Engine Running Rough at Operating Temp

[CODE5]

I'm asking for a little guidance here... I think I'm dealing with a case of heat soak, BUT I want to be sure it isn't something else like a bad upstream o2 sensor or bad catalytic converter... OR all of the above, haha.

First off, I have a CEL for various vacuum leaks - always have since I bought it last year: P0422 and P0455. I've gone through several gas caps, and checked my vacuum lines in the engine bay. The only place I haven't checked is at the actual fuel lines going into the gas tank.

Additionally, whenever the Jeep is running, there is a gas smell. It's not like raw gas; it's like the Jeep is dumping tons of fuel through the exhaust (which I've noticed the bad fuel economy). This has me wondering if my pre-cat o2 sensor is giving me trouble.

I've noticed that the Jeep runs/drives great at the beginning of the day (before the engine temp reaches the operating level of 210F). On drives longer than 30 mins or once the engine hits about 210F when I come to a stop, I notice the idle feels very odd - like a skip, BUT I don't have any misfire codes... By Odd, I mean it seems rough, very low 640-650 rpms.

If I turn off the engine and hop back in while it is at operating temp. it does take more effort to crank (sounds like heat soak)

So... Is there a good way to somehow test the upstream O2 Sensor since I've read it controls the Air/Fuel mix and COULD be my culprit? I'm pretty sure I need fuel injectors since I'm seeing signs of cracking from the heat - my TJ didn't come with the heat shield around the exhaust manifold like the ones I've seen on here... The motor is not original (50,000 miles); however body/exhaust is at 200,000 mi.

Any help is appreciated!

 

[Painfultruth]

Scanner live data:

Look at your fuel trims and 02 sensor voltages.

 

[CODE5]

Scanner live data:

Look at your fuel trims and 02 sensor voltages.

This was idling in my driveway not sure what the engine temp was at the time.

 

[Painfultruth]

It must be running at operating temp so the system enters into closed loop mode. Have a look at both short term and long term trims at 1200-1500 rpm.

 

[macleanflood]

My money's on a cracked exhaust headers. Gets hot and the crack gets bigger. Not all the exhaust is making it to the O2 sensors so they say more fuel!

At least that was my problem and Banks headers were my solution.

-Mac

 

[CODE5]

My money's on a cracked exhaust headers. Gets hot and the crack gets bigger. Not all the exhaust is making it to the O2 sensors so they say more fuel!

At least that was my problem and Banks headers were my solution.

-Mac

I don’t have any kind of additional noise in the engine bay and I don’t smell fumes in the cab, only from the rear when I’m behind the muffler. I did notice all my O2 sensor have been replaced - they look to be BOSCH so that might be my problem. Going to run a test tomorrow and get some screen grabs when the engine gets to operating temp and runs off the upstream O2 sensors

 

[MikeE024]

I don’t have any kind of additional noise in the engine bay and I don’t smell fumes in the cab, only from the rear when I’m behind the muffler. I did notice all my O2 sensor have been replaced - they look to be BOSCH so that might be my problem. Going to run a test tomorrow and get some screen grabs when the engine gets to operating temp and runs off the upstream O2 sensors

Fwi, I’ve tested for exhaust leaks via two methods.

(1) duct tape a shop vac to pressurize the system through the tailpipe. Then spray soapy water on the manifold/headers.

(2) hook up a pressurized smoke tester that utilizes shop air.

 

[Painfultruth]

I don’t have any kind of additional noise in the engine bay and I don’t smell fumes in the cab, only from the rear when I’m behind the muffler. I did notice all my O2 sensor have been replaced - they look to be BOSCH so that might be my problem. Going to run a test tomorrow and get some screen grabs when the engine gets to operating temp and runs off the upstream O2 sensors

Yes, you’ll need to get the correct 02 sensors before trying to troubleshoot any further. The system requires PWM 02 sensors. NTK’s will work correctly.

During your test negative fuel trims will also be a good indicator of the incorrect 02 sensors.

