P0303 cylinder #3 misfire

For rough idle the first thing to do is clean the throttle body and idle air passage. All it takes is some TB cleaner and an old toothbrush.

I had the same problem. Turns out on the 00's and 01's, there is a problem with heat soaking into injector #3 and cuasing a misfire. The fix is a heat wrap availible at the dealer for injector #3. I reset the code, replaced the plug and and haven't had a problem since.

HTH

Carl

With a misfire, I'd be looking at the plug wires or coil. I'd check plug wires if there was a distributor, or I'd look at the coil if there was a separate coil for each cylinder, or a coil for every two cylinders.

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Jeff, no plug wires or dist cap on an 00 and 01. Coil rail with three coil packs.

Carl

Interesting that you posted this at this time. I have a 2001 TJ with the 2.5 L with the same problem except I have a P0302 code. It is skipping bad. I am lucky enough to have an independent shop locally with a good, smart, reliable crew who has never tried to stiff me on any repair work. Dropped it off there yesterday and called them today to get some news. They found that one of the bridges across the valve rocker arms on cylinder two had broken. Part will be in tomorrow. Just more information for you in case you run into a dead end eventually. Hope this helps. Les

Some rails can develop internal leaks that cause misfire. If you can, try swapping packs and see if the problem moves. If it moves, it's the pack. If it doesn't move, it could be the coil rail.

If you have a good rpm gauge or ears you can try this. With the engine running, disconnect the injectors one at a time (just one at any one time though) and listen. There should be exactly the same drop in rpm. If you lift #3 and there is little drop then the injector or the feed to that injector might be bad. A mechanic stethescope placed on each injector will also give you a clue as to how they are working. They should have a clanging sound and not a dull thunk.

Also remember, with coil rails and packs, plugs fire in pairs. I think this is the correct pairing. don't have the schematic to look at.

1 5 3 6 2 4 1 6 5 2 3 4

So, one of the coils is bad.

Or it's electronic plug and socket are dirty.....

Mike

Jeff Strickland wrote:

There is only one plug, at the rear of coil rail. Three coil packs are on the rail.

Carl

If a coil was bad then two cylinders (3 and 4) would be misfiring.

agreed.

It can also be the rail. I've seen where the rail has failed internally and that was causing the misfire.

Ok, but for one coil power two cylinders I would think there is one input connection on the coil to rail and one connection going to each plug with a connection at each plug, no?

Haven't seen the setup yet.

Mike

bllsht wrote:

IIRC, five wires. three ecu grounds, two ecu battery. Plus and one connection for each plug

What connects the spark plugs to this pack?

Thanks,

Mike

bllsht wrote:

The coil rail.

It looks like the packs are molded into the rail. That sucks especially if one pack goes bad.