Hi. I'm new to the board, but I have a problem that I hope someone can help me with. I have an F150 4.6L supercab. I have 143,000 miles on it and haven't had too many problems with it until recently. When I am driving and I have the heat/ac/def on, my truck seems like its shifting in and out of gear. Not hard, but looking at the tach go from 2200 rpms at 75 mph to 2600 rpms and feeling a little "surge". I've taken it into the dealership several times and they can't find anything wrong with it. The check engine light isn't coming on. Its perplexing to me. I hope that someone has had a similar problem ( I know that sounds bad) and can help me figure it out. Sorry this is so long. Any help will be appreciated. I've looked through the boards and I can't find anyone else who's had this problem. Thanks in advance....Gerry

 

Gerry, I'm guessing you have an automatic. If you haven't done so change the tranny fluid and filter. Sounds to me like your torque converter lockup is unlocking for some reason. You should change your tranny oil and filter at the latest 30k miles. Once the fluid gets too hot and burns it degrades and then the tranny performance suffers.

After I changed my exhaust to a 3" and replaced the factory T with a flowmaster y-pipe I noticed mine holds high gear longer before downshifting as it's probably putting out a bit more torque.

Anyhow, if you want to change your tranny oil check my how-to.
http://members.shaw.ca/pferlow/transmission_oil.htm

For more reading check out my recent new thread in the transmission section: 4R70W transmission buildup articles which makes for good reading. Lots of information on how to make your tranny last a long time and some do's and don'ts.

 

Thanks for the information and the links. I did have the tranny flushed about 15,000 miles ago. Fuel system cleaned as well. One thing that I forgot to mention was that when I turn my heat/ac/def off, after a few minutes (about 5) it settles down and the surging goes away. If I turn it on again sometimes it comes back, sometimes not. I'm going to check my vacuum hoses first and then check my plugs. The last time they were out was around 110,000 mileswhen I took it in to have the 100,000 mile tune up on it. I'll also probably check out the egr valve and the MAF, TPS. Just trying to narrow it down. the least expensive way. Thanks for the help. Any other comments would be greatly appreciated....Gerry

 

One more point to note is if you had the tranny flushed and they didn't remove the tranny pan then you've got the old filter in there as well as a bunch of metal sludge on the pan magnet. The pan gasket is reuseable in case you decide to change oil and filter.

If you're on a flat road going steady-state speed the torque converter in my truck locks up in high gear around 40+ mph. I have a 3.55LS rear end. Above that speed unless you're accelerating the torque converter should stay locked.

 

I have had the same problem on all 3 of my ford trucks. For whatever reason, my motors always drop rpms when I turn the heat on...not the fan, but just the heat/ ac, etc. Incidently, I never noticed a drop when I turn my lights on in a ford...but i do other makes. I never noticed it while driving, though.

 

gdruss
just a thought, but when the heater/ac/defrost are in operation the compressor for the ac engages and disengages. had a friend ('98 F250) who experienced this not long before he had to replace his compressor(bad bearing). as a test, maybe try unpluging the electrical conection for the clutch on the compressor and run your heat and defrost--see if maybe this helps

good luck conner