Hey everyone. I have a 99 F150 4x4 with a 5.4 and 4r70w with 141k miles. For the past few months, my TCC hasn't been able to unlock in 4th gear and it won't coast either like it used to. When you let off the gas, it feels like you're pulling a tandem axle truck with all the brakes locked up on it, and when you get back in the gas, the revs don't "flare" like they would when the tcc disengages. It used to be a random thing, but now it's all the time. Also, the tcc will engage and disengage in 3rd just fine.

I was wondering if anyone has a wiring diagram for the tcc's circuit (power supply, ground, switch, etc). Or, if anyone else has had this same issue if they could let me know what has cleared it up for you.

Also, extra info: has abs codes present for right front wheel speed sensor and abs pump (abs pump code present way before this happened, wheel bearing code was within the last week). It also does it's "warm up" procedure fine, where it won't lock up the converter until it has reached operating temp, and it coasts just fine when cold.

Truck also gets horrible gas mileage. It used to get about 17-19 between 55-60 mph, and now it's lucky to get 11mpg at that speed. Feels a little boggy too.

Anyone have any ideas? Any input is appreciated.

 

We need to clear up some operation first.
When the trans is cold at startup, it will not lock up the converter by design.
This is controlled by a temperature sensor on the tans valve body, so is normal.
All shift and control function decisions are made by the computer in response to the throttle position, road speed and engine RPM.
Clear up some questions; does the shifter switch unlock the OD?
Does the trans upshift all the way to OD at road speeds over 45 mph?
Will the torque convert unlock from OD with added throttle?
Will it down shift from that point above back to third gear?
Note the first unlock is about 300 rpm. The second downshift will be about 1000 rpm.
.
Have you checked for any transmission codes?
The ABS faults might have an effect on shifting if it is used to detect road speeds in your build.
If the trans lockup works at all, it's not wiring and there are no switches.
You have to understand the operation and make the checks before repairs can be made.
Good luck.

 

Yes, the shifter button does still drop it into third.
No, the clutch does not kick out with added pedal, it either lugs or drops straight into 3rd with the converter still locked.
It still has normal shift patterns and doesn't go into o/d until roughly 45 mph under light throttle. When it goes into o/d, it almost immediately locks up the converter (if the trans is up to temp) and won't unlock it until its below 41-42 mph. It seems like when its below that speed, it stays in o/d with the converter unlocked (pushing the button on the shifter will knock it down to 3rd and lock up the converter if its above ~30mph).
You can definitely feel that the trans just skips the unlock and straight drops a gear (at 45 it goes from about 1200 rpm to about 2000rpm, at 55 it goes from 1500 to ~2400). Pretty much if the truck is above 45mph in o/d, the converter is locked and will not unlock, no matter what you do.

I will get it scanned again, even though the last scan done was about a week ago. It had no transmission codes saved. Maybe i'll see if leaving it run will save a code next scan. Might be some freeze frame data that keeps getting erased or something.

 

From what your describing, everything works correctly but the response to additional throttle in OD and in Deceleration.
Unless some code appears, I would suspect the Throttle Position sensor of having a rough spot or the ABS is causing the issue.
The PCM is not detecting the change in driving your signaling it to perform.
After all the TPS, road speed and engine RPM are the only way the PCM has to know what is going on and what your intent is, by throttle position.
Otherwise it's all working as it should.
Good luck.

 

Solid info. Thanks, i'll test out the tps before work and get a scan done again.

 

Well, I tested the tps and it was smooth as silk both opening and closing, and all voltage readings were within spec (4.8v signal, closed read 0.99v and wide open read 4.76v with smooth transition). I'll still get it scanned because it seems to have an intermittent miss at idle now. I will also check wiring and pull the trans pan off (i dont know when the fluid and filter were last changed, so taking a peek can't hurt).

 

Got it scanned today.
2 tps codes (low signal)
1 communications fault code
I'm going to check the sensor again tonight or tomorrow. As for the com code, i've made an attempt at cleaning up all my chassis and body grounds along with power wires (lots of corrosion, damn salt). Under the driver's kick panel I've discovered a rust hole and some corrosion in the pigtails. I'll try to clean them as soon as I can.
This thread is more into a journal than I thought it would haha.
The guy who scanned it said my GEM was probably fubar, but I highly doubt it considering everything else works fine (windows, locks, gauges, 4wd, etc)

 

Now your getting to the cause of your issue.
Since you did not give the codes by number, I go on to say the clue is 'communications' issue.
Is that not what is exactly happening?
The PCM is not detecting your driving changes.
.
Another feature that likely is not functioning is the little known TC unlock feature.
What is supposed to happen at normal road speed in OD is a sudden lifting of the throttle position being detected and performing a TCC unlock.
If the brake pedal is not operated during a short interval, the TCC re-locks.
Why: this function is built into the software to assist in shorting the braking distance in event of a panic braking incident.
This makes the drive line soft from converter slips so the motor and the weight of the vehicle reduces an effort to slow the vehicle.
Few know this feature exist and it can be seen by observing the Tach rise in RPM then a drop as the TCC re-locks. if the brake has not been applied.
The time interval to re-lock is in the order of 5 to 10 seconds.
Good luck.

 

Well, i have some great news! I replaced the tps (rechecked with an analog meter and the voltage was jumping around) and i cleaned up some green connections in driver's side kick panel. It took a few miles for the truck to understand that i actually messed with things but now it's healthy as could be. And it seems as though each tank of fuel is getting better now! Before the tps and cleaning, the truck was averaging about 12 mpg hwy on a really good day. After the work, i took it on a trip (loaded, about 1000lbs of tools and a small trailer) i averaged 16mpg. This current tank might break 17mpg (hwy back and forth to work, empty).

Also, throttle response is right there. I guess i never realized how sickly the truck was getting. Before, it used to "blurp" before it would move. Now, you breathe on the pedal and it's going RIGHT NOW. Lol just when i was getting ready to post it up on craigslist. It would be a shame to sell it now. Thanks for the help, bluegrass! It's much appreciated!

 

Good for you.
On a forum like this we can't always see what is happening but to ask questions trying to get more info.
The TPS is a very important sensor.
1. It tells the PCM the throttle plate angle.
2. It is part of the fuel injection amounts at any given speed.
3. It's rate of change per your FOOT movement can increase fuel needed for acceleration.
4. It plays a large part in transmission shifting points both up and down.
5. It plays a key part in OD operation.
6. It can shut of fuel injection on a non running engine if operated over about 7/8th travel.
7. It tells the PCM to go full fuel richness above the same area when the engine 'is' running.
8. It has a roll in when the EGR is opened and closed in OD.
9. It tells the PCM what your doing with the throttle so it can honor your request at any given time.
10. It tells the PCM to do 'house keeping' by updating tables when the PCM has the least to keep track off during deceleration times..
And no doubt more.
So sure, not surprised there was an issue with the plug ups that interfered with all these functions.
Good luck.