yo Str82zer0,
WELCOME!
Note that SuperMotors.net is temp down so some links may not work..
Before buying any parts;
This problem could be caused by a # of thangs;
bad vehicle speed sensor (VSS) (also called ABS,, DSS sensor) on da 8.8 (rear differential)/ or Connector/corroded wires inside connector;
bad wiring/shorts /connectors from VSS at firewall, at 4WABS Module and /or at PSOM and then onto the PCM
bad 4WABS Module - It is located below ws wiper fluid/coolant recovery tank. So, the connector can be corroded by leaking fluid
cruddy/damaged tone ring in the 8.8.
bad PSOM (Speedo)
Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19
The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test.
Run it around to heat the engine up and shift thru all gears incl Reverse. Then turn off all accessories/lights, etc.
Make sure A/C is off and transmission is in Park (automatic) or in Neutral for a Manual & release clutch.
Do Key On Engine Off (KOEO) portion first.
Look Codes up in my broncolinks.com site using the new Search function.
And Post em here according to:
KOEO
&
KOER
Here is ONLY a SHORT EXCERPT of the Pin-Point Testing Process by Ford;
Check Fuses 8 & 18 in Cab fuse block (lower left of dash by driver's left knee)
If no 12 v on Supply Side of each; look in Power Distribution Box (Located under the hood on the drivers side fenderwell, on driver's side of the air cleaner housing)
and check **** FUSES J & S
Fuse Block Diagram in a 94 Bronco & F-Series
http://www.supermotors.net/getfile/834106/thumbnail/fuses94gas.jpg
Source: by Ford via Steve83 (Steve, That dirty old truck) at SuperMotors.net = to your year
My 96's same symptoms were erratic until the 4WABS Module's microprocessors finally burnt-out. I had one go bad and 2 yard Modules were also bad; so I jumpered the Module out as Steve & Turbo Ghost describes below.
4WABS Control Module Removal in 93-96; "...Disconnect the plug from it, remove the 10mm bolt holding it in and slide it out of the keyway" Source: by Froggmann (Ken P)
To bypass the 4WABS module @ it's harness's connector & feed the ABS signal directly to the PSOM,
Disconnect module (under coolant recovery /ws washer tank) & in connector, jumper LG/Bk to LG/Y, and R/Pk to O/LB..."
a pic of the connector and jumpers; Continuity Test Through 4WABS Module Connector in 93-96
by Turbo Ghost
Speed Input Signal Test @ PSOM in 93-96 Bronco; "...NOTE: Only wiring harness end of connector is to be probed. * Connect Rotunda Digital Volt-Ohmmeter 014-00407 or equivalent 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 & tone ring can be assumed to be good.
This is tuff to do; suggest using str8 pins to back probe the connector
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For reference purposes:
PSOM Pointer PSOM Pointer Waiver TSB 96-21-11 for 92-96; "..The speedometer needle may waver and or a light surge may occur on some vehicles..." read more
Source: by Ford
This also addresses the tone ring & PSOM unit
EXCERPT; 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.
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"). 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
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Tone Ring Inspection; "Take off the rear diff cover. Check the Ring Tone gear. It is located on the left hand side of the ring gear. Look to see if any of the teeth have been notched (from debris floating around in the diff.) Usually a spider gear. If the ring tone gear has been notched, it will need to be replaced to fix your speedo reading. Jack it up and rotate the tires to look for the teeth to be notched/broken/bent..."
Source: by Bighibbi at FSB
Tone Ring Damage pics in a 95 8.8
Source: by sackman9975 (Scott) at
http://www.supermotors.net/registry/19344/67582
more VSS info in my site @
http://www.broncolinks.com/index.php?index=139
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More 4WABS Info, Connector Location and pin out diagrams etc in my site @
http://www.broncolinks.com/index.php?index=240
