I hopped in my truck this morning to head to work and noticed that it was shifting real slow and lagging but it was shifting fine and nothing was slipping. I drive with OD off because 35's and 3.55 gears have a heck of a time trying to work together. Well on my way home when I started my truck and took off out of the parking lot I noticed that when it normally revs up to about 2500-3000 rpms and shifts it was now at like 4000 and shifting really really slow and not firm like it normally does. I thought nothing major of it and figured I would look into it when I got home. Went to get on the interstate and put it to the floor as it went to down shift from 3rd to 2nd it revved to like 5500 RPM and wouldnt shift down into 2nd. but once I let off the gas it would go back into 3rd and drive just fine. driving around town and coming to stop lights it will go down all the gears but going down from 3rd to second its like it goes into nuetral. From what Ive read OD is 4th gear and OD off is 3rd gear. It will shift in and out of OD just fine. Ive done some research and come up with nothing. Anybody had or heard of this problem? 99 F150, 4.6L, 2wd with 165xxx miles.

 

Faulty ECT Sensor or Tranny Fluid Temperature Sensor.

Does it shift the same way when the engine & tranny is cold?

 

Hot or cold it shifts the same way. I drove it around town to try to do some troubleshooting and got about 5 miles down the road and it was like nothing had happened at all. The truck ran perfect. I would still like to change any faulty sensors to keep it from happening again.

 

Sounds like your TPS is slightly malfunctioning.


It should shift differently when cold and when hot. It's either there is a leak in your cooling system, Thermostat is sticking slightly open, Coolant Cap not holding enough pressure or faulty sensor.

Start by flushing your cooling system. Replace the Coolant Cap, Thermostat, ECT & IAT sensor.

 

Thanks! I'll try replacing some of these and doing some tests. I haven't been able to make it do it again so hopefully it won't.