Problem with Bts

[MadDiesel73]

What would cause the trans to not want to downshift when going wot. At higher speeds over 35-40 mph . I'll be lugging at 40 mph and go to go and it doesnt downshift. Then at lower speeds 20-30 mph it downshifts but doesn't lock the converter all I get is slip.. Not good.

 

[pilot4life]

Any other changes around this time?

 

[MadDiesel73]

gears and truetrac about 1000 miles ago / 4 weeks ago.

batmowheel/new 38r/1.15 housing about 700 miles ago / 3 weeks ago.

degreased engine twice in the past 2 weeks to test for boost leaks and find oil leaks.

 

[MadDiesel73]

i ordered a blackstone test kit to have the transmission fluid analized.. the trans is only 4 months old.

 

[Derek@Vision Diesel]

Really sounds like a tuning issue on the downshifting to me.

As far as the lower speeds, the tuning also decides when the TC locks.

But if you havent touched that and it just randomly started, that is confusing!

 

[MadDiesel73]

i have 2 ts chips 1 with cales tunes and 1 with swamps tunes. i tried both chips and pretty much all the tunes are not downshifting like there suppose to. like on the hwy just a couple miniutes ago i had to slow down to 45mph and i was still in od and went to pass this guy and it wouldnt downshift. i had to go down to 35 before it would downshift by giving it fuel.

or at 55 in od if i put it to the floor is doesnt downshift it wants to lug through OD


i forgot to mention the OD off light was flashing for a few mins i had to turn the truck off then back on and it was out.


i think ive noticed is it seems to be fine when its cold. it starts acting funny after it gets hot.

 

[Groomzybanshee]

Check your trouble codes...

 

[Dieselboy.]

Check your codes ?

Is that the only problem ? Could be a bad sensor vss or mlps or even a tps sensor. The pcm might not be seeing the right voltage required to command a downshift.

Can you manually downshift ?

I'd pull your codes and call Brian.

 

[MadDiesel73]

Code was p0781 1-2 shift fault

 

[Charles]

I would first suspect that your PCM isn't commanding the shifts.

If you have KNOWN programs that acted a certain way forever, and then all of a sudden the trans stopped downshifting at the same points...

Then I would suspect that the PCM thinks you're going faster than you really are. Does the ford PCM use the sensor in the trans for shift strategy? If so, that speed sensor might be wrong, throwing everything off with it.

If you command a downshift yourself with the OD button, does it immediately shift down?

If so, it's not the trans.

 

[MadDiesel73]

I think the speed senso in the rear and the throttle position sensor play roles in shifting.

 

[Dieselboy.]

Speedo is taken from the rear end. And the OSS I believe.

Again if you manually shift it does it downshift ?

And that code is completely different then not downshifting.

 

[MadDiesel73]

yes if i hit the button it downshifts

 

[Dockboy]

A simple phone call...

870-422-(FORD)3673

Just saying...

 

[MadDiesel73]

Craig(MPD) and I talked to Brian today. were going to try a few things. shift solenoid / tq converter solenoid and changing something in the valve body along with a fluid flush.

wanted to see if anyone had any other ideas. im going to mention the speed sensor and throttle position.

 

[Charles]

Craig(MPD) and I talked to Brian today. were going to try a few things. shift solenoid / tq converter solenoid and changing something in the valve body along with a fluid flush.

wanted to see if anyone had any other ideas. im going to mention the speed sensor and throttle position.

If you push the button and the truck immediately downshifts, then there is OBVIOUSLY nothing wrong with the trans.

The PCM is simply not commanding a downshift otherwise because it doesn't think you want one. This could be low tps voltage, or a speed sensor giving the PCM a high reading, either of which would preclude the PCM from commanding a downshift.

When you push the button you are overriding all this and telling the PCM that you want a downshift, no matter the conditions. If it's immidiately doing it, then what else do you expect it to do???

 

[MadDiesel73]

I'll talk to Brian, thanks chuck.

I can't find my damn AE connector or I would see what the sensors are doing. Maybe Craig can look with his fancy snapon scanner.

 

[jngreen]

Another sensor to check would be the map sensor, if the pcm is not seeing boost (or load on engine) then it will shift according to speed and maybe by throttle position only. It will shift by default precalculated values.

 

[MadDiesel73]

I talked to Brian again. Going to look into all the sensors (speed sensors, Mps sensor, connectors, throttle position for adjustable pedals) and also the alrenators. Apparently if one of the alternators is feeding back into the electrical system
It can mess with all the sensors.

 

[Dieselboy.]

How would you test your alternators for feedback ?