hard shifts. vss?
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Senior User
Joined: Apr 2011
Posts: 104
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From: pittsburgh pa
hard shifts. vss?
Hey everyone. I have a 94 f150 5.0 a4od 4x4. I'm having a hard shift issue. What happens isit shifts fine around town. The problem starts when I drive at highway speeds for any length of time. Around 55mph the speedo starts to jump around then it starts shifting hard. Shifts really hard 1st to 2nd and also drops hard into drive and reverse. Disconnect the battery for ten minutes and its fine again until I have it at highway speeds again. I changed what napa calles the the abs sensor one the diff but that didn't fix it. Is there another sensor? It looks like there is one on the side of the tcase. If so what is it called? This is driving me nuts any help would be great.
Cargo Master
Joined: Mar 2007
Posts: 2,935
Likes: 34
From: Arcadia, Fla
Does the OD light blink when the hard shifting happens? On my 95 E350 bus, it hard shifted and the OD was blinking, I found the PSOM had a leaking capacitor in it causing the circut board to be dammaged. For me as I am a electronics tech, I fixed the problem, but for you, its best to replace the PSOM and have it reprogrammed for your truck tire size.
Fleet Owner
Joined: Aug 2005
Posts: 23,667
Likes: 301
From: Easton,Ks
Programmable Speedometer/Odometer Module (PSOM): A module that processes vehicle speed information for use in various electronic systems. The PSOM can be programmed to accommodate various tire and axle combinations.
PSOM:
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PSOM:
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Cargo Master
Joined: Mar 2007
Posts: 2,935
Likes: 34
From: Arcadia, Fla
Another test you can do if you have cruse control installed, does it work and hold speed?
The PSOM takes the rear axle speed sensor and converts it to a 8000(may be 4000 brain fart on that) pulse per mile(PPM) square wave and sends it to the ECU and cruse control modual. Probly best to pull codes now and see what the ECU is detecting.
By the way, in Subford's photo, the infamous capacitor is the silver can(with X on top) next to the plug, top left. IF that cap leaks acid out, that area will turn green goo and then the PSOM will not send out the 8000 PPM signal to the rest of the system.
The PSOM takes the rear axle speed sensor and converts it to a 8000(may be 4000 brain fart on that) pulse per mile(PPM) square wave and sends it to the ECU and cruse control modual. Probly best to pull codes now and see what the ECU is detecting.
By the way, in Subford's photo, the infamous capacitor is the silver can(with X on top) next to the plug, top left. IF that cap leaks acid out, that area will turn green goo and then the PSOM will not send out the 8000 PPM signal to the rest of the system.
Fleet Owner
Joined: Aug 2005
Posts: 23,667
Likes: 301
From: Easton,Ks
These photos should tell you the location.
NOTE:
Only wiring harness end of connector is to be probed.
Connect Digital Volt-Ohmmeter to Pin 4 (speed in +) and Pin 5 (speed in -).
Does the voltage increase smoothly and continuously from 0 to approximately 3.5 volts as vehicle speed increases from 0 to 48 km/h (0 to 30 mph)?
OR,
If available, a frequency counter may be connected to Pin 4 (Speed in +) and Pin 5 (Speed in -).
Does the displayed frequency of the signal increase smoothly and continuously from 0 to approximately 667 Hz at approximately 48 km/h (30 mph)?
OR,
If neither a voltmeter nor frequency counter is available, vehicle speed control may be used as a good indicator. If it works normally, then the speedometer module is at least receiving a speed input signal and the wiring and sensor can be assumed to be good.
/
NOTE:
Only wiring harness end of connector is to be probed.
Connect Digital Volt-Ohmmeter to Pin 4 (speed in +) and Pin 5 (speed in -).
Does the voltage increase smoothly and continuously from 0 to approximately 3.5 volts as vehicle speed increases from 0 to 48 km/h (0 to 30 mph)?
OR,
If available, a frequency counter may be connected to Pin 4 (Speed in +) and Pin 5 (Speed in -).
Does the displayed frequency of the signal increase smoothly and continuously from 0 to approximately 667 Hz at approximately 48 km/h (30 mph)?
OR,
If neither a voltmeter nor frequency counter is available, vehicle speed control may be used as a good indicator. If it works normally, then the speedometer module is at least receiving a speed input signal and the wiring and sensor can be assumed to be good.
/
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Senior User
Joined: Apr 2011
Posts: 104
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From: pittsburgh pa
No the cruise doesn't work. Thanks for the help I was lost. I'm gonna look into a new psom and see if thatfixes it. I'll post when I get it done
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Senior User
Joined: Nov 2004
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From: Indianapolis
The situation describe is identical to my experience 2 years ago after I purchased my 1993 F150. Here is the thread.https://www.ford-trucks.com/forums/8...h-a-twist.html
If your problem is not resolved as yet, you might take a look at changing the fluid.
If your problem is not resolved as yet, you might take a look at changing the fluid.
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