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Pentastar Misfire on Cylinders 1, 3, & 5


MDuncan

New Member
Joined
Apr 13, 2020
Messages
4
Location
Denver, Colorado
Hi Folks,

Looking for your expertise.

The problem: Random Misfires on cylinders 1,3,5 - Confirmed with Scanner
The Jeep: 2012 JKU 6-Speed, 108K miles
How long: I've been trying to fix this: 9 months

It's hard to feel the misfire when under throttle, but you can hear and feel the slight misfire trembles when at idle.

What I've tried so far:
- New Spark Plugs: (2 set's - 6 NKG & 6 Champion) Properly Gapped
- New Coils: MSD
- New O2 Sensors (all 4 - both sides)
- New Crankshaft Position Sensor
- New MAP Sensor
- All new Rocker Arms and Lifters on that bank (Cyl 1,3,5)
- New Camshaft Position Sensor
- New Injector on Cyl 5 = No change still misfiring
- New upper and lower o-rings for injectors
- New upper and lower o-rings for Lower and Upper Manifolds

Tests Completed:
- Leakdown Test Showed Normal
- Rotated Coils - No Change
- Rotated Plugs - No Change
- Camshafts inspection - no flat spots found

Additional Modifications Possibly Affecting Performance:
Mishimoto Oil Catch Can
Banks CAI
Odyssey Battery

Additional Fixes Completed on Motor:
- New Oil Pressure Sensor


Friends,
Please help. I love my jeep, and I want to drive it to 300k miles and drop in a Hemi and keep driving it.

(Wave),
Matt
 
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Chris

Administrator
Staff Member
Joined
Sep 28, 2015
Messages
32,208
Location
Florence, AZ
First off, congrats on probably one of the most well written, easy to follow posts I've ever seen in all my years running forums. Posts like this actually make people want to help you!

Anyways, I've seen stuff like this before where it seems every logical possibility was exhausted. 9 out of 10 times, it ends up being a wiring issue... yes, a wiring issue.

What I mean by that is a wiring harness that has been rubbing against something and has exposed the wires inside, causing them to short out.

Often times they're in a hard to spot area, but it's usually the last thing people think to look at, when it should be one of the first.

The problem of course is that no one can simply tell you where to look, you just have to be prepared to spend a lot of time tracing the wires.

I would start by looking for any spots where the wires are visibly pressed against the body, frame, engine, etc., then look for wear on the harness itself.

Here's a perfect example of what I'm talking about (look at the wires in the first post):

 
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MDuncan

MDuncan

New Member
Joined
Apr 13, 2020
Messages
4
Location
Denver, Colorado
Thanks, Chris!

Just trying not to waste y’all’s time is all. My gut says you’re likely right with the wiring suggestion. Admittedly it’s also the area I’m most intimidated by. Haha I was more comfortable changing rocker arms...

Still I think I may have been throwing parts at it and praying, but as soon as the sun comes back out here in Denver, I’ll grab a cold one and start tracing lines.

@BLACKJKU I like your idea on the ground. Let me know if anything else comes to mind!

I appreciate it!
Matt
 
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MDuncan

MDuncan

New Member
Joined
Apr 13, 2020
Messages
4
Location
Denver, Colorado
Thanks BLACKJKU - I haven't found and frayed or worn through spots in the wiring.
Talk about frustrating...

I mentioned before that electrical is not my strong spot, but have any of y'all seen a good writeup on how to use a voltmeter to begin working your way through and checking things?

Thanks again,
Matt
 

BLACKJKU

Moderator
Staff Member
Lifetime Supporting Member
Joined
Feb 22, 2020
Messages
2,552
Location
Huntington In
I good wiring diagram would help also, if you could locate the ground points that could be a good place to start. Check to see if the grounds are clean and tight.

It's hard to find anything on the wiring, i've looked before for my Jeep.
 

xackley

JK Enthusiast
Joined
Nov 29, 2019
Messages
117
Location
finger lakes of NY
You haven't said if you have OBD2 codes.
Also have you obtained a scanner
https://www.amazon.com/gp/product/B011NSX27A/?tag=jkforum-20

With very inexpensive software you can monitor the basics of what the PCM(computer) is receiving from sensors and what it is telling the engine to do.
Start out looking at the fuel trims for Bank1 and the O2 readings for Bank1.
Warm the engine, it has to be in closed loop, closed loop means it is using the O2 sensors to adjust the fuel/air mixture.
Long and Short term Fuel trims should be near zero, but may be +-5. More than that and you have a problems
Sensor 1 bank 1 should fluctuate anywhere between 0 and 1 fairly quickly.
Sensor 2 bank 1 should not move much and gravitate toward .7

I do most of my monitoring on a Windows PC with bluetooth and use software name Car Scanner Pro.
You can set up screens with half a dozen or so meters and graphs you can observe in real time.

