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P0306 Cylinder #6 misfire?

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29K views 44 replies 11 participants last post by  RCS1300  
#1 ·
I sold my WK yesterday. The new owner successfully drove the 700 miles home with no problems but today he experienced a flashing CEL followed by the engine dying. He pulled over on the side of the road and was unable to restart the Jeep. It'll turn over just fine but not start. He had it towed home and pulled the codes.

The first two I have had before and were known to the new owner beforehand.

U110A - Known issue with AEV/EGR module. Randomly loses communication with steering angle sensor.
P0420 - Catalytic inefficiency that I randomly would get

P0562 - Low voltage. It was slow to start after sitting for a month before selling. I'd assume that's what this is from
P0306 - Cyl 6 misfire... Going out on a limb that this is the culprit
B1634 - Left mirror short? Not sure on that one. I never noticed a problem with the mirrors.

The P0306 code is for a cylinder #6 misfire I believe. Has anyone experienced anything similar? It has been running fine for 6 years with a perfect maintenance record. I feel pretty bad that the new owner didn't even make it 2 days without an issue! Any help would be greatly appreciated. The new owner is also a member here so I'm sure he'll chime in.

Pic for clicks:

 
#2 ·
I will not have time to look into this until tomorrow. Basically after merging onto the highway, got up to about 75, I got what sounded almost like a bad lifter tick (my first thought was drive shaft contacting the skid, really almost sounded something like this, but I know this had been addressed on this rig). Is was just a short burst, initially thought it was the radio. Heard it again and killed the radio to notice it still there. I let off the gas (coasted) and it went away, accelerated and it came back. At that point the CEL started flashing and I decided to bail off the highway. Made it onto the off ramp and coming into the turn lane it just died completely. Time from flashing CEL to death, about 300 feet. After that it would not start, cranks over fine but would not fire. After sitting for maybe 30 minutes and a long crank I was able to get it to start for literally only a second before it died again. Had it towed back to the house at that point. I intend to pull the plugs out of cylinder 6 tomorrow and see what I can see.
 
#9 ·
Okay, cleared the DTC's, discharged that system and gave it a crank. Here is the result, did not generate any DTC's after this. I am going to take the battery in and have it tested.


Edit: Battery is fine, tested good. I ordered a NorthStar AGM just to have the right size in there (Optima is 34r) but that is not the issue. Did not have time today to look at anything else. Coil swap will be pointless as the motor will not even start. Best I can do is pull the plugs and see how they look.
 
#10 ·
If it does that much it's not your battery or your starter. Seems like what my 99 was doing when i needed a crankshaft position sensor...
 
#12 ·
The engine is turning over just fine so its probably something simple keeping it from starting. It almost has to be fuel/air/or spark related. The fuel and air should be easy:

For fuel, there are 2 filters (that are unfortunately "non-serviceable") located in the tank that could definitely have gotten clogged up with bad gas or even ice if there happen to be some water in the tank. That or possibly a bad fuel pump? Its hard to hear so have someone else turn the key to the start position. You should hear it run momentarily.

Air is obvious. The K&N was pretty clean but you could try taking the cone off to start.

Spark is the more difficult one. It could be ignition related or a random sensor. I'd say pull a plug, ground it, and see if it sparks. But unfortunately its not that simple on the WK. From WKjeeps:

The 5.7L V-8 engine is equipped with 16 spark plugs. Two plugs are used for each cylinder. The 5.7L is also equipped with 8 separate and independent ignition coils. The one-piece coil bolts directly to the cylinder head cover and attaches the coils secondary output terminal directly to a spark plug using a rubber boot seal. A separate primary electrical connector is used for each coil.

Two knock sensors (one for each cylinder bank) are used to help control spark knock.

The 5.7L engine does not use a conventional distributor.

The ignition system consists of:

16 Spark Plugs (2 per cylinder)
8 Separate, Dual-Secondary Output, Ignition Coils
2 Knock Sensors
Powertrain Control Module (PCM)
Also to be considered part of the ignition system are certain inputs from the Crankshaft Position, Camshaft Position, Throttle Position, 2 knock and MAP Sensors.

It could possibly be a bad coil but you'd think it would still start with the other 7. I could be wrong though. You could also try using the Flashpac and returning it to the stock tune. I haven't heard of anyone experiencing problems with the 91 octane tune but it may be worth trying.

Honestly though, it sounds fuel related to me. It seems to start but barely runs like its being starved for fuel. Do you have anywhere warm you could park it overnight to see if you did possibly get some bad gas contaminated with water?

I hope you have some good luck here. Keep me updated.
 
#13 ·
The engine turns so that is excellent. Does sound starved of fuel. Have someone turn the key to accessory on and put your ear close to the fuel pump to see the fuel pump starts. It will make a whirling sound like a very small electric motor the size of a salt shaker. If the fuel pump does not start after several attempts I would check the relay and/or fuse for the pump first.
 
#14 ·
Okay, finally had a chance to play with it more. It has been snowing and in the mid teens for the past week.

I put in a new battery, which I had already ruled out. However, I wanted the correct size, as the 34R was not very secure in the tray. My NorthStar showed up damaged from QT and they are out of stock with the manufacturer for at least two weeks. So I just picked up an Autocraft Platinum AGM. I replaced both terminals, the negative was in poor shape.

