1st post here and I need some help.
2003 F150 XLT Flareside 2WD 4.2 auto w/92K miles.

When in overdrive mode (~1300 rpm between 45-52mph), it seems like the overdrive is trying to upshift but it doesn't. It bucks noticably a couple of times until I either slow down or accelerate out of OD.

I bought the truck used at 72K and had the trans fluid changed right away. I asked the shop if they used Mercon V and they said they used an additive to make the fluid the same as Mercon V.

The only other thing I did recently was to change the plugs (not the wires).

I'm not sure if one has anything to do with the other but the problem started about a month ago.

For now, I'm driving in town with the OD off.

Any help is appreciated.
blip

 

That makes whatever fluid they used something like MERCON V. Not in my transmission, they don't! That's almost certainly not your problem, though.

It's probably the wires. It's possibly a coil going bad, but the wires are more likely.

 

I found out about after I found this site. You can quarantee it won't happen again.



I'll check that first and report back.

Thanks.
blip

 

The shop said they could only replicate the problem a couple of times but only enough to say it WAS a miss in the engine.

They got the diagnosis by power-braking it.

Their opinion was a bad plug from Motorcraft or it was damaged during the install. So today I decided to go ahead and try to replace the wires just to make sure. Now I can't get the wires loose from the firewall bracket

 

My intermittent miss turned out to be the coil pack.

 

How frequently did it occur (circumstances) ?

 

Hi there. Noobie here. I've got the exact same prob as blip.
Is it wire, plug or coil pack? What's the easiest way to distinguish? Any help is greatly appreciated.

 

I'll answer my own post.
It turned out to be the plugs AND wires.
It was the trucks 1st tuneup.
132,000 miles. Not too bad.

 

Cold? It's not reasonable to expect an immediate response when you tack a post on to a thread that hasn't had any activity for over 2 weeks..........you will get a MUCH better reception if you start your OWN thread and be as detailed as possible.

 

Roger that glc.