There is also a screen that displays all the data it can receive from the PCM, which is handy when you start with a shotgun approach to diagnostics. It takes time and investigation to know what the system names and numbers mean.

My jeep had misfire 1,3,5 when switching from open loop to close loop. It sometimes threw a code for O2 sensor voltage High. So the O2 sensor told the computer Bank1 was super rich, the computer not being all that smart, shut off the fuel to the whole passenger side of the engine.
Turned out that just disconnecting the O2 sensor and plugging it back in restored the sensor's communication with the PCM.
Don
 

Artisanau

New Member
Joined
Sep 15, 2020
Messages
18
Location
Australia
Thanks, Chris!

Just trying not to waste y’all’s time is all. My gut says you’re likely right with the wiring suggestion. Admittedly it’s also the area I’m most intimidated by. Haha I was more comfortable changing rocker arms...

Still I think I may have been throwing parts at it and praying, but as soon as the sun comes back out here in Denver, I’ll grab a cold one and start tracing lines.

@BLACKJKU I like your idea on the ground. Let me know if anything else comes to mind!

I appreciate it!
Matt
Matt hi, your the only member I’ve found across all the forums I know of, yet there’s probably more, with almost identical issues as you describe. I notice you seem to have disappeared, but your help and diagnosis might help me out which is what these forums are all about, no? My 3.6 has been into the dealer, they just read the code P0306 misfire on 6 OK, but like you my engine purrs like a cat? So I’m saying to the dealer how can it be a mechanical fault with the cylinder? Your just reading the code and saying we’ll do a cyl leakage test and compression. They didn’t even put it on the tester to determine if it was misfiring on 6 by doing a relative scope test, emissions or anything else that might join the dots. So I’m resigned to fixing it myself maybe with some outside help by using the forums, so if you can give me a heads up how you’ve cured yours I’d be very grateful and I’ll respond by letting you know either way. I to think it’s electrical and I’m thinking PCM soldered joint faults, especially with the high temp Those things endure behind the washer bottle. It seems a mad place to instal it. Most cars I’ve had the PCM is fitted in general to the footwells or underside of the dash areas? I’m hoping you can spare the time to re-engage. Regards Mark in Aus🇦🇺👊
 

Artisanau

New Member
Joined
Sep 15, 2020
Messages
18
Location
Australia
You haven't said if you have OBD2 codes.
Also have you obtained a scanner
https://www.amazon.com/gp/product/B011NSX27A/?tag=jkforum-20

With very inexpensive software you can monitor the basics of what the PCM(computer) is receiving from sensors and what it is telling the engine to do.
Start out looking at the fuel trims for Bank1 and the O2 readings for Bank1.
Warm the engine, it has to be in closed loop, closed loop means it is using the O2 sensors to adjust the fuel/air mixture.
Long and Short term Fuel trims should be near zero, but may be +-5. More than that and you have a problems
Sensor 1 bank 1 should fluctuate anywhere between 0 and 1 fairly quickly.
Sensor 2 bank 1 should not move much and gravitate toward .7

I do most of my monitoring on a Windows PC with bluetooth and use software name Car Scanner Pro.
You can set up screens with half a dozen or so meters and graphs you can observe in real time.

There is also a screen that displays all the data it can receive from the PCM, which is handy when you start with a shotgun approach to diagnostics. It takes time and investigation to know what the system names and numbers mean.

