Hey guys,
Problem surfaced about 3 months ago....While in 4th gear, with the torque converter locked and steady speed maintained, the trans feels like its slipping. If I give it a little gas and unlock the converter, it goes away. If I let out of the gas, it goes away. If I hold the gas, the slipping is accompanied by a vibration/ bounce. No codes and it doesn't do it with OD locked out. No miss at idle or on acceleration. Trans has been serviced every 35,000 by Ford. Fluid is clean, and not burnt. Any ideas?

 

For what its worth...

My 05 had similar symptoms...turned out to be a bad coil on #3 cylinder...dealer chased it for several weeks, changed trans fluid, fixed broken snap ring, TSB on valve body... after all of that bad coil...

 

How many miles are on the spark plugs? Definitely sounds like a low grade misfire.

 

plugs or fuel filter same thing mine was doing last year, and once i got those done back to perfect

 

I had the same problem on my 2002 F150 4x4 (5.4 ),Changed the trans fluid ,still had the problem..Turns out after a diagnostic ..It was # 5 cylinder was misfiring ..Torque converter lockup will drop your rpm while under load in 4th gear...You won't feel any miss at idle or acceleration...

 

Whoa! So glad I read this. Same problem with my '05 Lariat SCREW with 160K miles for the last 2 or three months. Up in 4th gear a slight acceleration will cause what seems to be the transmission to slip. If I back off, then accelerate a little more firmly, I can get it to downshift and it seems fine.

Took it into a neighborhood shop, and they say its a bad transmission. Quotes are $2870 for a used tranny, $3370 for a new one.

But they also mentioned as an aside that diagnostics showed that #5 was misfiring!

I think I'll go ahead and have them replace plugs and fuel filter to start off.

Just curious...why would the #5 misfire only manifest itself up in 4th gear?

 

That's when the mixture is leanest - the leaner the mixture, the more voltage required to fire it.

 

Had same problem, replaced plugs, which were basically non existent. And problem fixed.

 

TC locked acting like a manual, power strokes of 8 cylinders further apart due to low rpm, cylinder pressures higher .... so you feel it.

 

UPDATE!

Went ahead and took the truck into the local Ford dealership for plug replacement (had them replace the fuel filter while they were at it), and - presto! - no more "transmission slippage"! Running like a champ again. I guess at 160K miles, I got my use out of those original plugs.

So glad there are forums like this one where information can be easily shared. Without it, I'd be picking up my truck today with a brand new transmission, $3000 lighter in the wallet, only to find *nothing* had changed. Ain't the internet grand?

It wasn't cheap - roughly $600 for parts and labor. Amazingly, they didn't break a single plug removing them. They had quoted an extra $50 for each that would have broke.

Thanks again!

 

Good deal. Glad you got it fixed, saved money, and the site was of assistance.

 

Little late to the party but sounds lime a misfire

FWIW. If the trans is actually slipping the RPMS should jump way up with no acceleration at all, possibly also accompanied by a squealing noise