 

[CharlesHS]

Read this thread concerning O2 sensors this will provide you the proper PNs for your year TJ.

https://wranglertjforum.com/threads/the-official-jeep-wrangler-tj-oxygen-o2-sensor-thread.4068/

 

[CODE5]

So with the BlueDriver scan tool I can export out a CSV of my readings... this was from a drive where the engine got to temp... Looks like negative fuel trims...

Dropbox link to PDF

 

[CODE5]

Once the engine got around 1,000 rpm and up the short trim become much more negative. (Cutting fuel to the injectors - running rich)

 

[Painfultruth]

Once the engine got around 1,000 rpm and up the short trim become much more negative. (Cutting fuel to the injectors - running rich)

View attachment 407798

You’ll need the LTFT as well, it’s your baseline. The STFT shown is consistently pulling fuel, but the amount isn’t really that much, the two together will give a better picture.

Again, those Bosch sensors if not the complete problem are almost certainly part of it.

Edit: I’m not sure if the Blue Driver will show 02 heater voltages, but if so have a look at them as well. If the heater circuit isn’t working properly it will cause the appearance of a rich condition, and subsequent negative trims.

 

[MikeE024]

My money's on a cracked exhaust headers. Gets hot and the crack gets bigger. Not all the exhaust is making it to the O2 sensors so they say more fuel!

At least that was my problem and Banks headers were my solution.

-Mac

Were you getting codes when this happened?

 

[Jerry Bransford]

Your symptoms, the problems happening when the engine is warmed up, mostly indicate a bad upstream O2 sensor or two. Cracked manifolds/vacuum leaks/etc. would cause problems when the engine was cold too.

If you decide to replace the upstream O2 sensor(s) make sure to ONLY go with NTK, NGK, or Mopar with NTK being the manufacturer of all of those. Avoid store brands and above all avoid Bosch whose O2 sensors don't work well in our Jeep.

 

[CODE5]

Your symptoms, the problems happening when the engine is warmed up, mostly indicate a bad upstream O2 sensor or two. Cracked manifolds/vacuum leaks/etc. would cause problems when the engine was cold too.

If you decide to replace the upstream O2 sensor(s) make sure to ONLY go with NTK, NGK, or Mopar with NTK being the manufacturer of all of those. Avoid store brands and above all avoid Bosch whose O2 sensors don't work well in our Jeep.

That is what I'm thinking as well... I do know I have a vacuum leak somewhere in the system. I'll clear it and then once the computer runs its test at the various fuel levels it comes back - P0442 / P0455.

 

[MikeE024]

That is what I'm thinking as well... I do know I have a vacuum leak somewhere in the system. I'll clear it and then once the computer runs its test at the various fuel levels it comes back - P0442 / P0455.

Pressurized smoke test will find the vacuum leak.

Fwiw I was running year old NGK o2 sensors and replaced them with new after running lean from a vacuum leak and dumping fuel on them. The system works much better now.

 

[hear]

Pressurized smoke test will find the vacuum leak.

Fwiw I was running year old NGK o2 sensors and replaced them with new after running lean from a vacuum leak and dumping fuel on them. The system works much better now.

Any guides on how to do this test? I’ve only ever seen the cigar trick and it doesn’t seem to work well for me.

 

[macleanflood]

Were you getting codes when this happened?

Yes but not related to the cracked headers. My Jeep was a miasma of neglect and cheap store parts. I was getting misfire codes that turned out to be a CPS and my oil pressure sensor took a couple of tries before I got a Mopar one.

-Mac

 

[Jerry Bransford]

Any guides on how to do this test? I’ve only ever seen the cigar trick and it doesn’t seem to work well for me.

There are diagnostic smoke generators available, I'd call your local parts stores.

 

[Painfultruth]

A vacuum leak will cause positive fuel trims and add fuel.

Negative fuel trims are not caused by manifold leaks, restricted air intake, restricted exhaust, catalyst failure, bad 02 sensor or wiring, fuel pressure, leaking fuel injectors do.