My jeep had misfire 1,3,5 when switching from open loop to close loop. It sometimes threw a code for O2 sensor voltage High. So the O2 sensor told the computer Bank1 was super rich, the computer not being all that smart, shut off the fuel to the whole passenger side of the engine.
Turned out that just disconnecting the O2 sensor and plugging it back in restored the sensor's communication with the PCM.
Don
 

Artisanau

New Member
Joined
Sep 15, 2020
Messages
18
Location
Australia
Hi, I’ve just tried to reach out to MDuncan who you’ve responded to in the past. I am keen to know if he was successful in finding a cure for his 3.6 JK, so I’ll wait to see if he hooks back in to help out.
Xackley, you seem to have a handle on the scanner suggestion. Let me ask you, if my Jeep is throwing out a P0306 misfire on cyl 6 code, do you think it’s probable that it could be the O2 sensor without throwing up a relative fault code. The only o e that is visible is P0306.
Like I’ve said already, the engine purrs, no rough idle, or rough running. Since I replaced the plugs and swapped out the coil, I got like 156 days use out of it without the EML light coming on. Now it’s on between 6 and 9 days an dit seems most apparent when I sitting in traffic that it’ll come on? The only thing I can think of right now is that air flow is reduced over the engine and PCM which seems to get real hot 🥵 in my opinion, maybe that’s how it is but like I said to Matt, most cars I’ve owned prior have their PCM fitted within the interior not the engine bay. I’m going to take the manifold off again, swop out the injector 6 with 1, recheck the wiring underside the manifold. Buy an extension for my compression tester just to have the numbers written down. I done a block test tonight after a run out, no issues like CO% in the coolant, so I’m assuming no cracks. I’m going to buy some new leaks for my fluke and bring it out of retirement, then back probe the inj wires and coil wire to the PCM as I don’t have a wiring map, like you say, as rare as hens teeth and I can’t find one. Failing that I’ll look into the scope you suggest or scanner sorry. I’ll need to do some homework to understand nominal values etc, so I know what I’m looking at to interpret them correctly.
if you think of anything I haven’t mentioned 😂👊 maybe you’d suggest something. All the best to you and the other Jeepers! 👍 Mark.
 

Artisanau

New Member
Joined
Sep 15, 2020
Messages
18
Location
Australia
Hi, I’ve just tried to reach out to MDuncan who you’ve responded to in the past. I am keen to know if he was successful in finding a cure for his 3.6 JK, so I’ll wait to see if he hooks back in to help out.
Xackley, you seem to have a handle on the scanner suggestion. Let me ask you, if my Jeep is throwing out a P0306 misfire on cyl 6 code, do you think it’s probable that it could be the O2 sensor without throwing up a relative fault code. The only o e that is visible is P0306.
Like I’ve said already, the engine purrs, no rough idle, or rough running. Since I replaced the plugs and swapped out the coil, I got like 156 days use out of it without the EML light coming on. Now it’s on between 6 and 9 days an dit seems most apparent when I sitting in traffic that it’ll come on? The only thing I can think of right now is that air flow is reduced over the engine and PCM which seems to get real hot 🥵 in my opinion, maybe that’s how it is but like I said to Matt, most cars I’ve owned prior have their PCM fitted within the interior not the engine bay. I’m going to take the manifold off again, swop out the injector 6 with 1, recheck the wiring underside the manifold. Buy an extension for my compression tester just to have the numbers written down. I done a block test tonight after a run out, no issues like CO% in the coolant, so I’m assuming no cracks. I’m going to buy some new leaks for my fluke and bring it out of retirement, then back probe the inj wires and coil wire to the PCM as I don’t have a wiring map, like you say, as rare as hens teeth and I can’t find one. Failing that I’ll look into the scope you suggest or scanner sorry. I’ll need to do some homework to understand nominal values etc, so I know what I’m looking at to interpret them correctly.
if you think of anything I haven’t mentioned 😂👊 maybe you’d suggest something. All the best to you and the other Jeepers! 👍 Mark.
Apologies for the typos... I did go to school, just never proof read. These damn tablets change and alter the words as you type... must be some Jeep parts inside 😂
 

Artisanau

New Member
Joined
Sep 15, 2020
Messages
18
Location
Australia
Hey Xackley, I just reread your earlier post. If I invested in similar software to you and I’m going to look at the link you gave out next. Would the laptop, retain the information for me to look back on while I’m driving the Jeep around, assuming the EML should come on while out on the road? That suggestion sounds like the way to go. I have access to a laptop running Windows 10, so I’m part way there. The biggest issue is understanding the numbers and values it would be giving compared to what it should be giving. I might be back as someone once said ... cheers!
 
