[itasor]

My 98 TJ is under warranty since we got it not that long ago, and the dealer is doing their best to fix this issue. I just figured I would post to get some other opinions. Wrangler has a 4.0 and it has 33,000 miles on it.

When we first picked it up, the CEL started flashing and then came on solid and when I scanned it, there was "P0463 - Fuel Level Sensor Circuit High Voltage" and "P0303 - Cylinder 3 Misfire Detected".

The dealer replaced the spark plugs (they said the wrong type were in there), but the light came back on so they ordered a new fuel pump.

Today I had the fuel pump installed. On the way home, the CEL started flashing so we brought it back. The light wasn't on solid, but their scanner showed that it was flashing because of misfires. They thought there was some carbon in the engine, so they did a Mopar Combustion Chamber Cleaner application and put some cleaner in the gas tank.

On the way home the second time, the CEL started flashing again and then went solid. I decided since it was solid I would scan it. This time it had: "P0300 - Random/Multiple Cylinder Misfire Detected," "P0301 - Cylinder 1 Misfire," "P0302 - Cylinder 2 Misfire," and "P0303 - Cylinder 3 Misfire".

I should mention that it seems to be running perfect and accelerate/goes up hills with no issues at all. The engine FEELS great.

Now, the dealer suggested they order some parts which I didn't really understand. Something about under the valve cover, there are things that ride on top of the valves that should float but sometimes get stuck from carbon. I don't know much about engines and didn't get a chance to ask more about what he was talking about. They did do a compression test and said everything checked out just fine.

The CEL usually starts flashing going up a long stretch of hilly road, goes off at the top, and starts flashing again going down the hill. This lead me to believe it was still fuel level sensor related (fuel moves in tank going up/down hill), but flashing is supposedly an indication of misfire, and the Fuel sensor code is gone now anyway.

I'm not excited about them opening up my 4.0L with 33k miles on it. Does this sound like it could correct the problem?

Any other suggestions or advise?

Thanks!!

[onlyn8v]

I feel your pain. I have 14k on mine and as of yesterday it developed this knocking, ticking. Everything I can think of so far is fine, and I even changed the coil rail. My truck runs like crap and sounds like its making popcorn. I dont get a CEL!!

Im now going to have to take this thing to the dealer (which I HATE to do) and watch them throw parts at.

Fing great.

[itasor]

Originally Posted by onlyn8v

I feel your pain. I have 14k on mine and as of yesterday it developed this knocking, ticking. Everything I can think of so far is fine, and I even changed the coil rail. My truck runs like crap and sounds like its making popcorn. I dont get a CEL!!

Im now going to have to take this thing to the dealer (which I HATE to do) and watch them throw parts at.

Fing great.

Well, that's the weird part. Mine runs perfect (like brand new), it's just the light that says something is wrong. I still think it's got something to do with the fuel level sending unit/pump assembly, but I don't know much about this stuff.

[ballallday89]

I just got mine on last night. I replaced my plugs and wires and dist cap. But i did misfire when i put the wires in the wrong order. It runs perfect now but the CEL just came on. i have 22,000 miles on a 98

[itasor]

Originally Posted by ballallday89

I just got mine on last night. I replaced my plugs and wires and dist cap. But i did misfire when i put the wires in the wrong order. It runs perfect now but the CEL just came on. i have 22,000 miles on a 98

Wow, low mileage! Let me know if you figure out why the light is on...I will do the same.

[ballallday89]

Will do bro. Im planning on taking mine in. Just because i hate driving with that light on even if it feels fine ha

[4x4grey88]

I have a 98 TJ (with 100K) and the CEL flashed while driving up hill and the engine seemed to have no power. The computer indicated 'misfire on #4).

I changed the wires, plugs, and ran seafoam in the gas tank with great results.

Yours might also be having fuel pressure issues and can be checked on a Dyno.

[itasor]

Yeah, I'm not sure why they just replaced the plugs and stopped there. It seems like if there are misfires, the first thing you would do is a full tune up.

[Harvo]

Try the Crankshaft Position Sensor. I fought a randon multiple cyl. misfire for a year. Tried new plugs, the cleaning treatment that you had done, and all other kinds of "snake oil" solutions. Finally turned out to be the CPS.

The day I bought the Jeep, that sensor went out and made the Jeep stall. I bought one at Autozone and the Jeep ran perfectly, but started giving me the 300-306 codes.

I fianlally read a post on here about the factory part having a cardboard shim that aftermarket CPS units don't have. That shim gives you the exact spacing when you install the sensor. If it isn't exact, you get codes, but the engine runs fine.

I bought the factory part for $80 and I haven't had a misfire since.

[itasor]

Originally Posted by Harvo

Try the Crankshaft Position Sensor. I fought a randon multiple cyl. misfire for a year. Tried new plugs, the cleaning treatment that you had done, and all other kinds of "snake oil" solutions. Finally turned out to be the CPS.

The day I bought the Jeep, that sensor went out and made the Jeep stall. I bought one at Autozone and the Jeep ran perfectly, but started giving me the 300-306 codes.

I fianlally read a post on here about the factory part having a cardboard shim that aftermarket CPS units don't have. That shim gives you the exact spacing when you install the sensor. If it isn't exact, you get codes, but the engine runs fine.

I bought the factory part for $80 and I haven't had a misfire since.

Thanks, I will add that to the list of things to do before they jump into the valve springs or something major. Who knows, maybe there is an aftermarket one in there now. Is there a way to check the CPS to see if it's bad?

[itasor]

So they ended up doing the valve springs and scrubbing carbon while it was open. Still no change. CEL still flashes while going down hills. Now they want to pull the head and clean more carbon. I still think it's a sensor of some sort and pulling all these engine parts is a waste of time.