CEL - Cylinder Misfire

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Bermuda2012

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Hi Everyone!

I have got a Jeep Liberty 2007 with about 150k mileages some months ago, and the CEL was on. The code was initially P0306 (Cylinder 6 Misfire Detected), and it has been on at least since 2020 as I saw that on an old emission inspection certificate. After some while, another code came up, P0300 (Multiple/Random Cylinder Misfire Detected), so I decided to do something to fix the problem.

I got 6 new NGK Spark Plugs (ZFR6F11G/6987) and 6 new Mopar Ignition Coils (UF270 56028138) from eBay last month, then the mechanic guy replaced all of them together and also changed the spark plug gap to be 0.040 inches. Then he erased both codes and we expected everything to be perfect after that.

After driving some milages the CEL went back on again, and now after about 50 miles of driving it is still on. I thought the next thing might be the Fuel Injector so I wanted to change at least the fuel injector number 6 (even though the Mopar is very expensive, but I think it is the OEM), but another guy in AutoNation Jeep told me recently that the issue is less possible to be the fuel injector as it has a specific code called P0206. It has really made me mad and I have no idea what the main problem could be. It might not be very serious, but I would like to fix it and drive this Jeep at least for three more years.

So, I just wanted to ask here if anybody has experienced anything similar, or if anyone has any idea or suggestion that I should do next. I have searched a lot, but not sure what would be the best and cheapest thing to do next, like cleaning the throttle body and vacuum tube, changing the fuel injector number 6, doing a pressure or leak test, or whatever. I highly appreciate all your help buddies. Thanks so much in advance!
 

lfhoward

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I know this sounds simple, but I would run a few tanks of Shell V-Power gasoline or add injector cleaner like Techron or Seafoam to a few tanks. It will dissolve any crud in the injector and upper cylinder and may make it run smoother. But, if you have a mechanical problem like a head gasket leak, they won’t help. Do you lose coolant slowly over time from the radiator?
 

Ksat

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Get a capable scanner, look under Mode 6 and check the misfire counters for each cylinder. If there is a high count on just one cylinder, narrow your diagnoses to that cylinder. If there are misfires on multiple cylinders, you may have a lean condition on one bank (or both). Check fuel trims at idle when engine is warm, as well.
 

Bermuda2012

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I know this sounds simple, but I would run a few tanks of Shell V-Power gasoline or add injector cleaner like Techron or Seafoam to a few tanks. It will dissolve any crud in the injector and upper cylinder and may make it run smoother. But, if you have a mechanical problem like a head gasket leak, they won’t help. Do you lose coolant slowly over time from the radiator?
Thank you! That makes sense. I'll go ahead and run two full tanks of Shell V-Power Nitro Premium gas, and will add 20oz Techron fuel system cleaner to the first tank. For the second tank, I'll add 12oz SeaFoam spray to the intake part before the throttle body. Hopefully, it cleans the dirts and deposits in the cylinder, and clear the codes.

And no it doesn't lose coolant significantly over time, actually I've been using this car only for some months, but I will replace the coolant with Mopar antifreeze and fill up the reservoir at the next oil change service. (By the way, which oil is recommended for the engine? User manual just said API Certified SAE 5W-20 oils. I think Mopar or Mobil1 could be good.)

Also, if after these works the CEL was still on, what would you think I should do next? Replacing anything like the Gasket Head, the MAP Sensor, Fuel Injector #6, or all four O2 Sensors? I hope I don't have to spend so much money in this way!
 

Bermuda2012

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Get a capable scanner, look under Mode 6 and check the misfire counters for each cylinder. If there is a high count on just one cylinder, narrow your diagnoses to that cylinder. If there are misfires on multiple cylinders, you may have a lean condition on one bank (or both). Check fuel trims at idle when engine is warm, as well.
Thanks! Yeah, I'll ask the mechanic guy to do that the next time I see him. Although the lean air/fuel ratios can also come up with specific codes, like P0171 and P0174, it is still possible that something is wrong with one of the sensors for this cylinder misfire case. Which sensors do you think are more probable? Also, would it be possible to identify any leakage (if any) from the cylinders or valves by just doing the Mode 6 test, or that would need the Compression test?!
 