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MDuncan

MDuncan

New Member
Joined
Apr 13, 2020
Messages
4
Location
Denver, Colorado
Hi Artisanau,

Happy to jump back in.

To make sure I understand:
- Your jeep is misfiring on #6 or all cylinders on that bank?

To answer what I have done to my jeep:
Thus far I have not been able to completely cure my misfire(s), but I have tried some additional fixes sense my original Post.

They were:
- Full Engine wire harness @Chris
- Partial wire harness for left bank injectors

I do continue to think my issue is electrical, Fuel, or Intake leak (causing it to run slightly lean). This would all make sense considering you need three things to get an engine running: fuel, air, & spark.


So, in order, what am I going to do next?
- Check fuel pressure from the tank to fuel rail and replace the pump if low pressure is found
- Replace PCV valve
- Replace all breather/intake hoses

What else is going on?
- Well, it just threw P0128 - Thermostat Rationality - Likely the thermostat is stuck open.



Apologies for not being much more help,
Matt
 
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Artisanau

New Member
Joined
Sep 15, 2020
Messages
18
Location
Australia
Hi Artisanau,

Happy to jump back in.

To make sure I understand:
- Your jeep is misfiring on #6 or all cylinders on that bank?

To answer what I have done to my jeep:
Thus far I have not been able to completely cure my misfire(s), but I have tried some additional fixes sense my original Post.

They were:
- Full Engine wire harness @Chris
- Partial wire harness for left bank injectors

I do continue to think my issue is electrical, Fuel, or Intake leak (causing it to run slightly lean). This would all make sense considering you need three things to get an engine running: fuel, air, & spark.


So, in order, what am I going to do next?
- Check fuel pressure from the tank to fuel rail and replace the pump if low pressure is found
- Replace PCV valve
- Replace all breather/intake hoses

What else is going on?
- Well, it just threw P0128 - Thermostat Rationality - Likely the thermostat is stuck open.



Apologies for not being much more help,
Matt
Hey Matt, Saturday morning here with coffee and a reluctance to go again but needs must and I aim to beat this like you.
Yes mines just throwing the code for #6.
Well, I've been through my harness but I'm getting some new fluke leads and back probes and going again.
I intend to swop out the injectors bank for bank although I don't think it's that but while the intake manifolds off its madness not too. I've looked everywhere I can think of, air leaks as suggested on forum which was good?

It's a frustrating issue. I mean the engine runs like a dream, no significant problems other than the EML on for #6?
I was up late last night researching, I'm considering a scanner with Live Data mode. I'm keen to see what happens with the spark signal and fuel voltage on #6 when the light comes on if I don't have any progress this weekend. I intend to speak to a tech expert on these scanners to make sure I get one that'll do the job not just a code reader. I'm intent on spending the $'s collecting tools rather than giving it to the dealer in labour, which too date hasn't worked for me.
Matt, thanks for taking the trouble of re-engaging, it's appreciated. Your post was the closest one I've found anywhere to my own, so yeah, I was keen to know how and what you might have found. So zero as yet like myself😂
Finally, I see on yours I see the issue P0128 thermostat? The weird thing I've nailed down with mine or at least it seems that temp is a related issue. If I was to note one thing it seems like the EML light would come on when mostly at idle in traffic. That said the engine tempt is perfect, so no overheating, fan cuts in as it should? My instincts are saying PCM for the same reason? I can do a good highway trip so opening all avenues for tempt, fuel pressures, sparks, yet she pulls like a train like I just got it from new. I think it was you on your original post that said you want to keep yours even if you have to transplant a V8. I'm the same, I don't want to sell mine regardless. Any other car it would be gone and I used to change my units like every 3yrs due to warranty and business tax but since retirement and buying this as a gift to myself, I just can't part with it. I think I might have something wrong with me, like a 'Jeep Thing' 😂 Hey, kept you too long here, apologies. I'll post progress when and if I get there. If not it'll be a transplant, you do the same, now that'll be something I could take notice of. 👍
 

Artisanau

New Member
Joined
Sep 15, 2020
Messages
18
Location
Australia
Hi team, which specifically goes out to, MDuncan, Xackley and BlackJKU for your recent inputs when I asked for help with mine.

