P030 - Misfire 3rd cyl - rough idle at start up

[Jim Jermain]

Recently my '00 4.0 OHV Explorer (74K miles) recorded a P0303 misfire on the # 3 cylinder. It set the code right at start up when I tend to get a rough idle for only about a minute. I have changed the upper intake plenum gasket and after it set the code I pulled the fuel rail, replaced the fuel rail gasket and all the injector o-rings. I tightened up the fuel rail studs and also torqued the intake manifold bolts to the proper spec. After I put it back together it ran perfect for one week. However after a week my rough idle is back at start up. It has not set the DTC. However I suspect that is coming. I'm thinking it is either a bad fuel injector or a bad lower intake manifold gasket. Any suggestions on trouble shooting?

I've tried pulling the #3 plug after the car sits overnight (when the rough idle is the worst). I did not notice any gas or antifreeze on the plug. I also tried pulling the plug wire and cranking over the engine to see if maybe there was gas or antifreeze down in the cylinder and would fowl the plug at start up. I couldn't see anything.

I really appreciate any tips.

Thanks,

Jim

 

[2000StreetRod]

Possible misfire sources

You may want to take a look at my in progress thread Engine misfire procedure for some ideas.

 

[Jim Jermain]

Thanks for the post. All good thoughts. I think I will change the fuel filter just to be safe and then go after the intake gasket or fuel injector.

Jim

 

[Opera House]

My 97 (even though I don't own it any more) still has a problem with #4 plug and suspect antifreeze. It randomly looses small amounts. Replacing it 2-4K was an expedient solution to the problem. I have a nice B&L microscope and never could see anything obvious with the plug, but replacing it always solved the problem.

 

[2000StreetRod]

swap plug & wire

Replacing the fuel filter is a good idea. Especially if its been more than 30,000 miles since the last replacement. I suggest adding a bottle of fuel injector cleaner after the filter change.

Faulty ignition is the most likely and easiest to correct source of misfire. If the wires will reach, you may want to swap the plugs and wires for cylinder #3 with another cylinder to see if the misfire moves. While you have two of the spark plugs out, you may want to test the compression of each and compare them.

 

[Jim Jermain]

Thanks for the additional tips. Before I purchased the truck from my parents the local Ford dealer tried to chase the misfire as well. They replaced all the plugs, and plug wires. They also cleaned the fuel injectors. $400 later the problem was still there.

 

[2000StreetRod]

compression test

Sounds like more reason to do a compression test.

 

[kegabeer59]

plug removal

how do I get to rear spark plug on passenger side..driving me crazy

 

[2000StreetRod]

rear spark plug

jack up the right front, install jack stand, remove wheel, remove inner mud flap, remove spark plug working thru wheel well.

 

[BlownSkillet]

Hey Jim, did you find anything wrong that corrected this problem? I'm rebuilding the front end of a 00 OHV Ex for a young lady and hers does the EXACT thing at start-up that you describe. I have found nothing so far.