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After that I put in new cam and crank position sensors. They are cheap enough and a bad crank, which is a common failure on these, could cause my no start issue. Unfortunately that was not it. I am pretty settled on it being a fuel issue at this point. Now the pump is priming, the reason I was unsure initially is because the pump does not prime as my '04 WJ does. The pump actually primes when you unlock the Jeep via the remote. This is definitely a much better design as most people do no let their pump prime when they get in the vehicle, they just turn it full over. I normally hit the remote a good distance away from the rig. But I happened to be standing right next to is today while unlocking and I heard it prime. Just to confirm I locked it, crawled under and unlocked it, and it definitely kicks on.

Now the reason I think fuel is when I turned it over I gave it a little gas and actually got it to start. As soon as I let off it died. So I did it again and this time kept feathering the gas and it stayed running, but every time I let off it would want to die. I ran it this way long enough for my flashing CEL to come back (maybe 20 seconds) and turned it off immediately. Pulled the code and got P0300, multiple cylinder misfire. Unfortunately the 5.7 does not have a Schrader so I cannot hook up my gauge. Not sure where to go from here.
 
#15 ·
This is where you need to do some diagnosis. I have a 4.7. With the 5.7 I believe you have to obtain a special adapter (miller tool #6539 or 6631) to tap into the fuel line and test the fuel pressure. Before I did that I would probably switch the fuel pump relay with another similar relay to see if you have a faulty relay.

Assuming your vehicle is a 2010 so unless it is high miles the fuel pump should be okay I would think.
 
#19 ·
There may be an easier way to test for a fuel problem than to check fuel pressure. Please check with an expert first to confirm but you may be able to spray a starter fuel into the air intake and then try to start the jeep to see if it runs for a longer period of time. This is dangerous and I have never done it. You could otherwise check the fuel pressure.
 
#20 ·
There may be water in your gas tank. If your last gas stop occurred during or after a tanker was filling the gas station underground tanks, you could have pumped water into your gas tank. Since water is heavier than gas it sinks to the bottom of the tank right where the fuel pump gathers fuel.

When a tanker fills underground gas tanks it churns up any water in those tanks. It takes some time for that water to settle back to the bottom of the underground tank. If you pumped from these tanks before the water settled you may have water in the bottom of your gas tank.

Two options. Pump out your tank and put in a few gallons of fresh gas. Or, you could add sea foam to your gas and it will absorb a small amount of any water in the tank. Sea foam will only work if there is less than a cup or two of water in the tank. If more water than that you will have to siphon it out.
 
#21 ·
New development. Since I have to keep giving is gas to stay running there is only so much diagnostic work I can do. Had a buddy stop by who walked around it while running. I am dumping white smoke out of the exhaust, the exhaust is producing a lot of condensation. So much that it is dripping pretty good from the tail pipe and also before and after the muffler at the joints. Additionally, the coolant take is about empty. I had already checked the dipstick when this all started and the oil level is fine, no signs of coolant in there at all. My buddy thinks there is a possibility it could have a small leak between cylinders.

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#25 ·
It's typical for water vapor in the atmosphere to condense in a vehicles exhaust system. Especially one that has sat for a few weeks. Some of the water will evaporate as the exhaust heats up as white smoke and some will get forced out in liquid state. If it is coolant you will definitely smell antifreeze. It'll be pretty obvious. Even my new SRT spits out water and white smoke on initial startup on a cold morning. Also the coolant is where it was when I took the for sale pictures 2 months ago so I doubt there is a leak. I did not add to the coolant level.



I still think it sounds like you got some bad gas.
 
#24 ·
You may have a coolant leak somewhere. Not sure it is in the engine. If coolant were leaking into your engine it would be in the engine oil. Could be a leak in the radiator, a hose, a hose seal, the water pump gasket, etc. Not sure this is causing your non-running condition. You can pressure test the cooling system to try and find it.
 
#27 ·
I'm still not thinking bad gas, it still has over half a tank and had sat for 12 hours before it randomly died on the highway. I am familiar with typical water vapor in the exhaust, but this was excessive and not constant, it would puff out almost in rhythm. Almost like when it hit the wet cylinder it would burn that off and push it out.

At any rate, I had it towed to the dealer this morning. Not happy about it but it has been parked for two weeks and I can't just keep throwing parts at it. I have basically driven it one day since I've owned it. If it's just bad gas that would be fantastic.
 
#28 ·
too bad it all ready went to the dealer. I have seen this type of problem with bad gas on many cars. I made up a cheap system to suck fuel / water from the bottom of the tank. buy a cheap electric fuel pump at the auto parts store, attach about 3' of fuel line to the inlet side & 1' of clear vinyl hose to the out let side. feed the fuel line into the tank & the clear line into a can or gas jug. power it up & run until you get clear clean gas. that will get the moisture / water out of the tank. then try to restart the car. it will run rough until the lines & injectors clear out. good luck
 
#31 ·
I'm not sure if this engine has the similar to the CRD harness, but the harness from the ECM bus line runs under the battery tray on some of the other engine versions. This harness can rest on the a/c line going to the cooler under the battery tray. Then melt causing communication issues. I wrap mine in cool tape and zip tied it up to the battery tray. So you may want to look at or check the harness under the battery tray.