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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

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Old 01-06-2002, 06:23 PM
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John7894 John7894 is offline
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Post Possible bad PSOM or speed sensor??

Hi,
Just signed up, it looks like some people here really know there stuff. Here's my problem:
1) Speedo jumps around erratically.
2) Cruise control won't lock on a speed, it wants to hunt around.
3) Tranny shifts into 2nd hard, occasionally comes out of OD at highway speeds.
4) ABS light is on on dash.
Is the PSOM or the speed sensor bad?
Does anything else sound like it is bad or needs attention?
Any help would be appreciated!!
Thanks in advance,
John B.
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Old 01-06-2002, 10:28 PM
beratte beratte is offline
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Possible bad PSOM or speed sensor??

Definetly sounds like the PSOM, I think this TSB is exactly the problem your having.

Programmable Speedometer/Odometer Module- Pointer Waver-Service Tip
Article Number 96-21-11

LIGHT TRUCK:
1992-96 AEROSTAR, BRONCO, ECONOLINE, F-150-350 SERIES

ISSUE:
The speedometer needle may waver and/or a light surge may occur on some vehicles when speed control is used at highway speeds between 80-113 km/h (50-70 mph). This may be due to slight dents/chips in either the exciter ring or the Vehicle Speed Sensor (VSS) and air gaps between the VSS and the exciter ring.

ACTION:
Replace the Programmable Speedometer/Odometer Module (PSOM) if required. New PSOM's come with increased immunity to system variability. Refer to the following Diagnostic Procedure for details.


DIAGNOSTIC PROCEDURE

BRONCO/F-SERIES - Perform normal PSOM diagnostics per Pinpoint Tests "H" and "J" of the 1996 F-Series/Bronco Body/Chassis Service Manual, Pages 13-01-30 through 13-01-32 and Pinpoint "B" of the 1996 Powertrain/Drivetrain Service Manual, Page 10-03-11.

ECONOLINE - Perform normal PSOM diagnostics per Pinpoint Tests "H" and "J" of the 1996 Econoline Body/Chassis Service Manual, Pages 13-01-29 through 13-01-31 and Pinpoint "B" of the 1996 Powertrain/Drivetrain Service Manual, Page 10-03-9.

AEROSTAR - Perform normal PSOM diagnostics per Pinpoint Test "K" of the 1994 Aerostar Body/Chassis Service Manual, Page 13-01B-31.

1. Any slight dents, chips, etc., in either the exciter ring or VSS will create needle waver. Measure air gap between the VSS and exciter ring. It should be 0.38-0.51mm (0.015-0.020").

2. Check exciter ring runout per the same ring gear backface runout procedure of the appropriate model 1996 Powertrain/Drivetrain Service Manual, Section 05-00. Make sure the exciter ring is mounted correctly to the ring gear. If runout is more than 0.1mm (0.004"), perform the differential runout check per the procedure in the appropriate model 1996 Powertrain/Drivetrain Service Manual, Section 05-02A or 05-02D, to find cause and repair as needed.

3. If all items listed above check good, replace the Instrument Cluster Assembly. Obtain the correct service part number from the Parts Catalogue and then contact the Electronic Odometer Exchange Center at (800) 259-9700 for U.S. Dealers and (800) 663-9974 for Canadian Dealers.

NOTE:
DEALERSHIP MUST TELL THE ODOMETER EXCHANGE CENTER THAT YOU NEED A PSOM3 LEVEL CLUSTER FOR A SPEEDOMETER NEEDLE WAVER CONCERN.

OTHER APPLICABLE ARTICLES: NONE

WARRANTY STATUS: Eligible Under The Provisions Of Bumper To Bumper Warranty Coverage

LABOR ALLOWANCE



DEALER CODING



OASIS CODES: 204000, 204100, 204200, 205000

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Old 01-06-2002, 10:32 PM
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Possible bad PSOM or speed sensor??

It could be a ton of different things. First off, how many miles on the truck? And it does have the 8.8" rear end, Correct? If so i'd pull your rear diff cover off and slowly spin the drive shaft by hand, Bolted to the carrier there is a speed sensing ring which runs the abs and your speedometer(your cruise runs off your speedo). The 8.8 rear end that you most likely has a tendency to go out. What can happen is that if metal pieces start breaking up and getting at that speed sensing ring it'll get the little teeth bent which sends a bad signal to your speedo, which in turn screws with both your abs and cruise. And it'll also send that screwed up signal to your tranny and cause shift problems. I know this cause what your describing happened to me about two monthes ago. I threw a speed sensor in, checked all the wiring, and almost ordered a gauge cluster and computer before my rear end locked up,,,,i figured it out when that happened. My spider gears were completely ground to nothing. As far as i could figure a piece from one of the clutch packs in the Trak-loc busted off and lodged itself between the sensor ring and the housing. One tooth was bent about a 1/16 of an inch different than the rest, but it was enough to set it off. The sensor ring was really cheap at the dealership, it was only like 20 bucks. Unfortunetly if this is the problem most likely you'll be looking at 50-600 dollars for a complete rear end rebuild. So the first thing i'd try would be to drain the rear end and check that. And even if thats not what it is, changing your diff fluid can't hurt. You can try to change that sensor on top of the housing, its about 15 bucks. Hope its the later. If you have any questions feel free to email me at Ryan50hrl(No Email Addresses In Posts!) If you do end up needing parts i have a bunch of stuff that might work for you. Gook luck
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Old 01-06-2002, 10:50 PM
PAUL_2 PAUL_2 is offline
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Possible bad PSOM or speed sensor??

