Hey gang.... I'm pulling out my hair over this one.

Have a Roushcharger on my 2006 F-150 with 5.4 V8.

Four weeks ago I started getting misfires under load. Not enough to set off any codes but it was kill performance. Suspecting a bad coil, I swapped out all the coils (I have a set of stock coils and a set of performance coils) and put in new plugs (get them at cost). No dice. I haven't really driven the truck except to diagnose the problem.

Two weeks ago it got really bad. Anything other than very light throttle would cause the engine to misfire. Give it 20% or more throttle and a P0300 (random misfire) code would get set.

So now I'm wondering what is the most likely cause. I know its not the coils or the spark plugs (correct heat range, 1 lower than stock for the blower). If I can take care of this myself I'd rather do it than tow it to the dealer (the only Roush authorized Ford dealer is too far away to drive it in this condition). I know its not the aftermarket coils because the stock coils had the same problem but I know they'll try to give me grief over them (though I know my rights and how to push back).

Any suggestions? I've looked and cannot find anything obvious like loose connections. Have cleaned the MAF and that didn't help. Checked, removed and reinstalled the intake tube as well to rule out a leak after the MAF. Checked connections to fuel injectors.

It could be one of many things:

1. Fuel filter
2. Fuel pump
3. Vacuum leak
4. Loose ground wire

Where should I start? Might be time to start data-logging it....

 

The p0300 is going to be your pointer, it's usually indictive to an electrical fault. So I would start with grounds.

Fuel problems should show lean codes unless it's drastic, but sence you have a blower it wouldn't hurt to know what your fuel pressure is and if it's dropping with throttle. A vacume leak should also have a lean code accompany it.

You might try ragging on it and seeing if you can get it to narrow down to a specific cylinder. Random with cops will be a nitemare to diagnois.

 

I've tried flooring it. It will only throw P0300.

 

What are the plugs gapped at? I've had problems with both too large and too small of plug gaps...

 

Plugs on 2004+ F150s use a hoop that is pregapped. You don't normally gap them except in very special circumstances and that requieres a special tool because of the way the plug is designed. Plugs and coils have been ruled out.

 

I hate to say it, but it could be a coil driver in the ecm. I don't know the precedure to test it, but if you have a wideband you should notice higher than normal a/f ratio that can't be tuned down.

 

I got fed up with it and took it to the Roush dealer yesterday evening. Its their problem now.

 

That's probably the easiest thing until you have to pay them.

 

Its under warranty. Roush is the only company that keeps the Ford 3/36 warranty intact.

 

what was the problem?

 

Plug fouling. Running plugs now which are manually gapped to 35 to prevent blow out.

 

That's not all that uncommon for boosted applications. They can, over time, open back up too.

Did they install plugs with a slightly cooler heat range?

 

With the 3 valve there are 3 plug available:

HT2 - hottest. Sold on the 2004-2005 F150.
HT1 - mid-range. Sold on the Mustang, and replaced the H2 in most applications. The H2 causes more carbon build-up and causes problems with broken plugs due to the bottom getting stuck.
HT0 - for boosted applications.

Unless I go with Brisk brand plugs I cannot get a colder heat range for this engine. They are too new to be proven on these engines. Maybe in 6 months