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Old 08-20-2019, 07:46 AM
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Multiple cylinder misfire, any suggestions?

2012 JK 149K
Left cylinder head replaced under warranty last winter.
I have misfires only on the right head.
It can be multiple cylinder misfires (1,3,5,) or more commonly just one cylinder misfiring (1, 3, or 5), currently only cylinder 1 is misfiring around 200-250

Repairs and checks:
The head is good with a leakdown test of 2% on cylinder 1, 3, and 5
Swapped coils (no change)
Checked wire harness connectors (clean)
Listen to injector clicking
Seafoamed (twice)

New spark plugs
New right bank cam sensor
New idler pulleys (2)
New o2 sensor

Each time a repair has been attempted the engine light stays off for a week or two then comes back on.

I'm ruling out mechanical because cylinder 1, 3, or 5 can at times run perfect with no misses, other times there is a misfire. Its random can be any of the cylinders on the right bank. If it were a fuel pump or filter it would misfire on both heads.

Anyways, this is where I'm at, any suggestion? Thanks in advance for your help.

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Old 08-20-2019, 07:19 PM   #2
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Have the injectors been cleaned or replaced? And exactly what codes are being thrown?

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Old 08-21-2019, 08:02 AM
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Code is currently P0301, although it changes after a fix attempted and clear codes to 303 or 305. Once it came back as 300 multiple cylinder misfire.



The injectors haven't been cleaned or replaced. It would seem if an injector is dirty, its dirty, and stays that way until cleaned. Each injector on the right bank has proven to work as it should without any issues or misfires.



At this time injector 3 and 5 are running without any misfires going on three weeks. If I clear the codes chances are it will come back as a 303 or 305 code and injector 1 will work as it should for however long I run it until I clear the codes again. I'm having a hard time believing it is a injector problem when all three have shown their working as they should.
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Old 08-22-2019, 01:35 PM
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145 views....I was hoping for more feedback.
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Old 08-22-2019, 02:38 PM   #5
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145 views....I was hoping for more feedback.
True. But apparently there aren't too many people here, who are working on their JKs. Well, perhaps other than installing some DIY aftermarket parts or kits.

Other than that, sounds like you have already covered most angles. You may try swapping injectors between heads, but I doubt this would be it.

Did you check freeze frame data, to see what are the parameters when this occurs? What rpms?
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Old 08-22-2019, 07:12 PM   #6
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You are getting into more drivability type diagnoses and you generally don't get that on forums. Usually it involves more complicated tools and know how.

But here is what I would look at.

Do you have a scan tool? I don't mean a cheap code reader, I mean one where you can see module level live data? We are lucky that JSCAN can show you most of that at a really cheap price. I would hook up a scanner and look short term and long term fuel trims and o2 sensor data. The names on JSCAN are slightly different than what I have seen on my snap on scanner but they are called something like o2 B1S1 ADAP or something to that effect. I would concentrate on the bank that is having the misfires (even compare it to the good bank). I would look to see if it's running lean or running rich. If the bad bank is running lean, you are probably not getting enough fuel. Maybe suspect a bad fuel injector or PCM/wiring is not allowing the injector to trigger. If it's running rich, could be an a coil is not firing all the time. Or could be other items.

Also another method a pro (or DIYER with lots of tools) with proper tooling might do is use a scope and scope out the injectors or coils and see what they are doing electrically when they are being triggered. You might find a coil or injector that has issues when it gets hot, could be a suspect control wire or power wire to the coil or injector that was pinched or scraped under the intake manifold when it was installed.

Lots of different ways this could go. You need scanners and scope to help determine and refine the direction to go in.
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Old 08-22-2019, 07:22 PM   #7
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You need a scan tool to diagnose this issue. Either your dealer or a trusted shop.

Where are you located?
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Old 08-22-2019, 07:53 PM   #8
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Originally Posted by SACJ5 View Post
If it were a fuel pump or filter it would misfire on both heads.
By the way, this may appear logical, but in short, that is not always how it works out in real life.

Try to get access to the freeze frame data records. These are stored automatically as the issue is reported (CEL) and can later be accessed via a good scan tool.
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Old 08-23-2019, 07:08 AM
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I have a Launch CR319 code reader I don't believe I have access to freeze frame data records, it has freeze frame and live data I'll have to check if I can retrieve the records.



The codes were cleared yesterday and misfires are down as of this morning, cylinder 1 only had 2 misfires and #3 had 20. Drove it hard on the highway yesterday along with adding seafoam to the oil and and tank.



I did find a slight improvement on misfires when I seafoamed the intake a while ago went from 200 misfires to 100. I did scope the #1 piston yesterday and the carbon didn't look bad for the mileage but I couldn't see the valves with the scope I was using.



