speedometer issue

[julietwhiskey]

Hey all,

Let me premise this question: I bought this 95, 302-5.0L, mods-FIPK, the rest stock, FB in Feb 07. Tranny and transfer case was replaced about a year ago (so I was told). Lately as I drive, I get intermittent jumps on the speedometer. For instance, driving at 20mph, the speed does NOT drop below 20, but sparadically jumps quickly above 20 (i.e. 25, 35, etc-no routine pattern), but always drops back to 20. It is not a constant occurance every time I drive, but comes and goes. Nothing seems to be affected in the tranny as it shifts fine, but the cruise ctrl goes haywire when this acts up. No "check engine" light as well. I've replaced the speed sensor mounted on the rear differential (Ford part #, F85Z-2L373-AC also listed on the box BRAB-130) and checked the relays and fuses, both under the hood and below the instrument panel-all good. So appealing to more seasoned FB owners, what is the dealio?

Thanks for your input.

jw

 

[Seabronc]

Check the speed sensor connection on the rear pumpkin. It may also be a wire from the speed sensor to the dash being worn and intermittently rubbing on the frame.

God luck,

>-

 

[julietwhiskey]

Check the speed sensor connection on the rear pumpkin. It may also be a wire from the speed sensor to the dash being worn and intermittently rubbing on the frame.
God luck,

>-

I checked the new speed sensor at the rear pumpkin, took some compressed air (for computers) and cleaned the connections. The wires however seem solid, at least along the frame. they are enclosed in the black flex tubing. I have yet to check their connection at the relays and fuses. One question I do have, is could the instrument cluster be causing this problem? Diagnostically, the issue seems to not be improving.

I'll keep you updated.

j

 

[julietwhiskey]

I checked the new speed sensor at the rear pumpkin, took some compressed air (for computers) and cleaned the connections. The wires however seem solid, at least along the frame. they are enclosed in the black flex tubing. I have yet to check their connection at the relays and fuses. One question I do have, is could the instrument cluster be causing this problem? Diagnostically, the issue seems to not be improving.
I'll keep you updated.

j

Well, by process of elimination to try and solve the "jumping" speedometer, this is what I've done.

1-Replaced the Speed/ ABS Sensor on the Rear Differential

2-Checked to make sure that connection was solid.

3-Checked all relevant fuses for the speedometer and the instrument cluster.

4-traced the speed sensor cable, in the black flex tube, from along the frame to the under the hood.

5-Disconnected the negative battery cable for 15 secs to reset the computer (This was done right after a test drive when I replaced the speed sensor)

Results-still the speedometer jumps.

Now, all this seems to be left is the instrument cluster. This is a 250 or so dollar items new, so if I missed anything, please help me out.

Thoughts anyone?????

j

 

[julietwhiskey]

After searching forums for FB and 150's, I'm coming away with two different diagnostics paths. NOTE: I would love your comments on these. Personally, I tend to follow the pathway of "start from cheap and work expensive."

-->The first diagnostic path is the VSS on the rear differential, wiring to the Power Module, including the PSOM, then finishing at the Instrument Cluster. This is mainly a continuity/fuse/and component integrity check. The sources for things wrong on this path are; the sensor, wiring along the frame, connections to the fuse boxes, the PSOM going out, and lastly the instrument panel. A secondary indicator that something is wrong with the speedometer on this path is rough shifting, especially between 1 and 2.

-->The second diagnostic path is the rear differential itself. One forum (http://www.ford-trucks.com/forums/14544-po...eed-sensor.html) noted that the Sensor Ring was bent a bit, causing the VSS to read errors. Thus creating the speedometer jumps.

Again, my symptoms are as follows:

1-holds a minimum (true) speed, then jumps to random speeds above the true speed, always coming back to the minimum.

2-Does this intermittently but always starts at startup. Tends to correct itself when I fully stop for a bit.

3-No check engine light

4-No rough shifting

5-Cruise Ctrl can't stay on a "set" speed when it jumps.

Attempted corrections to date:

1-replaced VSS

2-checked ALL speed sensor fuses/ relays.

3-checked and cleaned VSS connections/ wires from source to split at rear diff for ABS, and along frame to Power Module.

4-performed and passed PSOM test {You can see yours by holding the Reset button while turning the key forward to Run, then release Reset. The needle will do a full sweep test, and the odometer display will show "E ## #", meaning English units, the microprocessor revision (mine is 08), and the conversion constant lockout count (maximum is 6). Canadian ones might show "o" in the first position meaning "Overseas" (Metric) units. Pressing Reset again shows "####CAL", which is the conversion constant (without a decimal).}

5-after installation of the VSS, I unhooked the neg bat connection for 30 secs-then reconnected.

So, I'm running out of options to look at. This weekend, I will pull the rear diff cover off and look at the sensor ring for bends/ breaks. If that isn't it, then the instrument cluster can be the only other option. Is my analysis of this correct? Again, I admit I'm green at this so any wisdom from the experienced is most welcomed to a newbie.

Thanks a mil.

