incurable misfire an 18 month saga

[bandofthHawk]

For a year now I chronically have a cylinder 4 misfire code. P0304. It started off with appearing once a couple of months or so but long story short its chronic now and its always on. If I delete it with my scanner it now comes right back the next day. I've tried everything. im not gonna pass inspection in May like this.
Did compression test everything checked out
New plugs tried both champion and ngks stock gap .035
Multiple coil packs (replaced same time as plugs)
Cam sensor is fine
New tps sensor
New IAC
New throttle body
New injectors tried set of 24# and 25# tried moving injectors around. still always cylinder 4 misfire
New 02 sensors
New exhaust manifold gasket and pre cats
Air intake is new filters clean
I don't believe i have a knock sensor
wouldn't thinks its the fuel pump
wouldn't think its crank sensor
Always runs under 210*
Never overheated
Oil changed every 3k
Oil pressure is good
leaks no oil
leaks no coolant
Starts up fine everyday no hesitation.
Has plenty of power still
I've concluded every time the code is triggered its when im parked with he engine running for more than 5-10 minutes or so. Seems to be caused by idle lope. I've tried resetting the battery. I've tried premium gas made no difference. I'm really at a loss here. only have about 30k on motor. id hate to have to get rid of the XJ with a great running engine if its just some computer related crap..i don't think a tune would compensate for a misfire problem..dunno

engine parts list
00' xj block bored.30 over
4.2 crank
4.2 rods
Comp xtreme 4x4 cam duration 250/258 *says not to be used with fuel injection according to Comp. but ive heard that comp is wrong about that.
Lift. 462/.485 hydraulic flat tappet cam
Crower camsaver lifters
Keith black silvolite pistons
62mm tb
24# injectors
Banks header
Ported head (older style head) not 0331
melling HV oil pump

any advice will be appreciated. you guys have informed me well before. I thought I had good progress but looks like I cant get out of the woods with oem problems

[SilverXJ]

Is there any indication of a misfire? Engine stumble or backfiring?

You have the comp cams 68-231-4. That should not cause an issue. You said you have an idle lope? With that cam you should have a pretty smooth idle.

[bandofthHawk]

My idle does feel rough and shaky. I was trying to listen to the motor running earlier today at idle and I believe I hear a valve tapping near the cylinder 4 area. Sounds like a clock ticking pretty fast.

[SilverXJ]

The idle with that cam should be pretty smooth.

Sounds like its an internal problem, especially since you hear a sound on only #4. Possibly a valve not closing or opening. The sound might be lash in the valve train. Pull the valve cover, rotate crank until both valves are completely closed on the compression stroke. Look for a lose rocker or pushrod. Could be soothing as simple as a bent pushrod, sticking lifter internally, bent rocker arm, or rocker bolt backed out. Could be slightly worse like a bent or stuck valve. You may also have to run the engine with the valve cover off to narrow the sound.

[bandofthHawk]

Right. From an electronic standpoint everything checks out. figured it has to be a mechanical problem. At idle it is definitely rough and you can see the needle on the tach hovering above and below 1k. A top end rebuild isn't the end of the world i suppose. I have a buddy with a shot 4.0 that sounds like marbles rolling around. I wouldn't think I'm at the level of complete engine failure . as i am always on top of routine maintenance. Actually the original owner of my jeep had the factory 4.0 fail at 120k. That's why he opted for the stroker build. I have a local shop that builds custom strokers. He's the guy who's helped me check everything so far as I'm no expert. If he pulls the valve cover and sees a bad rocker arm or spring for example how would he know precisely what specific parts would be the appropriate replacement? Just wondering. Thanks for the guidance

[Retlaw01XJ]

Possibly a valve not closing or opening.

Put a vacuum gauge on it. If there's a valve problem it should result in an erratic vacuum reading.
Here's a chart that shows the basics (first hit in a Google search... lots more out there):
http://www.earlycuda.org/tech/vacuum2.htm

Question: how does the ecm determine there was a misfire?

[bandofthHawk]

What is the likelihood that the lobes of the cam are worn off? If so would it be best to use the same comp cam or try something different if I had to replace the cam? The shop I've taken it too said that flat tappet often fails in jeeps. May have them pull the valve cover next week.

[SilverXJ]

Itc ould happen. How did you do the cam breakin and what oil are you using?

[bandofthHawk]

I bought the jeep when the motor had about 20k on it. I know the previous owner ran brad Penn oil. I talked to the guy who built the motor once he said I could run whatever in it. Pretty much used whatever. Synthetic blend midgrade basic stuff.

[SilverXJ]

I talked to the guy who built the motor once he said I could run whatever in it.

Thats not really good.

[bandofthHawk]

Ah bummer...well the problem was with the brad Penn oil it had the zinc and phosphorus but it killed my pre cats (2000 xj) I suppose the cam could definitely be worn. I guess it doesn't take much driving to wear out a cam with insufficient lubrication.
so how severe of a job is a cam replacement? No need for a complete overhaul I would think

[SilverXJ]

If the cam is in question I would recommend taking the engine apart, inspecting it and cleaning it well. Keep all parts in order so they go back where they cam from is they are good. Replace cam and lifters. The reason is that as the cam wears metal gets pushed around the oiling system.

The cam can be swapped out with the engine in the vehicles. But the head must come off and the front of the engine has to come apart. The front header panel can stay on, but the grill must be removed (easy, a few screws). The AC condenser cam stay in, just prop it up with a piece of 2x4. You could do this and so several oil changes to get the metal out. But I do recommend a complete tear down and cleaning.

[bandofthHawk]

Ok good to know the engine shouldn't have to come out entirely.should I use the same comp cam? Or try something different? Does the intake manifold have to come off? If so I would go ahead and do motor mounts and a new header and try to eliminate pre cats....hate those ca emissions bs.. Silverxj I see in your description you are using the same comp cam 68-232-4 ...have you ever had any issues with it? What kind of oil should I be using?

[SilverXJ]

You can lift the head and manifolds in and out as one if you have a hoist.

There are a lot of cams to choose from. However, you might want to find out what springs the head has. From what the builder said about the oil it sounds like he has no clue.

[bandofthHawk]

So silverxj thanks for the information I really appreciate it. I saw your build list you're running the same comp 68-231-4 cam? Would you recommend it to others or ever had any issues with it? What oil do you use? Would a roller cam be a safer option as opposed to flat tappet?