Bermuda2012

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Lifters ticking?
Well, I checked the engine sounds at idle, and I didn't hear anything weird like a continuous clicking or noise. The only thing is that after replacing all the Spark Plugs and Ignition Coils with the OEM parts about a month ago, I felt the Jeep vibrates a little bit on idle and when I drive it gets smooth, but maybe that was only my imagination.
 

MsRandiCook

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Well, I checked the engine sounds at idle, and I didn't hear anything weird like a continuous clicking or noise. The only thing is that after replacing all the Spark Plugs and Ignition Coils with the OEM parts about a month ago, I felt the Jeep vibrates a little bit on idle and when I drive it gets smooth, but maybe that was only my imagination.
I like where @Ksat is going. Get the timing checked. Really take some time and look at the electrical ground points. Make sure they are clean and tight.

Cam sensors are cheap and easy to change. For less than $20.00 install a new one.


A friend who owns a 2007 Nitro had close what you are describing and his was a partially plugged catalytic converter.

Wish I was more help!
 

budget76

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ONE: DO not change coolant. You do NOT have a coolant issue, so leave it alone for the time being. Fewer variables better.
TWO: Yes, get a scanner to determine if dirty/fouled injector, or what. Rule out things.
Yes I too have thrown cheap parts in, but they may be bad and you aggravate the issue.
Could be 1 cylinder, or whole bank, or other. need diagnose, but i understand your frustration not having been down this road.
No harm in injector cleaner, but again no proof it is injector issue. no harm.
Concerned OEM plugs and or colis from ebay. Often they are fake oem even though we hope not.
good luck.
 

GomelBY

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Need help guys! Bought 2003 Liberty about 2 years ago, right after purchasing replaced all 6 spark plugs and 6 coils. 7 months ago had misfire in cylinder 6, changed spark plug and coil for that cylinder. Today went to start a car, a lot of vibration and shaking on idling, check engine is blinking. I have dissent 800$ scanner, getting misfire in cylinder 6 again. Any ideas? Spark plug and coil, that’s not the original problem, something else is cousin them to go bad. On the way home yesterday, it was dark, while driving, all electrical (lights) died for about 1 second, then came back on, and today this happened. Any ideas?
 
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ltd02

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My 02 did that lights out thing a couple times. I wound up replacing the battery. It was an old battery and these things are pretty sensitive to any voltage drop. Is it charging ok? I also had a blinking #6 misfire at one point but my coolant reservoir had dripped on it.
 

dtennes

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Need help guys! Bought 2003 Liberty about 2 years ago, right after purchasing replaced all 6 spark plugs and 6 coils. 7 months ago had misfire in cylinder 6, changed spark plug and coil for that cylinder. Today went to start a car, a lot of vibration and shaking on idling, check engine is blinking. I have dissent 800$ scanner, getting misfire in cylinder 6 again. Any ideas? Spark plug and coil, that’s not the original problem, something else is cousin them to go bad. On the way home yesterday, it was dark, while driving, all electrical (lights) died for about 1 second, then came back on, and today this happened. Any ideas?
I am going through a 2003 3.7L overhaul, and I am plagued by a cyl 4 misfire. Ping me directly through this forum and we can start a dialogue about experience to date.

Meanwhile use your scanner to review "Freeze Frame" info (state of the vehicle when the MIL triggered) and record it all. Use the scanner to reset the ECU, set your trip odo to 0.0. Drive until the MIL p;ops again, repeat logging and reset activities. Do that 3-4 times so you have a point of reference regarding the consistent state of the engine at MIL trigger. Then you can start narrowing the root cause.
 

dtennes

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Hi Everyone!

I have got a Jeep Liberty 2007 with about 150k mileages some months ago, and the CEL was on. The code was initially P0306 (Cylinder 6 Misfire Detected), and it has been on at least since 2020 as I saw that on an old emission inspection certificate. After some while, another code came up, P0300 (Multiple/Random Cylinder Misfire Detected), so I decided to do something to fix the problem.

