Misfiring is back again on 2004 TJ

[Inky]

Had a P0304 problem and changed ignition coil rail and plugs now it’s back as p0302, but I noticed it only happens when running after 50 miles, so when warm. Engine seems hot but not hot on thermal gauge on the dash. When vehicle starts from cold it runs great. What’s next fuel injectors?

 

[CharlesHS]

I would perform a Combustion Chamber cleaning with Mopar Combustion Chamber Cleaner or Sea Foam.
When I purchased my '01 Sport 4.0L I received numerous random misfires even after replacing the spark plugs.
I performed a CC cleaning with Mopar CC cleaner and had quite a plume of dark exhaust coming from the tail pipe.
The misfires were due to carbon build up in the Combustion Chambers and all the chemical additives that were in the California gas.
Since moving to Florida and periodically adding the Hi Mileage Sea Foam fuel system cleaner to the gas tank; the misfires have remained gone.

 

[Inky]

I would perform a Combustion Chamber cleaning with Mopar Combustion Chamber Cleaner or Sea Foam.
When I purchased my '01 Sport 4.0L I received numerous random misfires even after replacing the spark plugs.
I performed a CC cleaning with Mopar CC cleaner and had quite a plume of dark exhaust coming from the tail pipe.
The misfires were due to carbon build up in the Combustion Chambers and all the chemical additives that were in the California gas.
Since moving to Florida and periodically adding the Hi Mileage Sea Foam fuel system cleaner to the gas tank; the misfires have remained gone.

Thanks Charles. Will give it a try. How long did it take for the sea foam to work? Thanks again.

 

[Jerry Bransford]

Thanks Charles. Will give it a try. How long did it take for the sea foam to work? Thanks again.

Mopar's CCC is 99% water and 1% ammonia as a detergent. You can do the same with plain old ordinary tap water. Yes that is absolutely true.

Fill a soda can with water then start the engine. With the engine idling, SLOWLY (!!!) trickle the water into the throttle body. It should take a couple minutes to empty the can of water. Don't dump the water in too fast, that can cause bad problems for the engine. I suggest the soda can because it holds the right amount of water and it's easily controlled so you don't accidentally dump too much in at once.

The water is highly (!) effective at getting rid of carbon deposits. This was discovered during WWII by engine mechanics. Water injection was added to bomber engines to give them more power so they could take off more easily and cruise at higher altitudes with heavy bomb loads. The engine mechanics were happy at how clean the engines became with the water injection. Which by the way is still used today in some engines.

 

[ejay]

I had a similar misfire on my 04 and ended up (I think) tracking it down to an intermittent wiring harness issue. I pulled the harness, moved every bend and kink, and reseated everything with dielectric grease and the problem disappeared. This was after changing all injectors, testing coilpacks, and testing every plug and plug wire. I even went through and tested every point related to ignition at the ECU and that where I found signal degradation but not everytime I tested. It was strange.

Anyway, the problem hasn't returned.

 

[CharlesHS]

Mopar's CCC is 99% water and 1% ammonia as a detergent. You can do the same with plain old ordinary tap water. Yes that is absolutely true.

Fill a soda can with water then start the engine. With the engine idling, SLOWLY (!!!) trickle the water into the throttle body. It should take a couple minutes to empty the can of water. Don't dump the water in too fast, that can cause bad problems for the engine. I suggest the soda can because it holds the right amount of water and it's easily controlled so you don't accidentally dump too much in at once.

The water is highly (!) effective at getting rid of carbon deposits. This was discovered during WWII by engine mechanics. Water injection was added to bomber engines to give them more power so they could take off more easily and cruise at higher altitudes with heavy bomb loads. The engine mechanics were happy at how clean the engines became with the water injection. Which by the way is still used today in some engines.

JB,

What you are describing is the Commifornia friendly Mopar CCC, but the other states "good stuff" Mopar CCC is more concentrated with chemicals that are no longer allowed in Commifornia which cleans the TB and CC better. While in Commifornia I sourced the good stuff from a friend that is a Mopar technician.

 

[Inky]

Thanks everyone. Much appreciated

 

[pagrey]

Just curios, what spark plugs did you choose? The type is very important and you mentioned just replacing them.

 

[Inky]

Just curios, what spark plugs did you choose? The type is very important and you mentioned just replacing them.

Champion 7034 Double Platinum

 

[CharlesHS]

Champion 7034 Double Platinum

When I tried those in my ‘01 4.0L my Jeep had numerous misfires. When I replaced them with the NGKs the engine ran properly.

 

[pagrey]

I have good luck with the stock NGK plugs too, these things seem to be pretty picky and plugs are cheap. I thought those were okay but if what @Jerry Bransford suggested doesn't work maybe you could try the other plugs. Besides the water thing is probably fun, especially if your neighbors are watching.

 

[Inky]

When I tried those in my ‘01 4.0L my Jeep had numerous misfires. When I replaced them with the NGKs the engine ran properly.

Wow. Ok. I guess I need to get new plugs as well.

 

[Inky]

My misfires get worse though as the engine warms up and after roughly 50 miles each time. Is that the pattern with plugs? They run fine up to 50 miles

 

[Jerry Bransford]

Champion 7034 Double Platinum

Champion's 3034 (edited, see below) is actually a single-tipped platinum design that is well known to cause misfires in the newer distributorless 4.0 engine with the coil rail. Autolite's AP-985 has the same problem with the newer 4.0.

Edit: My memory on the 7034 was/is faulty. That is indeed a double-tipped platinum plug, I was thinking of the 3034. My apologies for having fucked that up.

For double-tipped platinum plugs that work well with the newer distributorless 4.0, the Champion 7412 and the Autolite APP-985 both work well and are good for 100k miles. Or the iridium tipped Autolite XP985 which is what I run and is good for closer to 200k miles.

 

[Jerry Bransford]

JB,

What you are describing is the Commifornia friendly Mopar CCC, but the other states "good stuff" Mopar CCC is more concentrated with chemicals that are no longer allowed in Commifornia which cleans the TB and CC better. While in Commifornia I sourced the good stuff from a friend that is a Mopar technician.

Plain water works perfectly well for this job. It really does.

 

[Jerry Bransford]

... Besides the water thing is probably fun, especially if your neighbors are watching.

It won't smoke while using the recommended water.

 

[pagrey]

I blew a head gasket in my 1979 Honda Accord about a million years ago and pulled into a gas station to fill up. I filled the entire area under the cover with thick steam like tule fog and a lady went running out screaming with her hands in the air thinking the station was about to blow. I'll never forget that, probably what I was visualizing with the water. I've never done the can thing, probably obvious at this point.

 

[Jezza]

Do a compression and leakdown test.

 

[CharlesHS]

Plain water works perfectly well for this job. It really does.

I have heard of spraying a mist of water into the TB for CC cleaning; just haven't tried it.
Thanks for the information.....

 

[williambmac]

I have heard of spraying a mist of water into the TB for CC cleaning; just haven't tried it.
Thanks for the information.....

It's an old school mechanics trick for cleaning the top end. It works really well on older engines, not so much on newer direct port injection engines.