I have a 2001 F150 sCrew with a 5.4 with 104k on it. The past couple days it has "stumbled" a couple of times. I'll be running down the road at about 50mph - more or less - and let off the gas to just kind of coast. When I gently ease back on the gas, I get a little miss, or a stumble. Happened two or three times in the last 100 miles.

The fuel filter doesn't appear to have been changed recently. I thought I would brake clean the mass air thing in the air filter (read that on here somewhere). I have no idea of the condition of the plugs - might be time to change them.

Any advice/thoughts?

 

There is a coil gone faulty. It won't set a code so that leaves you with a decision, replace all of them or get a dealer stress test to pick out which one it is.
There is an involved reason why this acts this way and no, a fuel filter won't cause this kind of driveability problem without showing up under heavey power throttle..

 

So Bluegrass 7, how sure are you on this one?
I changed the fuel filter, and it didn't solve the problem. So, you're 1 for 1.
Anyone else want to second the opinion before I go out and buy a set of those COPS things? I suppose I might as well change the plugs if I am in there anyway.

Hate to be sceptical, but I think I'd be in for a couple hundred in parts for COPS and plugs - not mention out a day or so to change them.

 

How does it run at idle? And if a coil goes bad it should throw a code. But if it is a plug it won't. You are at 104K. I had a plug foul at 100K. I would start by changing the plugs (cheepest and it needs it anyway) then if the problem presits go after your coils but like I said it should throw a code if the coil goes out and it will tell you which cylindar. Make sure you clean your throttle body as well.

 

A coil causing that kind of stumble won't set a code because it's not a total failure.
To pick it out you need a dealer stress test to find which one it is, or change all of them and hope you don't get another faulty one in the bunch to cause you to think it's not a coil..
What the problem is:
One or more coils has shorted turns and causes low output voltage and loss of reserve voltage to fire the plug under the 'SPECIFIC' conditions of cruise, light throttle and very lean A/F mixtires nearing 20 to 1 that require the coils near max voltage.
When increased load is called for the A/F goes richer and is not as hard to fire requireing less coil voltage.
Old plugs will add to the issue and may appear to clear the problem for a short time then it will come back after the plugs get some run time, because the original fault is still present..
Do it or enjoy the hassle.

 

jjlogue3 - thanks for the input!

Bluegrass7 - thanks for the additional information! I'm thoroughly convinced and will purchase a new set of the coils and plugs this week and attempt the job myself. It certainly is just as you said - when I am above 1500rpm it doesn't seem to have any problem, it seems just when it is in that real lean (feathering the pedal) and low rpm (less electrical current?) that I have the stumble.

Thanks for the help. Anyone want to come to North Carolina and change plugs for fun?

 

I neglected to include in the cause that the EGR also opens, fuel is cut back and the ignition timing advances to make things more complicated, so there are a lot of things going on that most don't know about.
If this problem gets bad enough, it at times, can feel like the motor shuts off for an instant then comes back on. This is because the PCM gets an undesired signal and upset signal processing until the duration clears. This is the instant shutdown until the PCM recovers normal processing again. The PCM dosn't know what to do with the problem at the time.
The reason their is no code set is the faulty response dosn't happen a sufficient number of times in sequence to trigger a logic code and ID the cylinder before the the fault table is reset by a change in throttle and power request during driving. That being the case, the PCM can't ID the offending cylinder.
The fault detection is by several means but the one that sets a cylinder code measures the rotation time of each cylinder as a means of detecting a cylinder not contributing the same to engine power as all the rest within narrow limits. That's done by looking at the crank sensor signal for rotation time.
Now you have all the info to go with and you thought it was all easy.
It is now!
Good luck.

 

mine did just as described at 99,975 took it in and they changed plugs then tested and found a bad coil. in and out in 3hrs.

 

I wouldn't be so fast to throw cash at the problem & would employ an old reliable check 1st. Have you priced the COPs yet? Note FORD recommended 100K for spark plug change.

I'd be prepared to change the plugs & carefully examine each plug tip as you remove them. If you have had misfiring in a single cylinder it should show up on the plug as an odd color. Expect clean running cylinders to be tan & a misfiring cylinder to be darker. If you find an obviously discolored plug you've identified which cylinder is missing. A single COP may be all you need.

 

you may not need cops at all but just the boots and connectors attached to the bottom of them...

 

yeah i wouldn't recommend pulling the ol' shotgun out of the toolbox and firing a set of coils at your truck just yet. Do as Bluegrass7 advises and have your dealer run a stress test. It'll tell them which coil is dropping off under load. A single COP unit is like $98 and some change OEM, and at least $50 for a trustworthy Borg-Werner from a parts store. I was lucky enough to come across a full set of new Motorcraft coils on Ebay for $175.00 last week, and i just got them in the mail and will be installing them tomorrow night to fix a similar problem on my '98.