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Discussion Starter · #1 ·
My TJ had a rough idle and low mpg for about a month with no code. I changed the spark plugs and that did not fix anything. Plugs 4-6 were dirty when I changed them. Once I drove the Jeep on the highway for about 45 min I got a flashing check engine light. The light came on for P0174 and P0306. They were the only codes showing, no P0171. I cleaned the throttle body, replaced the throttle body gasket, and changed the B2S1 oxygen sensor (NGK). Still no change. I then checked the Cylinder 6 spark plug and it was sooted. The spark plugs had maybe 100 miles on them. I swapped the Cylinder 6 spark plug with the Cylinder 2 spark plug and the P0306 code went away but the P0174 was still there. I decided to unplug my battery overnight to try and reset the PCM. That did not fix anything and the P0174 came back after about 20 miles. At idle, the B2S1 O2 sensor fluctuates between 0.1 and 0.5 Volts and the B2S2 O2 sensor stays at 0.1V. I sprayed some carb cleaner into a vacuum line and both bank 2 sensors went rich (0.9V) so I believe the sensors work. The LTFT1 is about 8% and LTFT2 is around 20% at idle. When driving they go to 0-3%. Both STFT's are fluctuating at the same rate. I have checked the fuel injectors with a stethoscope and they are all clicking at the same rate. I have done a smoke and carb cleaner test on the intake vacuum lines and cannot find a leak.

I am stuck on what to check next. I am thinking it could be an exhaust leak or bad wiring form the PCM to the B2S1 O2 Sensor from reading other threads. How would I check for an exhaust leak or bad wiring from the PCM? Is there anything else it could be or that I should test?
 

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P0174 is LEAN B2.

I am guessing those fuel trims are + ? If the trims are showing +.
The 20% is a high adjustment.
knee jerk suspect - the .1 to .5 is lean so I'm thinking a clogged inj.
Start with adding a can of 'seafoam' to start.
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I see you have a scanner and live data - rechek the fuel trims confirm + adjustment.
POST live data - ECT, TPS, MAP, and again the o2 readings. Add B1S1 volts.
What plugs did you use - brand and #.

What year TJ?
 

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Discussion Starter · #3 ·
Yes the fuel trims were positive. I added a can of seafoam last time I filled up the gas tank. Is there a better place to add it or should I just add more?

I can get the live data and spark plug information in a few days. The TJ is a 2005.
 

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1 cqn should do it.
Look at and post the live data IF yu can check the freeze frame MAYBE a clue.
 

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Discussion Starter · #5 ·
Here are some old photos I found. The live data was screenshotted from a video so let me know if there is anything else from the live data that would be useful. The live data that has the LTFTs at zero is from me pressing the throttle. The freezeframe is from when i first got the code.
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Discussion Starter · #7 ·
I got the cylinder 6 misfire code again. I decided to test my coil pack and I got no spark from the cylinder 6 coil. When I did a resistance test on the coils though all of the coils had 15k ohms. Should I replace the coil pack or could it be another issue?
 

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Seams we are getting nowhere SO I am regrouping.

First thought I would have for a P0306 - details matter
PLUGS (ZFR5N NGK) .030-.035 gap -
how did #6 look Wet, Black, Dry, Tan damaged
> I am not thinking a coil as #1 would likely code also. FYI - coil RAIL
What is the TPS voltage at idle.
Do you have a DVOM?

I am rereading the postss checking the live data you posted and tem looking at TSB's -

Take note FUEL PRESSURE 58psi +- 2
 

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Discussion Starter · #9 ·
Seams we are getting nowhere SO I am regrouping.

First thought I would have for a P0306 - details matter
PLUGS (ZFR5N NGK) .030-.035 gap -
how did #6 look Wet, Black, Dry, Tan damaged


What is the TPS voltage at idle.
Do you have a DVOM?

I am rereading the postss checking the live data you posted and tem looking at TSB's -

Take note FUEL PRESSURE 58psi +- 2
I unplugged the fuel injector for cylinder 6 and the idle stayed the same. Unplugging the other injectors made the idle worse. So I definitely think it is a cylinder 6 issue.

The plugs are Champion Double Platinum. All of the plugs sparked except for when I plugged them into coil 6. I replaced the coil with an “Ultima Select Wires Coil-On Plug Boot” and nothing changed. Plug 6 had some black on it but for the most part looked to be in good condition; like I said it sparked on the other coils.

I have a multimeter so I can check the TPS voltage later today.

I dont have a schrader valve on my fuel line thats the only reason I havent checked fuel pressure yet.

With this info do you still think I should check fuel pressure and pull the injectors? What all would I need to check fuel pressure?

I am adding some new Live data from yesterday it is a little different from what I was seeing before I reset the PCM. The first set of Live data is from driving on the highway and the other set is at idle at driving on the highway. O2 sensors 1&2 are the upstream&downstream sensors for bank 1. O2 sensors 5&6 are the upstream&downstream sensors for bank 2.
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The plugs - platinum - not a preferred type AND they are more $$ than spec plugs, I suggest you recheck the plug compatibility.

You removed the inj connectors - did you generate any codes? thinking p0201 thru P0206, code may be in pending.

A thought - with #6 inj connected engine running is there voltage BOTH wires, and try unplugging the connector with a test light the light should flash ?
 

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The plugs - platinum - not a preferred type AND they are more $$ than spec plugs, I suggest you recheck the plug compatibility.
The double-tipped platinum plugs are NOT the issue nor are they ever an issue. MANY prefer them over conventional spark plugs so for many they are preferred, me included. They outlast conventional spark plugs by 3-4X and the fine wire technology used by the double-platinum and iridium tipped plugs make it easier for the plugs to fire in difficult combustion conditions. The ONLY platinum plug that causes a problem in newer 4.0 engines is a single-tipped platinum plug which he already verified he is not running.
 

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My kneejerk platinum = bad.
Yes my bad - DOUBLE should be fine with waste spark TKS jerry.
trying to get some headway on issue -
 

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Discussion Starter · #13 ·
It ended up being the coil pack. I replaced it with one from the junkyard and swapped the pins on the connector bc the coil pack came from a Pre-2000 Jeep. After correctly installing the “new” coil pack the misfire went away and the jeep ran awesome.
 
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