Had a cel for a while now, just got around to borrowing my friends scanner to check it out. To my suprise it was throwing 5 codes! P1494 something about emissions, P0300 random/multiple misfire, P0301 cylinder 1 misfire, P0303 cylinder 3 misfire, and P0305 cylinder 5 misfire. Needless to say there is a knocking at idle I could tell something was up that's why I checked it out. Anyone know the source of these or a way to fix it? It's my fathers truck as much as it is mine and he was ignoring the cel so i'm taking it into my own hands now after seeing all of this lol. Guessing it's a timing thing if half the motor is misfiring but I have no clue

 

I would start with tps

 

Repeated misfire codes. Mine are some combination of the first four injectors mostly. So far, I have replaces the plugs twice, coil pack, three injectors, (the other three will be done new years weekend), and also I will do the fuel module on new years weekend. I cannot get mine to pass emissions due to this. Its very random, often running fine for nearly two weeks before the event comes back. I have taken pressure readings on the rail, and they are rapidly fluxuating but are in the 40-44psi range.

What year is yours, and have you tested pump output pressure? Does your misfire get worse when sitting at an intersection or restart with heat soak?

During this episode it threw a code for evap system small leak- the gas cap replacement took care of that. However, my multiple misfire still comes in. If the work I do this upcomming weekend cures it for good I will let you know.

 

it's a 2001 and this is why i havent messed with it yet i dont wanna buy a bunch of parts that wont fix the problem let me know if you find anything out id really apreciate it

 

To tell you the truth i have no clue what heat soak is lol and i havent tested the fuel pressure but the only problems im getting is a bad knock and a large loss of power

 

Heat Soak is when the vehicle is shut down and temperatures under hood increase, aging or faulty electrical components are suseptible to failure or begin to fail with this condition.
My problem is definitly related to heat soak, because it only rears its ugly head when idling for extended periods or hotter days.
Have you determined the nature of your knock yet? Is it only at idle or when driving? Different levels at different RPMs?

 

check the tank for contaminated fuel.. Drop the tank

 

Stop!

Since your rig is a 2001 it has a 0331 cylinder head. Get a compression tester and check all 6 cylinders before doing anything else.

Remember, 3 full compression strokes per cylinder with gauge installed.

 

Thanks for all the tips, mine doesn't suffer from heat soak or much else for that matter. The only idication of something being wrong is the loud knocking coming from the firewall while in the truck while it's idleing and the cel. The knock sounds like it's happening everytime the crank turns over, definatly sounds like it's just the cylinders not firing right and making a symphony of pain. I will have to grab a tester and check the compression, I'm thinking it has to do with the valves or something since I read up on this tsb saying the exhaust valves get covered in carbon buildup and stop rotating properly. I'll test the compression and match it to 3 strokes and see what happens, if I find nothing from that I'll have to rip the head off and check the valves. It's just so frustrating that this truck has less then 70k miles, we take good care of it, and it's only been to north carolina and back twice and seen about a full 24 hours of offroad time and nothing serious at all.

 

Does this engine knock at idle and only on acceleration " all the time ?" only cold and or only hot ??? does it come and go, or is it constant whenever you let it idle or accelerate? only reason I ask is cause one time in my life "and I have been around alot of 4.0 litres" but I found a broken nose cone on the starter.. I was planning on removing the engine when I found this.. A 4.0 engine is a really tough engine, have seen worn lobes on cam shafts , bad lifters , broken valve springs and the valves covered in carbon from not rotating"tsb" . but rarely a wiped out rod brg or crank. keep that in mind...

 

Only at idle cold or hot, seems to be a bit worse when cold however. I'm not doubting this thing won't keep on kickin for years to come it's just not running properly and shouldnt be ignored because it's known for longevity atleast i think lol. By the way you don't really notice it when you accelerate mostly just at idle and I know this seems to be common on most jeeps but the tach never sits flut it fluxuates very slightly up and down rather then sitting still and the exhaust sounds a bit lopey almost like a cam can you post video on this site? if so I'll try and get one.