 

[wileec]

You have done all that I could imagine. You said this hapened at around 20MPH does it happen at hiway speed as well? If so does it matter if you coast or excelerate? (just throwing ideas in the air) could it be part of the cruise control vaccum? Have you hade cruise recall done? I would think that the cluster would not cause something like this but with electrical problems ANYTHING is possable. It seems thouhg that the cluster is just there to pass info to you it goes through the computer first. Maybe try unpluging the cluster first see if that effects the shifting at all points. If I think of anything else I wil let you know...GOOD LUCK

 

[miesk5]

yo; you have done the checks so far IAW the TSB.

The TSB (below) mentions "when speed control is used at highway speeds between 80-113 km/h (50-70 mph)."

So, I'd too go for the slight dents/chips in either the exciter ring - and air gaps between the VSS and the exciter ring

But, try one more inspection of the VSS Sensor's connector and wire strands inside connector (even tho you may have done a continuity check?); esp. bec. you wrote; "... Tends to correct itself when I fully stop for a bit." I sense this is vibration related and like you, I look @ <$ and the most likely causes... mainly electr. connections under da Bronco.

PSOM Pointer Waiver TSB 96-21-11 by Ford for 92-96

Programmable Speedometer/Odometer Module Pointer Waiver Article No. 96-21-11

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.

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 0.38-0.51 mm (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 0.1 mm (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

Bronco 962111B Replace Programmable 0.7 Hr.

BASIC PART NO. CODE 10849 06

OASIS CODES: 204000, 204100, 204200, 205000

 

[julietwhiskey]

You have done all that I could imagine. You said this hapened at around 20MPH does it happen at hiway speed as well? If so does it matter if you coast or excelerate? (just throwing ideas in the air) could it be part of the cruise control vaccum? Have you hade cruise recall done? I would think that the cluster would not cause something like this but with electrical problems ANYTHING is possable. It seems thouhg that the cluster is just there to pass info to you it goes through the computer first. Maybe try unpluging the cluster first see if that effects the shifting at all points. If I think of anything else I wil let you know...GOOD LUCK

The symptoms do suggest a loose wire like you all said. I will be crawling under the rig later today. Question on looking for loose wire: Other than something blatenly exposed, where are the touchy points to look for look wiring at. Once its in the flex tube, it would seem that its protected. I will recheck the VSS connection.

 

[mbtech2003]

STOP I HAVE YOUR ANSWER MAYBE???? the same thing was happening to my truck and the cause was the spider gears in the rear diff chipped and a piece fell off and took out a tooth from the abs tone ring in the rear end. take out the sensor and spin the rear end up on jack stands and peek down into the hole. make a complete revolution and check to make sure this has not happened to u. or u can just undo the 10 bolts for the cover of the diff to inspect. probably needs a fluid change anyway lol.

and you can inspect the gears at the same time. dont' forget to get limited slip additive if it applies to your truck.

good luck >-

 

[julietwhiskey]

STOP I HAVE YOUR ANSWER MAYBE???? the same thing was happening to my truck and the cause was the spider gears in the rear diff chipped and a piece fell off and took out a tooth from the abs tone ring in the rear end. take out the sensor and spin the rear end up on jack stands and peek down into the hole. make a complete revolution and check to make sure this has not happened to u. or u can just undo the 10 bolts for the cover of the diff to inspect. probably needs a fluid change anyway lol.and you can inspect the gears at the same time. dont' forget to get limited slip additive if it applies to your truck.

good luck >-

This is just a quick note to put a close to this topic. After all the checks and rechecks, the issue stemmed from the PSOM. Unlike most other folks in here that have the PSOM problem, as described by the Tech Report, my problem is again, a speedometer whose needle jumps at ANY speed (both below 50-70 and above). My technical solution that fixes it is....to push the "select" buttom a few times and the needle steadies. So, to save myself 180 bucks for a new PSOM, I'll let this one play finicky for a while, till the hard shifting in 1 & 2 begins and the needle jumps ONLY above 50-70.

Thanks for

 

[julietwhiskey]

This is just a quick note to put a close to this topic. After all the checks and rechecks, the issue stemmed from the PSOM. Unlike most other folks in here that have the PSOM problem, as described by the Tech Report, my problem is again, a speedometer whose needle jumps at ANY speed (both below 50-70 and above). My technical solution that fixes it is....to push the "select" buttom a few times and the needle steadies. So, to save myself 180 bucks for a new PSOM, I'll let this one play finicky for a while, till the hard shifting in 1 & 2 begins and the needle jumps ONLY above 50-70.

This reply is to close out this post. The "push the select button" method to correct the jumping speedo only worked for about a month. Also the trans started to surge in every gear, along with hard shifting, both up and down, at the shift points- especially in 3 and OD. So, I went to a junk yard and pulled the speed gauge from an instrument cluster and bought it for 50 bucks. This was a crab shoot since you cannot test it till you install it. but to my luck, it functioned fine, although I just increase 20 K miles in one day.

The options for the PSOM fix were:

1-buy it from ford (around 400 bucks I heard. I never called to verify)

2-send to dashusa.com for a replacment. The fellow there was very helpful and forthright. The price was 290 with shipping.

3-go to a junk yard and take you chances, since all of them don't give refunds on electronic components.

Since the rule of "start cheap and work expensive" reigns supreme here, that's what I did. The junk yard unit is working!

So, hopefully for this post will cover all the issues that arise from speedo jumps and PSOM's. Thanks again for everyone's advice.

jw