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Old 09-06-2010, 07:25 PM
MIKE8349 MIKE8349 is offline
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If you ever need a PSOM rebuilt, look up southern speedometer in Clearwater, Fl -
Mine went out and they fixed it for $145 and I had it back in the next day.
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Old 08-23-2012, 11:28 PM
lindboep lindboep is offline
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PSOM Sensor

I am having the same problem on my 96 F-250....

Speedometer is bouncing
The odometer works only sometimes
ABS light is on
Check engine light flickers..

Someone said it was the PSOM sensor......Where is that located at on the truck?
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Old 08-24-2012, 10:22 AM
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Quote:
Originally Posted by lindboep View Post
I am having the same problem on my 96 F-250....

Speedometer is bouncing
The odometer works only sometimes
ABS light is on
Check engine light flickers..

Someone said it was the PSOM sensor......Where is that located at on the truck?
Post#6 in this thread: http://www.ford-trucks.com/forums/10...ng-engine.html

But it is not causing your ABS light on issue......
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Old 08-24-2012, 11:26 AM
Truckin Bob Truckin Bob is offline
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I'd double check the "ground system" for the PSOM first.

I "think" the ground for your psom is located on the firewall in the engine compartment, passenger side, up high.

That ground also has to be grounded to the fender as well as a ground wire from the battery to the fender.

At least that's how my 94' is if I remember correctly.

Any loss of ground in those places will "unground" (open circuit) the psom.

Also, check that fuse #8 and fuse #16 are seated into the fuse holder (in the cab) snugly. A loose fuse in a fuse holder will cause intermittant power.

My thoughts, maybe I'm correct,

Bob
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Last edited by Truckin Bob; 08-24-2012 at 01:07 PM. Reason: correct information given
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Old 08-24-2012, 12:53 PM
lindboep lindboep is offline
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Ok so I was also told to check the VSS sensor. Where is that? Also where is the actual psom located on the truck?
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Old 08-24-2012, 01:03 PM
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Quote:
Originally Posted by lindboep View Post
Ok so I was also told to check the VSS sensor. Where is that? Also where is the actual psom located on the truck?

The PSOM is attached to the back side of the instrument cluster. There is a photo in Post#6 of this thread: http://www.ford-trucks.com/forums/10...ng-engine.html

The Vehicle Speed Sensor (VSS) is located on top of the rear axle center section:
Click the image to open in full size.


PSOM and VSS info here: Steve83 PSOM and VSS info

Be sure to check the codes that are causing your Check Engine Light to flicker on/off. There is a code for missing or erratic VSS pulses.
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Old 08-24-2012, 03:09 PM
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So I found out today that the cruise control does work BUT only when the sooedometer is boucing. Check best. It looked fine
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Old 08-24-2012, 03:11 PM
lindboep lindboep is offline
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So I fou out today that the cruise control does work BUT only when the sooedometer is boucing. Checked vss.It looked fine. Also tried to get advance to run codes but no computer hookup? Where is it located?
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Old 08-24-2012, 03:37 PM
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The Diagnostic Link is located on the driver side inner fender, near the hood hinge:
Click the image to open in full size.

You can check for codes yourself by following this: Fuel Injection Technical Library » How To Run a Self-Test

How did you "check" the VSS? You need a meter to check the output. One of the links I sent earlier has a procedure for doing this.
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Old 08-24-2012, 08:50 PM
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Ok i take that back i check the wires....i have a digital multimeter...can i use that to check it? if so how do i do it?
I noticed it is not shifting into the last gear...no overdrive, but when im going down a hill if i shift it into neutral then back in drive the goes in a higher gear but immediately shifts back down one....also i noticed it backfires and the engine rpm is very high even when i let off the gas going down the road at 50 mph
cruise control works when the speedometer is bouncing as well as the odo works when speedometer is bouncing
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Old 08-24-2012, 10:01 PM
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Quote:
Originally Posted by lindboep View Post
Ok i take that back i check the wires....i have a digital multimeter...can i use that to check it? if so how do i do it?
I noticed it is not shifting into the last gear...no overdrive, but when im going down a hill if i shift it into neutral then back in drive the goes in a higher gear but immediately shifts back down one....also i noticed it backfires and the engine rpm is very high even when i let off the gas going down the road at 50 mph
cruise control works when the speedometer is bouncing as well as the odo works when speedometer is bouncing
In the link I posted in Post#10 there is a drawing of the VSS/Speedo circuit as well as a test procedure. The instructions have you place the DVM on the input to the PSOM.
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Old 08-24-2012, 10:01 PM
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