Sorry to repost this, but I just put it under the Rough running 5.4 and I didn't know if I'd get anything back. Thanks everyone!

I have almost 100k on my 99 5.4. It seems to idle ok, but when I get in the 2000 rpm range it will miss sometimes. Sometimes really bad others, not so bad. Then there are times with no miss at all. I did blow out a plug a couple of weeks ago and repaired it with a helicoil. Does anyone have a suggestion on what to try?

I put a can of sea foam in to try to clean the injectors and EGR. I will change out the fuel filter this week. What code should I be sending (on the little odometer trick)? No "check engine" light is on.

I'm just getting a little gunshy. The week after doing the helicoil I put 1500 miles on in 4 days with about 16-17 mpg at 75 mph in the mountains.

I put the sea foam in to try to clear up some pinging I got when I was accellerating up a couple mountains at about 70.

Any help is appreciated.

 

Are you still on your original plugs/wires? If not how long has it been since you replaced them?

 

I replaced the original plugs with bosch +4's around 65 or 70k maybe even more recent than that. I replaced #2 and the coil about 2k miles ago.

 

I finally got a chance to look at the truck last night. The same coil pack that I replaced had the boot all melted off. So I pulled that plug out and looked at it. It didn't look good. The ceramic under the 4 prongs was all shattered. The prongs looked correct next to a new plug, so I don't think there was contact with the piston. At the top of the plug where the coil pack makes contact with the plug, you could see where the spring in the coil pack melted into the plug. When I got the coil pack, I asked why it looked different from the old ones. There was just a spring at the end and not the spring with the metal insert that kept the spring from going over the plug. The plug even looks like it was kinda bent. But not the part in the head, the part where the coil connects.

I think I found the cause of the miss at least. I scanned it with an ODB-2 scanner and there were no codes at all. That's a little odd I think.

I ordered a new motorcraft coil pack. The failed one was a visteon. (Ok it's like Delphi and a GM.) It dang well better have the correct end on it. Hopefully it will all work out.

I'm definitely open to more suggestions.

Doug