I have a 2001 F-150 5.4 liter V8 with 151,000 miles. About every 5th or so startup (pretty much random) the engine runs very rough. It shakes much the same way as when one of my coils went bad or like the time when I disconnected a plug wire accidentally, so Im assuming its some type of misfire. Unfortunately it doesnt generate a check engine light. After a couple of miles it stops shaking and runs fine. It's been doing this for about 2 months now.

It never does this while driving, always when I first startup. The weather doesn't seem to effect it, it happens on cold and warm days. I've also noticed that in general its slow to accelerate, especially at lower RPM's. I put high octane gas in it and it accelerated wonderfully, it also didn't have the shaking problem, but it happens at random so it could have just been a coincidence.

I've ran 3 different fuel cleaners through it, and it hasn't made a difference. I just changed the plugs, PCV valve, and fuel filter 6 months ago. A buddy of mine thinks it is caused by carbon buildup which is causing detonation. He suggested I run a can of top end cleaner through the intake manifold. I've seen several posts on the net about Seafoam, but also have read that it can be harmful to the engine. I'd like a way of knowing if it is in fact carbon buildup before I do something like Seafoam.

Is there a way to determine in fact if its carbon buildup? If its not carbon buildup any other possible causes? If it is carbon buildup is Seafoam the best choice or is there a better alternative?

P.S. I'm getting a ScanGauge II soon, I'm not sure if that will help with diagnosis of the issue or not.

P.P.S. I put Bosch Platinum 4 prong plugs in it. My buddy swears thats the problem because they are crap....I have my doubts though.

 

I went through a similar problem about six months ago. Engine would not throw a code, but then it started running rough more and more often. Like you, I started doing all the obvious things, but it just kept getting worse and worse! It would not throw a code (I borrowed a code reader from Auto Zone a couple of times) and no check engine light.

I had ruled out the spark plugs, because I had put in new Bosch plugs less than 20,000 miles before.

Finally, the truck started running one cylinder down ALL the time and the SES light came on. I Immediately limped to Auto Zone to borrow the scanner. Misfire on #6! I bought 1 new Motorcraft plug, limped home, and pulled the Bosch plug out. The little tip in the middle that the spark jumps out from was GONE. Totally erroded. Put in the new Motorcraft plug, and the motor purred like a kitten.

Since then, I've replaced all the Bosch plugs with Motorcraft. I had read horror stories about the Bosch plugs before, but I was skeptical. Now I know I will never put another Bosch plug in any vehicle I will ever own. They may make other products that work, but their plugs suck in our trucks.

 

Thats your problem, the Bosch plugs. Switch them!

 

Put a set of Motorcraft plugs in there.
I bet your problem gos away!

Phil

 

If it's not the Bosch plugs, it's weak cops.

 

How do you know? Last time I had a bad coil it was a constant problem, not only when it first started up.

 

Yeah, they're probably NFG plugs, Motorcraft seem to be the best, but beyonf that, maybe the IAC is gummed up, along with the t-body. Try just cleaning these and maybe the MAF sensor too, it's easy and should be done anyways.

 

Right!! When those Botch plugs eventually fall apart , where do you think the missing parts go ?