`97, F150, 4.2l v6

Getting P0303, cylinder #3 misfire. Have changed plugs, wires, and coil pack.

What is next, injector ?? or something else ???

Thanks

 

I had the same code earlier. It wound up that after a snow melt, moisture was in the hole where the plug goes, causing the coil pack to arc. I wound up taking the coil packs off, drying them, and using compresses air to dry out the spark plug cylinders. Runs like a champ now.

Be sure to check all of the electrical connections. If you replaced the plugs and the coil pack, it seems that the injector might not be working properly. You can by an injector tester (noid light) from an Auto Zone or similar store, pretty chep to test it.

Other than that, I'm not sure...Good luck, and be sure to let us know when you do find the culprit!

 

The 4.2s don't use coil packs like the Tritons... they use the "old" style. The spark plugs are near the manifolds and have spark plug wires running to them.

 

Any ideas with this 4.2l and p0303 code, other than plugs, wires, and coil pak ??

 

It could be either a compression issue or a fuel issue. Time to stop throwing parts at it and do some troubleshooting. First off you need to check the compression with a compression gauge and verify that everything is within specs. If that is low, then squirt about a tablespoon of oil into the cylinder and repeat the test. If that helps, then the problem is worn rings. If it doesn't help, then the problem is due to a valve, cracked head/block, or a blown head gasket. If compression is fine, then verify that the ignition system is in fact producing a strong spark on that cylinder. Don't assume that since you replaced parts that they are working.

If those things check out, then it probably is an injector problem. Those are harder to check, but if you have a mechanics stethoscope, you can use that to see if it sounds the same as the other injectors.

 

ok, here is an update. still getting code. i have ruled out, plugs, wires, and injector. compression check ok when compared with other cylinders.

most of the time, the engines runs smooth (no miss), sometimes you will feel a slight miss and others times the miss is really bad, then is when the cel will flash off/on for awhile.

question, my coil pak is a single "six pack module", do 2 oposeing cylinder coils fire at the same time (1 being compression stroke, 1 being exhaust stroke) ??? if this is the case, i could move plug wires between the 2 ??

edit: i am having to refill my coolant bottle every couple of months, but see no leaks !!

 

i thought i would give an update if anyone is listening.

problem fixed.

bad lower intake gasket. was breached between coolant and intake passages for cylinders 1 and 4. this does not explain code of cylinder 3 misfire but gasket was bad. surprised me that was running at all.

 

That intake gasket failure is what causes most problems with the 4.2L V-6 in these trucks. Many don't catch this before a cylinder fills with coolant and hydro-locks the engine which spells the end of the engine in a lot of cases. Glad you caught it before it took out yours!