I have been having misfire issues that I for the life of me can't seem to pin down. These misfires started about a month ago and everything I have done has failed to fix it.

I will get a misfire on cylinder 1 only during deceleration some of the time. It isnt constant and so far I have not found any specific trigger that causes it to happen. I will get the blinking check engine light and the code will be misfire on cylinder 1. The truck will run just fine during and after the blinking check engine light so clearly the misfire isn't a major one.

Every once in a while though the misfire will be bad enough to throw it into limp home mode, and I will get codes 300, 301 and 306. This is multiple misfires on 1 and 6. These have been the only symptoms that I have found so far.

To date I have done the following to see If I could figure out what is causing it.

~Change Spark Plugs
~Check Spark Plugs after the swap, Cylinder one plug is burnt on one side, all other plugs are good.
~Changed coil pack to a coil pack that came off a perfectly running vehicle.
~Seafoam
~Swapped Injectors around, misfire did not follow the swapped injectors
~Compression Test- Perfect compression
Cyl 1-150
Cyl 2-140
Cyl 3-150
Cyl 4-150
Cyl 5-150
Cyl 6-160
~Brand new MOPAR TPS
~I even bypassed the wiring harness for Coil Driver #1 to try an rule out a short to the coil rail

Nothing have worked, or affected it at all.

I really think that this is a electrical issue due to the inconstancy that it occurs, but I just can;t think of what would be causing this issue. I am hoping somebody may have dealt with something like this before and can give some advice on what to do next.

 

Any suggestions or ideas to start on guys?

 

"burnt on one side" is a sign. I'd start looking for vacuum leaks and run water through the intake or Mopar Combustion Chamber Cleaner.

What plugs did you install?

 

You may want to check your fuel pressure at the fuel rail with the engine idling, throttle advanced, then return to idle. Pressure should be consistant 49 +/- 5 psi.

You can (refundable deposit) rent a fuel pressure test set from your nearby auto parts store.

If the fuel pressure is okay then I would test the MAP sensor.

Let us know how you make out with the fuel pressure.

 

I was incorrect, It was't seafoam that I ran through it I did use the Mopar Combustion Cleaner.

I replaced the plugs with Champion Coppers, the exact ones listed on the firewall.

I will start looking into the fuel pressure issue, I'm assuming there is a proccedure for testing the MAP sensor Ill have to look that up and get going on that.

Thanks guys, I really am stuck on this issue and I need to find a fix with this being my daily.

 

Update:

Tested fuel pressure today, not looking good.

At idle the gauge was all over the place, from 55psi all the way down to 35psi

Held a strong 51psi under load

But reving up to 2500, let off till 1500 and then getting back on it again saw the pressure drop to 35psi.

Sounds like I have a bad fuel pump that could be causing lack of fuel thus creating a misfire.

 

Update-

Replaced the fuel pump today, and so far so good. I have been trying to recreate the misfire situation and no luck so far. The fuel filter was literally black, im guessing that played a part in this issue.

Hopefully this fixes it, but if not Ill post up again. I figured id at least post what worked for me just in case anybody else gets these symptoms.

 

Thanks for the update.

Just wondering why a subpar fuel pressure would cause a cylinder misfire in only cylinder #1 (and later also cylinder #6)....is this a 'special' cylinder, since I've been reading quite a few times about codes relating to cylinder #1?

 

Well sadly the fuel pump didn't fix the problem so only thing left to do is check the wiring connection for injector 1 to the computer and if that checks out than at least I can completely rule out fuel and ignition at this point.

My theory is that it is something to do with cylinder 1 thats causing the misfire and when it misfire bad enough it throws off cylinder 6 and causes that to misfire also. Because 1 and 6 fire at the same time if one is off bad enough it can throw the other cylinder off ive confirmed that with dealer techs.

At this point while it could possibly be a sensor more than likely it is something to do with the valvetrain for cylinder 1. Could be a lifter, valve seal, valve spring. What really sucks is that ill have to pull the head if its a lifter or bad valve.

 

Did you recheck fuel pressures with after the pump swap?

 

No I didn't, Id have to borrow my buddies gauge again. Next step is my dealer tech friend is going to bring home the dealership computer one night and we are going to go through the live data and see if anything jumps out at us sensor wise, or a bigger indication of a potential burnt valve.

 

Check that fuel pressure to make sure that is now ok...

 

Update- finally installed a new mopar MAP sensor, no luck.

Though I'm almost positive this is a sensor issue. I reset the computer yesterday after installing and it drove perfect for 40 miles. I tried several times to get it to throw the code during those 40 miles and no luck.

I'm guessing that after the data is clear its taking time to get bad data from a sensor and throw it off.

Only question is what sensors other than tps and map would have the potential to be causing this misfire?

 

Thought I would just get this one closed up so if anybody else has this issue they will know what to do.

The issue ended up being the camshaft synchronizer, the teeth on the gear had worn down bad enough that it was very off timing wise.

Apparently this is an issue with the design, and my friend at the jeep dealership said this happens all the time and that the 2005 wrangler 4.0s actually had a recall related to it. I had another one put in and timed it using the dealership computer and she was good to go.