It’s just a brief update in case you were wondering if I’d solved the issue of the misfire P0306 so on #6 without letting on.
In short not yet. I’ve ordered a bi-directional scanner, specific to Chrysler Jeep, hasn’t arrived yet but anticipate it’s arrival anytime.
Not having one for the time being and reading what you Xackley wrote re’ your O2 sensors, I took the initiative and done the same but in doing so I did make a rookie error, after reading even more on sensors etc. I disconnected all 4, sprayed protective lube into sockets before refitting. Ran like a dream for 15km, but when parking to shop, lumpy rough running all over the place. Not being able to identify and do much at the time, I came back to it after an hour, drove the JK back home which was ok with an intermittent miss here and there, but by the time I’d reached home it ran perfectly again. The EML light was on but this time no code was thrown? Before I go off point, what I read was, was that the 4 wire O2 sensors vent to the atmosphere between the signal wires and protective sheath unlike the 2 wire earlier version which has a small hole in the actual sensor screwed into the manifold.
Hope that helps someone out at least, apologies if that’s common knowledge. In short the erratic running after disconnection and connection of the O2 sensors was self inflicted and the spray lube was interfering with the sensors obviously, Whoops!
While I’m waiting for the box of tricks, I also done a block test just to establish wether or not there’s CO2 in the water jacket, thankfully, a negative, so some good news, we’ll very good!

I’m not sure it’s cured, but it’d be a relief without doubt, but as yet, no code thrown except to say I’ve noticed the tailpipe to be sooted up rather than the clean tan colour it always has been, so running rich, but not so I’d notice in relation to km/litre, all seems good still?
The scanner is always going to be a good addition to the tool box regardless and I n response to Xackley’s previous suggestion I have downloaded the ‘Car Scanner Pro’ he suggested as an additional back up to the ordered scanner. I’m just waiting for the Bluetooth adapter in addition. What I liked about that and what the demo showed was the parameters to look for but in the far right column, the system tells you wether the component test has passed or failed.
I understand that these are for guidance and should direct you and not always be taken literally and that you need a fairly comprehensive knowledge of how all the sensors work in unison with each other and what each one is responsible for, otherwise you’ll just keep throwing parts to the problem still without fully understanding why... even with a scanner.

Cheers guys, I’ll report when and if I learn more. I’m making an effort to see this through to the end, because my internet experience in finding the info I’m specifically looking for is somewhat disjointed. The authors don’t always reiterate the complete facts and the suggestions to a final solution are generally inconclusive if the issue is not found to be a plug or coil.
 
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JKU_momma

New Member
Joined
Dec 2, 2020
Messages
2
Location
Fairfield, Ohio
Hi Artisanau,

Happy to jump back in.

To make sure I understand:
- Your jeep is misfiring on #6 or all cylinders on that bank?

To answer what I have done to my jeep:
Thus far I have not been able to completely cure my misfire(s), but I have tried some additional fixes sense my original Post.

They were:
- Full Engine wire harness @Chris
- Partial wire harness for left bank injectors

I do continue to think my issue is electrical, Fuel, or Intake leak (causing it to run slightly lean). This would all make sense considering you need three things to get an engine running: fuel, air, & spark.


So, in order, what am I going to do next?
- Check fuel pressure from the tank to fuel rail and replace the pump if low pressure is found
- Replace PCV valve
- Replace all breather/intake hoses

What else is going on?
- Well, it just threw P0128 - Thermostat Rationality - Likely the thermostat is stuck open.



Apologies for not being much more help,
Matt
Any luck on finding the problem yet? I am having the exact issue and have replaced all of the same parts in addition to both of my catalytic converters because the misfire eventually caused my passenger side cat to fail. This thing is driving me nuts 😫
 

Artisanau

New Member
Joined
Sep 15, 2020
Messages
18
Location
Australia
JKU_momma, I think so?

I thought I’d posted an update especially for the guys who were responsive to me at the time of my issues, but looking back I think not. Anyhow, in short because of how well it was running and not having the correct tools at the time, it was easy to overlook the basics.
I received the scanner, noticed trims running slightly rich. Found no leaks with smoke tester and no CO2 in water. Popped the intake manifold, compression test revealed low on #6 and 30% loss on leak down test. So interacting with Jeep to see if they’ll honour a repair and still waiting for a response, but its Dec and with Covid, I could be waiting a while as with everything else. I’ll have no option but to do it myself if I get a negative reply. The issue will be finding a new head thats not re-worked which there seems to be a lot of.