I'm not saying carbon is the problem but after a cleaning the misfires go down and the engine performance improves. I'll add a quart of MM to the oil at 150k as well.
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Old 08-23-2019, 09:08 AM   #10
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I did scope the #1 piston yesterday and the carbon didn't look bad for the mileage but I couldn't see the valves with the scope I was using.
For clarification, when I referred to scope, I was speaking about an oscilloscope not a borescope. The oscilloscope allows you to look at the electrical signature, both voltages and amperage draws, for electrical/mechanical devices. Especially useful when you have coils and injectors sitting under the intake manifold. You can tap into the wires coming out of there or even at the PCM.
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Old 08-23-2019, 10:37 AM
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I understand the difference.



My scope inspection was to check for carbon. I used my scope to look into the cylinder to inspect for carbon buildup on the valves and piston head.
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Old 08-23-2019, 11:16 AM
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If the light comes back on I'm pulling the valve cover to inspect for worn parts.
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Old 08-30-2019, 08:53 AM
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Engine light came back on, misfire on cylinder 5. Ordering some parts and pulling the valve cover.
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Old 08-30-2019, 08:58 AM   #14
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Engine light came back on, misfire on cylinder 5. Ordering some parts and pulling the valve cover.
What parts are you ordering?
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Old 08-31-2019, 06:15 AM
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What parts are you ordering?
Before I remove the valve cover I'll purchase 12 rocker arms, VC gasket and a PCV. I figure any other mechanical parts under the cover would show up on my vacuum reading if they were bad (vac needle was steady at 19").



Whatever rockers I don't need I'll return. I know bad rocker bearings can and do cause misfires. However, I've heard 3.6 ticking/tapping and mine isn't sounding anything like that. I won't know for sure until I remove the cover for inspection. I will replace the PCV first and clear the codes before removing the valve cover.



"A STAR Case bulletin, S1309000016, was released just over two years ago (March 18, 2014) in regards to the rocker arms used in the Pentastar® engine. The symptom/vehicle issue is ticking/tapping noise from the upper engine area. In addition, this failure can also set a Diagnostic Trouble Code (DTC) for an engine misfire."
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Old 09-16-2019, 07:27 PM
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Replaced all 12 rockers and cleared the codes. I'm still having a misfire on cylinder 1 (20-50) however, the engine light is currently not on.
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Old 09-16-2019, 08:04 PM   #17
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I would just replace the head :|

The reason they replace the 2,4,6 head and not the passenger side is because the driver's side head runs hotter (on the return side of the coolant flow). This causes the valve seats to go quicker. Both can have the same failure. That's just an opinion of course.
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Old 09-17-2019, 09:19 AM
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I would just replace the head :|

The reason they replace the 2,4,6 head and not the passenger side is because the driver's side head runs hotter (on the return side of the coolant flow). This causes the valve seats to go quicker. Both can have the same failure. That's just an opinion of course.
I'm thinking you miss this?
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Originally Posted by SACJ5 View Post

Repairs and checks:
The head is good with a leakdown test of 2% on cylinder 1, 3, and 5

Now to go along with the good sealing valves it now has 12 new rockers. The new rockers seemed to help, I haven't had any misfires on cylinder 3 or 5 since the install, only on cylinder 1.



Saturday, after using my winch the engine light came on with 100 misfires on cylinder 1. I believe the cause was in part, or because of the low idle while using the winch. I cleared the codes and will check for misfires going forward.
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Old 09-24-2019, 09:14 AM
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The engine light came back on again after getting bogged down a bit in sand. I found 100 misfires on cylinder 1. The engine light went out on its own a day later. The symptoms have narrowed down to cylinder 1 only and when the engine idle drops. Both times the engine light came on when winching and driving offroad.

I already preformed a leakdown test however, I will do a compression test to be thorough. If it tests good like I believe it will I'll swap out the crankshaft sensor to see if that will help.
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Old 09-30-2019, 01:26 AM   #20
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The reason they replace the 2,4,6 head and not the passenger side is because the driver's side head runs hotter (on the return side of the coolant flow). This causes the valve seats to go quicker. Both can have the same failure. That's just an opinion of course.
Both sides are getting equal coolant flow. There is NO return side.




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Old 09-30-2019, 05:35 AM   #21
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I'm thinking you miss this?



Now to go along with the good sealing valves it now has 12 new rockers. The new rockers seemed to help, I haven't had any misfires on cylinder 3 or 5 since the install, only on cylinder 1.



Saturday, after using my winch the engine light came on with 100 misfires on cylinder 1. I believe the cause was in part, or because of the low idle while using the winch. I cleared the codes and will check for misfires going forward.
So low idle and winch use trigger the problem? Sounds like low alternator output. Low enough once in a while that the coil can't store enough energy to produce a good spark. Check your alternator output and battery before you throw any more parts at it.
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Old 10-01-2019, 09:20 AM
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I don't feel I'm throwing parts at this problems in fact, I feel I've been conservative when it comes to buying parts. The parts I've changed, (besides the cam sensor), were due for maintenance.



