it triggers the trouble codes. The reason it's staying pending seems to me to be because it takes two consecutive trips for the code to promote from pending. It must be intermittent enough that you haven't had the problem where it was below the limit for 30 seconds over two consecutive trips. Perhaps if you start it up, let it warm up, and then sit idle running roughly for over 30 seconds, then shut it off, re-start, and let it idle again running roughly for over 30 seconds, it'll promote and trigger the MIL (check engine light).

The fact that you're seeing both P0172 and P0175 indicates that the problem is related to all cylinders, so it's not a single injector, spark plug, etc. It's something that affects all cylinders. Looking at the "Possible Causes" these are the ones that would affect all cylinders (I didn't circle engine mechanical problem because I think that's unlikely, but technically could be a cause), so concentrate on them:

 

[sab]

Wondering if timing (OPDA) being a little off could cause rich conditions.

Not likely, but possible. But if timing was off, you should see a DTC for that.

I still find it super weird that the CEL will flash but show no codes, pending or confirmed.

This is usually caused by a very intermittent misfire. The PCM continuously runs a Misfire Monitor that compares cam and crank signal pulses, so it can determine very small misfires. However, it's possible for a code to never be set by the PCM if it's intermittent enough. The PCM won't set a code for a single, or small number, of miss(es). It's possible you have multiple problems - one causing the rich condition and one causing the misfires.

 

[Link]

We checked fuel pressure and it is in spec, I forget the exact reading but 56, 58, something like that. The injectors were one of the first things I replaced. The previous set was unknown Chinese 4 hole injectors that had been fine for a couple of years. When I started getting misfire codes, the first thing I did was replace spark plugs, and then injectors. Bought K Suspension 4 hole Bosch injectors and installed them. Wondering if timing (OPDA) being a little off could cause rich conditions.

I still find it super weird that the CEL will flash but show no codes, pending or confirmed.

Good info above this post.

Injectors can be bad even if new so you can’t rule them out at this point.

Doubt your OPDA is causing your issues.

 

[AndyG]

Check your “L” shaped vacuum boots on the intake manifold. They fry.

 

[sab]

Check your “L” shaped vacuum boots on the intake manifold. They fry.

While that would cause it to run poorly, it should cause a lean, not rich, mixture.