I have an 03 Grand Cherokee, 4.0L Engine. 98,000 kms (60,000 miles) One really cold night (-30 degrees celcius) I started it up and it was misfiring. It had always been plugged in and regular maintenance done.

Ran the code, it was P0303 - #3 Cylinder Misfire. I read every stinkin forum post I possibly could find on every jeep website, and started doing all the recommended ideas. I read all the TSB's on this issue too. Including a trip to the Dealer and tried all of their ideas.

They said the injector was faulty and to replace it. Also change the plugs to the original Champion plugs, because I had bosch platinums in it. I did and after this and everything else i've tried, They're completely stumped. They have had it in on two separate full days and are now calling their tech support because they have no idea how to fix it.

Here's whats been done:

New spark plugs (twice, with the bosch in you can actually drive it. With the champions it chugs so hard you have to pull over)

New Fuel Filter
New fuel injector on cyl. 3
New Oil/filter change
Sleeves on all six injectors
Thermostat recently changed
Rear main seal done 1 year ago
Coil Pack Rail looks good, boots and coils inside them look new
Fuel pump tested and checks out fine
Battery tested and checks out fine
Combustion cleaner through throttle body
Even tried the Seafoam treatment

So It seems like the third plug is getting lots of fuel. The electrode looks green like fuel and smells of gas. The other plugs are black and 5 & 6 are a bit oily. My senior ford tech friend says that with all of that done to it and judging by all the carbon coming out of the exhaust and and the putt-putt exhaust, that it is likely a burnt valve/ring. I have read the TSB's about the valve rotation and I am starting to believe that it needs a valve job.

The only thing is that it should be covered under the powertrain warranty and the Dealer won't fix it because they still don't think that is the problem. Warranty is almost up, and they refuse to open it and check the valves. They are supposed to talk to their tech support this week, and the jeep will go back in next wed. I even made the service advisor read the TSB's.

I'll pull the head off myself if I knew that was the problem. What do you guys figure? Has anyone resolved their misfire? So many of these with the same problem. I think it's time Chrysler made it a recall. Class action suit is needed!

thoughts?

 

WTF??

https://www.cherokeeforum.com/f5/rep...se-read-32720/

 

Have you done a compression check?

Found my mis-fire that way. Worn cam and lifter. Lifter had a hole worn in it.

Jeff

 

well, i havent had that problem with my ZJ (knock on wood) but on my 1993 mustang, i had the same exact problem, i changed plugs, fuel filter, air filter, coil pack, wires, and it wouldnt go away, so my friend suggested taking off the egr valve, i took it off, shook it, put it back on, and the car ran mint....i know it wasnt a jeep, but its something you can look into, good luck

 

I had a problem that we just resolved yesterday. Distributor plate was bad. Take out your distributor and see if you can hold the gear at the bottom and make sure the plate where the rotor sits can't move at all. Mine was moving. Replaced the rotor and now it runs like a champ! Maybe something to check. I'm not an expert.

 

I have a problem like this as well but for me its a misfire in #4, has new inj. plugs and coil pack, compression tested all cylinders #4 is at 170lbs all others are at the 150 to 160lbs area. I was going to pull the valve cover off and check springs, am I on the right track? what if anything am I missing?

01 Cherokee sport, auto 4.0 118K miles. check engine light is on AND flashing (indicates MAJOR misfire) I am not driving it at moment.

 

No distributer.....coil packs

 

time to do a compression test and a leak-down to check the mechanical condition of the engine. if there is a burnt valve, it will show up in those tests.

underconstruction, if you have higher than normal compression in a cylinder, it usually means that the exhaust is restricted. since it is only on one cylinder, that leads me to think either the lifter is collapsed or the cam is flat. i would pull the valve cover, rotate the engine and check to see that #4 exhaust valve is opening the same as the rest.

zedpapa

 

Have you not replaced the cam and crank sensors? These are notorious for problems with Cam and crank sensors causing no starts, misfires, and low power. If crank sensor came loose or is improperly adjusted the ecm won't know when to throw spark to which cylinder.

 

My opinion? Replace the coil pack. It could be shorted internally at cylinder #3. The green color (copper sulfate) tells me it's not firing AT ALL! #3 & #4 fire together every revolution. It's called "waste spark" where the plugs fire at the top of the exhaust as well. SO, you have #4 going out intermittently as well. That's what's causing the violent shake. I've found the best service with NGK ZFR5N plugs. I believe that's what's recommended after 02 anyway. The coil pack uses 3 coils to fire 6 plugs. The usual problem is with #1 & #6 because there is long connector to #6 that leads all the way to coil #1.

A good new coil pack costs about $70 on rockauto.com or even try a junkyard pack!

 

Anyone happen to notice this is an 8.6 year old thread? Lol.....

 

Nope, went right by me. Okay.......

 

One thing is for sure, we'll never know how it turned out.......

 

I did.

 

lol