The 12 new rockers have solved the misfire problems as daily driving is concerned I currently have no misfires on cylinder one and the engine is running smooth.


I still have to put the engine under a load again and check for misfires and voltage drop. The battery is new so if there is a higher then normal voltage drop under load the alternator would be suspect as mentioned.



A note on the original rockers, they were not making any noise/tapping, when I checked them I found no play in the bearings. I finger rolled the bearings and they were smooth, until I tipped the rocker a bit and found a slight bit of drag. It can be easily missed so I just wanted to pass that along.
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Old 10-09-2019, 01:13 PM
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Did some light wheeling last Saturday and by Sunday the engine light is back on with p300, p301, and p305 codes. I checked the voltage while off road and found a steady 14v.

Today the engine light went out and is running fine.

I can now turn the engine light off (road driving for a couple days) or on (putting the tcase in 4wdr or winching).
Seems the engine light comes on when the rpms are around 700-800.

I plan to do a compression test tonight and a vacuum test at 700-800rpms.
I don't thing its a weak valve springs but the vac test will tell.

I also believe the compression test will be good as was my leakdown test however, I've seen other times when they differ.

Whatever the problem is I believe its isolated to the right head, maybe a cam phaser? or a solenoid that sticks?
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Old 10-09-2019, 03:55 PM   #24
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I'm interested to see what you find. It seems like you've hit all the obvious things to attack. Have you hooked up a real-time scanner to watch what's happening when the misfires actually occur?
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Old 10-09-2019, 06:06 PM   #25
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Sacj5, seems you are really focusing on the mechanical and neglecting the electrical side of the engine. Things like injector control, coil control, vvt system. This could be just a coil wire that is frayed and opening. Hard to diag without scan tool and really a scope.
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Old 10-10-2019, 12:20 PM
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Electrical side of the engine I've checked/replaced

Quote:
Originally Posted by SACJ5 View Post
Repairs and checks:
Swapped coils (no change)
Checked wire harness connectors and wires to the coils (twice)
New spark plugs
New right bank cam sensor
New o2 sensor
In my previous post I mentioned a compression problem is doubtful however, it is something I don't want to skip over especially when the dealership found two different results on the left head between a leakdown test and a compression test. Likewise with the vacuum test where I found a steady 19", this go around I'll run the test at 700-800rpms under load. Again, I don't think its a weak valve spring just want to confirm its not.

I understand this problem is hard to diagnose without a scan tool and scope, but I've also read page after page on this forum where the dealerships can't find the problem while using the scan tool (doesn't make me feel confident going to them).

Eventually I may have it scanned, but I want to rule out as much as possible and take a good shot at repairing this myself. I went from a intermittent problem and a engine light that went on whenever, to a controlled problem where the engine light will only go on under specific condition.

I welcome any advice I haven't tried already.
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Old 10-10-2019, 12:36 PM
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I'm interested to see what you find. It seems like you've hit all the obvious things to attack. Have you hooked up a real-time scanner to watch what's happening when the misfires actually occur?
It will not show live misfires, it will show some sensor values, just not sure what the ok range is for those sensors. While offroading I did check voltage and found 14v. It was thought I may have a low alternator output.

I've been bust so the compression/vacuum test will get done this Saturday.
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Old 10-12-2019, 11:48 AM
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Before the tests this morning the engine is running good, no codes with 2 misfires on cylinder 5

The compression test is good as expected #1-170, #3-165, #5-170

Vacuum is steady at 19" at 670-685 rpm, ran a test for exhaust blockage (cat) all is clear and working as it should.
I found the vacuum at 18" with the lights, fan-high, and brake lights on, idle stayed at 670-685 rpms, 11.8 TPS
Same as above with AC/fan high on 16" 680-690 rpm, 12.8 TPS
Battery voltage is 14v with lights, fan-high, and AC on or off.

Using winch at idle 12.7v idle didn't drop significantly

Before test I found 2 misfires on cylinder 5, after test I found 500 misfires on cylinder 5.

Took a short slow ride in 4wdr and found the misfires going down after restart, which means since the winch test there were no more misfires.
Took it for another ride (2 wheel dr) the engine is now idling rough with a pending multiple misfire. Misfires on cyl 3 (40) and cyl 5 (300s).

I suspect the more I drive on-road the misfires will go down.
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Old 10-14-2019, 07:38 AM   #29
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Looks to me like the alternator can't handle the winch load and supply required spark voltage at the same time.

Rough running is most likely from computer trying to adjust fuel trims and/or timing to try and eliminate the problem.

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