Automatic transmission excessive down shifting
Thread Starter
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Tuned
Joined: Jun 2013
Posts: 301
Likes: 13
From: Arkansas
Automatic transmission excessive down shifting
I have a 1997 F250 7.3 Diesel automatic with trans cooler. I took a trip with it pulling a camper trailer. At steady speed of 70mph on highway the transmission kept down shifting every 5 minutes or so. Wasn't increasing speed or going up hill? On way home it didn't do it near as much at first. Even climbed some small upgrade hills without it downshifting. As day went on it seamed to downshift more often. Can anyone give me some direction on how to slow or stop this? It really killed my mileage...went down to 8.5mpg. I had to be real careful not to push on the gas at all or it would downshift. Any info is helpful. At 70mph my tac was showing around 1800 rpm. Issue decreased dramatically if I dropped speed to 60-65mph.
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,725
Likes: 2,652
From: SE Florida
Replace the Manual Lever Position Sensor (MLPS.) In these years there was a problem where they would start to fail and indicate that you moved the shifter to the 2 position. That causes a downshift.
You can diagnose this if you can watch a live data stream. Watch the PRNDL data to see if it moves from drive when you have a downshift. It may only indicate it for a second or two, but that is enough to make a downshift happen.
You can diagnose this if you can watch a live data stream. Watch the PRNDL data to see if it moves from drive when you have a downshift. It may only indicate it for a second or two, but that is enough to make a downshift happen.
Thread Starter
|
Tuned
Joined: Jun 2013
Posts: 301
Likes: 13
From: Arkansas
Replace the Manual Lever Position Sensor (MLPS.) In these years there was a problem where they would start to fail and indicate that you moved the shifter to the 2 position. That causes a downshift.
You can diagnose this if you can watch a live data stream. Watch the PRNDL data to see if it moves from drive when you have a downshift. It may only indicate it for a second or two, but that is enough to make a downshift happen.
You can diagnose this if you can watch a live data stream. Watch the PRNDL data to see if it moves from drive when you have a downshift. It may only indicate it for a second or two, but that is enough to make a downshift happen.
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Thread Starter
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Tuned
Joined: Jun 2013
Posts: 301
Likes: 13
From: Arkansas
That is what my truck is doing also...but for no good reason at all it suddenly decides to downshift. If I try to kick the downshift out I will loose almost 5mph doing it. If I speed up and allow the normal shift... it will be ok for a while until I get back to the 70mph area then downshift again. about every 5 miles or so. Wondering if I'm loosing vacuum that's causing it to downshift?
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Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,725
Likes: 2,652
From: SE Florida
This doesn't have anything to do with a digital gear indicator. That's the sensor that tells the PCM where you have the shift lever.
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,725
Likes: 2,652
From: SE Florida
That is what my truck is doing also...but for no good reason at all it suddenly decides to downshift. If I try to kick the downshift out I will loose almost 5mph doing it. If I speed up and allow the normal shift... it will be ok for a while until I get back to the 70mph area then downshift again. about every 5 miles or so. Wondering if I'm loosing vacuum that's causing it to downshift?