I got 6 new NGK Spark Plugs (ZFR6F11G/6987) and 6 new Mopar Ignition Coils (UF270 56028138) from eBay last month, then the mechanic guy replaced all of them together and also changed the spark plug gap to be 0.040 inches. Then he erased both codes and we expected everything to be perfect after that.

After driving some milages the CEL went back on again, and now after about 50 miles of driving it is still on. I thought the next thing might be the Fuel Injector so I wanted to change at least the fuel injector number 6 (even though the Mopar is very expensive, but I think it is the OEM), but another guy in AutoNation Jeep told me recently that the issue is less possible to be the fuel injector as it has a specific code called P0206. It has really made me mad and I have no idea what the main problem could be. It might not be very serious, but I would like to fix it and drive this Jeep at least for three more years.

So, I just wanted to ask here if anybody has experienced anything similar, or if anyone has any idea or suggestion that I should do next. I have searched a lot, but not sure what would be the best and cheapest thing to do next, like cleaning the throttle body and vacuum tube, changing the fuel injector number 6, doing a pressure or leak test, or whatever. I highly appreciate all your help buddies. Thanks so much in advance!
I am going through a 2003 3.7L overhaul, and I am plagued by a cyl 4 misfire. Ping me directly through this forum and we can start a dialogue about experience to date.

Meanwhile use your scanner to review "Freeze Frame" info (state of the vehicle when the MIL triggered) and record it all. Use the scanner to reset the ECU, set your trip odo to 0.0. Drive until the MIL p;ops again, repeat logging and reset activities. Do that 3-4 times so you have a point of reference regarding the consistent state of the engine at MIL trigger. Then you can start narrowing the root cause.
 

Trainmaster

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I had a permanent #4 miss P0304 and Coil Secondary Failure P0354. Switched plug and coil to another place and codes and miss remained on #4. Coil had been wet from leaking coolant earlier. Checked the wires from the coil.

One lead is hot with ignition on, the other is pulsed ground from the computer. The ground pulsing wasn't there on #4 but was present on other cylinders.

Replaced the computer with a programmed one (VIN and mileage must be programmed by seller) from ebay ($129 for a 2005) and the problems vanished.

Apparently the #4 driver in the computer, a silicone controlled rectifier, dies when suffering a short for awhile.
 

dtennes

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I had a permanent #4 miss P0304 and Coil Secondary Failure P0354. Switched plug and coil to another place and codes and miss remained on #4. Coil had been wet from leaking coolant earlier. Checked the wires from the coil.

One lead is hot with ignition on, the other is pulsed ground from the computer. The ground pulsing wasn't there on #4 but was present on other cylinders.

Replaced the computer with a programmed one (VIN and mileage must be programmed by seller) from ebay ($129 for a 2005) and the problems vanished.

Apparently the #4 driver in the computer, a silicone controlled rectifier, dies when suffering a short for awhile.
Swapping in a brand new PCM from Flagship didn't work for me unfortunately. In my case I think it was cumulative wear and tear from 305K mileage. Had corroded wire insulation, plus dying injectors, coils MAP, TPS, and a mixed bag of unreliable chinese junk parts installed by various local garages.

I recently posted an "engine replacement checklist" that goes over pretty much everything you have to do to ensure a reliable 2003 (also applicable to 2002 and 2004) 3.7L v6 engine swap. Hope that helps others in this sort of effort.
 

Trainmaster

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If you checked the two wires feeding the coil for continuity and grounds, and you had no other codes, and the new computer worked, you should have been fine.

When replacing the PCM in these Jeeps you need the *exact* part number of the original (except for the two-letter date code). Lots of the suppliers sell any junk that plugs in and it simply doesn't work.

The problem with throwing a bunch of parts at a problem is that half the Chinese crap you buy today doesn't work. Then you are fighting with multiple failures. It's unlikely that more than one part fails at a time. Go after the problem, get it running and then take it from there.
 
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