Here's the story.
We were on vacation last week with our 2001 Ford Expedition. Pulling our camper through some hills, 110 degrees out. The expedition started to miss. At low speeds it is a hard miss, higher speeds it smooths out but still lacks power, still missing. The check engine light is on solid part of the time, flashes part of the time.
I made it 60 miles and stopped at a shop. The mechanic did not have time to look at it, but let me use tools I needed. Scanned the vehicle, it showed a miss on cylinder 1. No other trouble codes stored, nothing else showing.
I changed the coil pack on 1, it didn't help. I changed the spark plug, it didn't help. The plug was only a year old, but was burned. Not fouled but slightly burned. I switched injectors but the miss did not follow the injector, so that ruled out an injector. I am getting good hot fire from the boot out of the coil pack, so definately getting spark.
So, we continued another 120 miles. No change, still missing the same.
I suspect a problem with the intake manifold, either a gasket or a cracked intake. While I was messing with trying to find the problem, I took off the oil fill cap to look in and see what I could of the valve train. When I pulled the cap off the engine idle changed. Also the air conditioner fades in and out. I recharged it so it is good, but it goes from cold to warm. The air conditioner fades as the check engine light changes. When it blinks it blows warm, when it is on solid it blows cold.
This tells me I have a vacuum problem, but the miss is still isolated to number 1.
When I stopped for the night I sprayed WD40 around on the intake but did not locate a leak.
I tried to do a compression check tonight but my compression tester does not have long enough threads to screw into the plug hole. I did try to stick my finger in the plug hole when it was running. Don't do that! It does have compression, but I don't know how much.
So, any thoughts? Intake? Broken valve spring? Burned valve? All 3?
It is a 2001 Ford Expedition, 170,000 miles on a 5.4 Triton. In the past 170,000 miles I have changed the alternator, changed rear brake pads and replaced the EGR pressure sensor. Other than that it has been trouble free.
Oh, and I am not getting water in the oil, not getting oil in the water, and not getting pressure in the cooling system so a cracked head or blown head gasket is not likely. Also it had been running cool, never gets hot.
It misses until the rpm's get up over 2500, then it smooths out a little.
It was still getting 16 mpg.
Any ideas?

Oxygen sensor?

It was used too much when it was new.

Are you sure your math is not a little off on the mpg ? If I could get 16 mpg I would buy an Expedition.My 02 F250 with 5.4 barely breaks 9 mpg with 3.73 axles.

And here I thought my truck had all the weird, "undiagnosable" problems! You are outside of my area of expertise (meaning, THAT hasn't happend to me yet)

Fwiw, my check engine light is currently OFF after being on for almost 2 years! Success! Ha!
What I love about it though, it just keeps on chugging. It might have ran a little rough here or there, but it still brought me home reliably. Sounds like yours is still chugging too. Give it a lil TLC for its efforts. Good luck!

your engine idle changing is normal with the oil cap removed as you are giving the pvc system more air, which gives it a vacume leak in a round about way.

you need to take a compression test before replacing any more parts, you may have a burnt valve or piston, but more likely valve. unhook the crank semsor or something so it doesn't start when doing this.

I'd start by doing a leak down test on #1 cylinder

The rocker fell out in my wifes darango. Gave me heck trying to figure that one out. Could be the problem if it has an over head cam.

Best way to fix it is to screw the radiator cap off...and drive a chevy up under it lol
Sorry just had too

Valve. You have to kill the fuel and hold the throttle wide open to do a compression test. That's all that's left

Tim.

In my opinion (this is not advice) from the description you gave is that you have an oxygen/air leak, leaking head gasket, valve, cracked head, block, leaking cylinder, spark plug, injector or the theads, and depending on style intake manifold, and so forth. If I couldn't isolated the leak by sparying I would use a OEM recommended block sealer to see if that worked.

Found On Road Dead! 400,000 miles on my last Tacoma 4X4 No major problems routine maint brakes and clutch biggest outlays of cash. And it ran like a champ got 20MPG but then late one night I met a drunk on the highway. New Tacoma 4X4 24MPG looking forward to another 350,000 miles or more.

try swaping coil pacs. i have had them "open" after they get warm and or damp. easy enough to do. the 5.4's are noted for the coil on number 4 to go bad. water drips from the hood. yes i did see you had changed it. sometimes new ones are bad also.

Just because the scanner shows you a code that says its missing on cylinder one does not mean its a problem that is strictly involved only with cylinder one. I went thru this a few years ago with a truck, it was giving me a misfire on a certain cylinder number. Long story short it ended up being a dirty egr valve on top of the intake, had nothing to do with the cylinder it stated but that cylinder was the first to misfire and so it read that way. A mechanic told me once that it could be something so simple as a fuel filter or even water in the gas and it would throw the same code. Its not necessarily always a problem with that particular cylinder, it could be just that cylinder recognizing a problem first

I may have given too much weight to the plug being burned.
This is what I originally thought:
It seems to me he has isolated the problem to the #1 cylinder. He wrote that he has a burned plug in the number 1 cylinder, not fouled but burned. My understanding of that is that the plug in the #1 cylinder has a melted electrode. That’s a sign of too much air or too little fuel which both relate to too much oxygen/air and that can cause a hot burn. I only referring to an engine that is of it’s the original configuration and using the stock plugs with no modifications.


The slightly burned part has me sort of confused, is it melted what color is the electrode, tan, ash white, brown, rainbow, black?

He said the he changed the coil pack and it did not correct the issue.

I believe I have identified the source of your problem...

Thanks for the advice and ideas!
The plug was black and burned. The center electrode was not burned off. By burned I mean it was black and crusty but it did not have a bunch of residue burned onto it. Too much oxygen type of burn.
It is a steady hard miss on #1 for sure. I have unplugged the injector and the coil pack both while it is running, several times, and it still has the same hard miss.
On the mileage, according to the trip computer it was getting 16. We usually get 18 to 19 when running without the camper, so it dropped a few. The trip computer has always been right on with actual figures. I usually get between 10 and 12 when pulling our camper, but when the miss started it dropped down to 8 mpg.
I am going to find a compression tester that will work on this engine and do the compression and leak down test.
Oh, and no I will NOT be trading down to a Toyota! LOL! I hear they are great vehicles, but still a Japanese owned company. All of everyones talk here of foreign business going overseas and then to buy un-American vehicles? And I drove one once for work. It was JUNK. The most uncomfortable thing I have ever sat in. But that was 15 years ago, so they may have improved by now.
I will keep checking things and see if I can track it down. I may have to take it to a mechanic. I hate paying someone else to work on my stuff but it might be time.
Don't forget, this engine is like others, it has a plastic intake manifold.

A plug that is black with a crust over the electrode is most likely caused by oil, a hot plug will look ash white or melted not black with a crust. It still could be a leaking head gasket, block, valve seal, or anywhere that oil can get into the cylinder. Good Luck.

or not enough compression to burn correctly

Possibility 1 rings are broken or stuck
2. Valve burnt
3. Valve seats bad
4 busted valve spring

IMO a combustion issue would related more to preignition or delayed ignition, not combustion or incomplete burn. And if was an incomplete burn the spark plug would look wet and could have black soot too but not much of a crust.