vss
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Junior User
Joined: Jul 2014
Posts: 75
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From: Lithia fl
vss
94 f 250 4x4 auto 351w
So i replaced the VSS on the rear axle. Im a little confused because now the spedo jumps around the same of more. the tranny was going into limp mode and shifting like a damn drag truck. how do i go about finding the cause. whats the procedure to get codes from the tranny, are there codes for the tranny?
p.s. i drove from tampa to orlando monday it started to flash 10 miles b4 orlando. then went away from the 1.5 blocks off I-4 to the parking lot. drove home an it never cam on. fluid looks great, right leval, no smell.
thanks guys,
So i replaced the VSS on the rear axle. Im a little confused because now the spedo jumps around the same of more. the tranny was going into limp mode and shifting like a damn drag truck. how do i go about finding the cause. whats the procedure to get codes from the tranny, are there codes for the tranny?
p.s. i drove from tampa to orlando monday it started to flash 10 miles b4 orlando. then went away from the 1.5 blocks off I-4 to the parking lot. drove home an it never cam on. fluid looks great, right leval, no smell.
thanks guys,
Fleet Owner
Joined: Oct 2005
Posts: 20,780
Likes: 1,746
From: Kentucky
Put the old VSS back in. Many of the aftermarket versions are junk right out of the box.
When you removed the old one was there a build up of grease/metal shavings on it?
Codes: Warm up the truck then do this: How to run a self test
3 Digit Code Definitions
Or purchase one of these:
When you removed the old one was there a build up of grease/metal shavings on it?
Codes: Warm up the truck then do this: How to run a self test
3 Digit Code Definitions
Or purchase one of these:
Thread Starter
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Junior User
Joined: Jul 2014
Posts: 75
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From: Lithia fl
thanks rla2005. I was not sure if it was the standard test or different. I am going to check it tonight.
And yes there was a little grease type buildup on the censer. i guess ill put her back in. say it is bad whats the best one to get?
And yes there was a little grease type buildup on the censer. i guess ill put her back in. say it is bad whats the best one to get?
Fleet Owner
Joined: Aug 2005
Posts: 23,666
Likes: 301
From: Easton,Ks
If you need to get any replacement VSS get a Motorcraft one from a Ford dealer as there are different ones for different trucks. Auto part stores try to sell a one fits all.
Getting the codes are OK for this but the code you will get will be a bad VSS input to the computer from the PSOM module.
/
Getting the codes are OK for this but the code you will get will be a bad VSS input to the computer from the PSOM module.
/
Mountain Pass
Joined: Jul 2014
Posts: 244
Likes: 0
From: Minneapolis & Terlingua
Randy...what would it mean if there was grease and metal shavings on the old VSS?
I ask because the one that I just changed out had shavings/grease.
Thanks.
Fleet Owner
Joined: Oct 2005
Posts: 20,780
Likes: 1,746
From: Kentucky
I agree with Bill. If there is more than a light coating of grease/metal particles something bigger is going on.
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Junior User
Joined: Jul 2014
Posts: 75
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From: Lithia fl
oh man. I am trying to pull codes at work today to see whats there but I dont think its guna happen. I called ford for the correct VSS its like $53. little more than the $23 from the corner parts house. can yall provide your favorit/ best
link to the stick conversion
. i may just start rebuilding the truck now.
thanks guys.
link to the stick conversion
. i may just start rebuilding the truck now.thanks guys.
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Thread Starter
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Junior User
Joined: Jul 2014
Posts: 75
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From: Lithia fl
No its ok. I was told to try this first. now it seams like i need to clean it up, pull out the diff fluid (good move dont know the last time PO did this) and put new fluid in. and put cleaned up VSS back in
Fleet Owner
Joined: Aug 2005
Posts: 23,666
Likes: 301
From: Easton,Ks
You say the speedometer is jumping and that would mean the VSS is OK.
The three main things that make a speedometer jump as you know are the rear end (bad bearings or loose tone ring or buildup on the VSS), PSOM & a bad RABS module loading the VSS signal down.
Of course there are other remote causes that do not happen as much as loose fuses, bad grounds and bad wiring.
The VSS either works or it does not it just consists of a permanent magnet, a ferromagnetic pole piece, a pickup coil, and a rotating toothed wheel. No moving parts.
As the tone wheel teeth of the rotating tone wheel pass by the face of the magnet, the amount of magnetic flux passing through the magnet and consequently the coil varies. When the tone wheel tooth is close to the sensor, the flux is at a maximum. When the tooth is further away, the flux drops off. The moving target results in a time-varying flux that induces a proportional voltage in the coil. Subsequent electronics (PSOM & RABS module) are then used to process this signal. The PSOM then drives the Speedometer, updates the mileage in the LCD odometer display and the EEPROM and sends a digital waveform to the Speed Control and the PCM Computer.
The three main things that make a speedometer jump as you know are the rear end (bad bearings or loose tone ring or buildup on the VSS), PSOM & a bad RABS module loading the VSS signal down.
Of course there are other remote causes that do not happen as much as loose fuses, bad grounds and bad wiring.
The VSS either works or it does not it just consists of a permanent magnet, a ferromagnetic pole piece, a pickup coil, and a rotating toothed wheel. No moving parts.
As the tone wheel teeth of the rotating tone wheel pass by the face of the magnet, the amount of magnetic flux passing through the magnet and consequently the coil varies. When the tone wheel tooth is close to the sensor, the flux is at a maximum. When the tooth is further away, the flux drops off. The moving target results in a time-varying flux that induces a proportional voltage in the coil. Subsequent electronics (PSOM & RABS module) are then used to process this signal. The PSOM then drives the Speedometer, updates the mileage in the LCD odometer display and the EEPROM and sends a digital waveform to the Speed Control and the PCM Computer.
Mountain Pass
Joined: Jul 2014
Posts: 244
Likes: 0
From: Minneapolis & Terlingua
If you need to get any replacement VSS get a Motorcraft one from a Ford dealer as there are different ones for different trucks. Auto part stores try to sell a one fits all.
Getting the codes are OK for this but the code you will get will be a bad VSS input to the computer from the PSOM module.
/
Getting the codes are OK for this but the code you will get will be a bad VSS input to the computer from the PSOM module.
/
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