Hello All,
My daughter drives a 1999 4.2 F150 AT. 49000 miles with a recent tune up consisting of new plugs, oil/trans change/ radiator flush.. I've been running a JET chip in it since it had 5000 miles on it.. It has run flawlessly.

Today I needed to borrow her truck so it is the first time I have driven it in months. I noticed that it was running really rough during acceleration and right around 2000 rpm. On the Freeway at freeway speeds it seems ok.

Took it to a mechanic friend who put it on the scope. At first it appeared to be a clogged fuel injector. We cleaned the injectors but later found that there was a misfire on cylinder #4. He pulled the plug and it appeared ok.. it only has about 10k miles on it. By the time we finished checking it.. the shop was closed.. I am suppose to take it back in the AM. Meanwhile, I was wondering if anyone had any other thoughts? Plug wire? or ??

Thanks for any tips.

Bill

 

Hello!
I have a 1997 4.2 V6, and it has been known that the engines made for these early models have a lot of trouble, so this may not be your situation, but here it goes.
Mine started same as you, with the misfire, and it resulted of a coolant leak through the intake manifold gasket. Got my truck from the shop today. The compression tests resulted OK, so I believe the head gaskets and the front cover gaskets are still holding... Scottie, are you listening?
So anyway, I do not want to scare you, just wanted you to know.
Still it might be some other less complicated situation. Maybe you should ask for them to be checked.

Hope this helps.

Robert

 

I had a plug wire go bad on #2 at about 20000 miles so that could be it

 

I'd look at the plugwires first, then consider a bad plug next. Yes I know you pulled the plug, but as you pointed out it runs good at highway speeds so the plug can look pretty normal.

I'd go wires first.

 

I agree with TallTomG. Some members of this community have reported bad coil packs, so you might consider that.

 

Thanks for all the input... I'm on my way to the mechanic.. Ill let you know what I find out!!

Bill

 

Thanks to everybody!


We narrowed it down to the plug wires or the coil block... I went to the Ford Dealership and they wanted $110.00 for a wire set... So I went to Kragen and bought a $36.00 set. I figuered I could buy two more sets for the price Ford wanted.. anyway.. worked like a charm.. I put the Jet Chip back in and there is not one ounce of missing or sputtering.

Thanks to everyone that chimed in..

Bill