2003 XLT 5.4 misfire after weeklong rest

[Jarheadmatt]

Sometimes it takes a while for a code to appear. about 50 miles. In the mean time the ECM will adjust air and fuel to try and compensate for the lean/rich condition until it gives up and throws a code.

 

[1955moose]

Run a fuel pressure test as well. We need a baseline to determine if you may have a intermittent fuel issue. Should be above 35psi if lines are clear, and pump is ok.

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[Plati]

update .. 03 Expy sat for 6 days, started it this morning with BAFX in OBD port. Was running rough, let it run for a couple few minutes , no codes reported in Torque Lite, still rough. Drove it 2 miles and stopped/checked, now reported P03304 pending (not logged). Cleared it and drove another couple miles ... no codes and running smooth. P03304 is misfire on #4.

Most likely seems COP and/or plug. Heard a heater hose through there degrades ... making me especially suspect COP. 80K on plugs, good time to change them anyway.

Next steps unknown but I think it would be good to get in there , maybe replace hose, plugs, and COPS, and have a nice look see around area --- since I really like this puppy and would like to continue to drive her. Things like this usually get worse not better if not addressed.

On the other hand, I could just wait for it to get worse and do the work then.

 

[1955moose]

I'd change out plugs, coil boots, that one coil, and definitely that weeping hose. The bargain coil sets usually fail premature, is why I'd leave the other 7 coils alone. Let us know if this helps your stumble, rough idle situation.

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[Jarheadmatt]

I didnt attend to a misfire properly. Cost me almost $3K in catalytic converters. If emissions is important, take that into consideration.

 

[Plati]

Update. It rained a LOT and started misfiring in the morning even though I was driving daily. I dropped it off at my local trusted shop. They diagnosed the P0304 and replaced #4 COP & Plug. COP looked bad like at some point fluid got on it. Seems fine now, but time will tell. I had told them to do all 8 if they wanted but these guys didn't think it was required. We're trying to keep it running right but not put extra money in it because it could go to junkyard at any point.

Motorcraft parts --> FD503 Coil & AP103 Platinum Plug
Also got fuel filter $220.

Guy did say its best to fix a misfire ASAP dumps unburned gas into CAT and can ruin it. Definitely good to address it!

 

[1955moose]

That's what we've been preaching here for years. Fix any coolant leaks asap or they will sure as sugar fry that coil. I agree with your shop leave the other Ford coils alone, the aftermarket ones are trouble! And he's also right about destroying the cats. A rich mixture is suicide for them. Their very delicate inside. Your on right track for now.

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[Plati]

..... And he's also right about destroying the cats. A rich mixture is suicide for them. Their very delicate inside. Your on right track for now.

I have a connection to catalytic converters so I want to be nice to them. I worked at Corning Glass Erwin Ceramics plant around 1980. The plant was the first US manufacturer of catalytic converter substrates. They mixed up ceramic batch and extruded it through a die like play-doh then baked it in huge ovens. Revolutionized the auto emissions control and played a big part in clean air to breathe. Plant ran flat out and I was able to work double shifts any day I wanted for 2 years. Kept one for myself. Those tiny honeycomb channels get infused with a catalyst and have a lot of surface area.



Invention of the modern automotive catalytic converter