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Recurring problem #1 cyl misfire

OK. I’m getting a P301 code on the OBD in my 2000 Expedition (5.4 L). Already replaced plugs x 8, coils x 8, & fuel injectors. Still have rough idle when it starts up, usually for a few minutes & then it’s mostly OK. Maybe a small rumble now & then when @ a red light, etc. Replacing fuel filter & all 4 o2 sensors tomorrow. After that, I’m out of ideas. Help!

As you have discovered, spending money based on guesswork can get very expensive…

How many miles on this vehicle? Throwing expensive parts at it is NOT the answer…

As Caddyman notes - stop replacing stuff willy-nilly.

Your next step is to check the compression. This does not involve any guesses about parts.

Well, you guys were right. I have an honest mechanic & he said the same thing. #1 cyl checked at 30 lbs. He said he did a “wet test” and there was no change. I’m taking the sensors back & putting the $$ towards whatever comes next. Can y’all suggest what might be wrong and if any tests or inspections can be done to see what might be broken?

It's not compressing properly. He needs to now run a leakdown test to see if it's rings (rebuild), valves (head rebuild) or just head gasket.

Has this engine overheated by chance?

Thirty pounds of compression and no change after a wet test generally points to a cylinder head valve problem.

The engine did overheat. On the way home from replacing the #1 plug and COP to try to repair, you guessed it, #1 cyl misfire - P0301. Short answer is I think the cyl went down first.

You may get lucky, and just have a huge break in your head gasket. As per OK’s post, the rings are most likely OK. The leakdown will point at either the valves or the gasket. Either way, the head has to come off. Since it overheated, you most likely will need to have it surfaced, if the valves are OK. If not, then that cylinder (at least) will have to be done.

Then you get into the whole “I’ve gone this far, do I keep going” tail chase. Your mechanic will have to look and see what needs to be done inside.

Check the value of this vehicle before you go too far, but most likely it’s worth fixing. Watch for damage to the other bank, as the overheating may have caused some over there, too. values the XLT at $4785, and the Eddie Bauer edition at $5896. Of course, that’s in good running order.

Good Luck!

Thanks Chase and everyone else. Vehicle’s a great ride & I’m expecting a lot more miles out of her. I’m going to let him look into it a little more in depth & recommend a way to get it fixed.

It’s possible that if coolant entered the combustion chamber through a head gasket breach a valve face and seat may be disentegrating as hot coolant can act like a grinder on hot valves.