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Discussion Starter #1
Heya -

Occasionally I'll be driving them the speedo & RPM will fly up - like max.. For only a second. I've only seen it as like 10-30 MPH. You can feel it a bit in the truck. What's this from? Belt slipping? No CELs

95 EFI XLT 351W

Addicted to Junk
85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
12,346 Posts
Do the rpms actually rise, or does the tach just say it rises?

If the rpms dont actually rise, my first thought would be the PSOM (gauge cluster).

If the engine rpms actually go up, then i suspect the EEC or associated sensors like the IAC. But im no EFI guru, far from it in fact.

Super Moderator
25,001 Posts
Yo Denver,
Is the ABS BULB LIT when situation occurs?
Our 96 started fluttering, then went completely bonkers; needle waved all over the place, odometer stopped reading mileage and tranny went nuts; fuel injectors were shut down momentarily; ABS light lit.
I went through all the diagnostics in the EVTM/PCED...
Couldn't read the 4WABS Code by Self-Test method either.
It was a toasted 4WABS Control Module (also called 4WABS Controller, Computer, etc.); went through 2 4WABS Control Modules at yards, both were bad too; jumpered VSS to PSOM directly at the 4WABS Control Module harness

One possibility, although MPH is off,
Pointer Waiver TSB 96-21-11 for 92-96; "...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..."
"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 year 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 Powertrain/Drivetrain Service Manual, Section 05-02A or 05-02D, to find cause and repair as needed.
  • If all items listed above check good, replace the Instrument Cluster Assembly."
Source: by Ford
But of course, we wont replace cluster.

PSOM & Odometer Not Working & E4OD Harsh Shift TSB 94-09-12 for 94 Bronco & F Series; "...PSOM (Programmable Speedometer/Odometer Module) may be inoperative or not function properly and the #8 fuse may be blown. In addition, if the vehicle is equipped with an E4OD transmission, it may exhibit a harsh shift. These conditions may be caused by trim screws installed through the 17K745 visor wire between the left hand "A" pillar and the left hand visor bullet connector..."
Source: by Ford

Following from 1996 Bronco Workshop Manual:
  • Refer to Speedometer Calibration Tolerance Specifications table under Specifications in this section. Be sure to check the odometer calibration. If both the odometer and speedometer are incorrect in the same direction, it is usually a sign that the conversion constant, tire size, or speed sensor ring are different than programmed. A speedometer inaccurate with an accurate odometer is usually a problem with the speedometer module itself.
Are speedometer and odometer calibration within specified limits?
Speedometer normal.GO to F2.
Does ERROR 3 message alternate with normal odometer display?
GO to F5. RESET conversion constant.GO to F3.
Are tires the same size on opposite ends of a common axle and properly inflated?
DETERMINE conversion constant. GO to F4.CORRECT condition or ADVISE customer. GO to F1.
  • Check tire size and type or vehicle rear axle.
  • Check whether the conversion constant in the speedometer is co rrect with the following procedure:
    • Press and hold the RESET button on the front of the speedometer while turning the key to RUN.
    • Release the RESET button. The pointer will prove out and some codes will appear on the odometer display. If an E is on the left side of the display, the module is programmed for English display mode and should have English graphics (mph). A lower case "o" signifies an overseas (metric) graphics (kph). Verify the graphics and display modes agree. (The number appearing after the type is the microprocessor revision level and is not used in this test.)
    • Press and release the RESET button again. The conversion constant and the word CAL will be shown on the odometer display.
    • Verify the programmed conversion constant is the same as that displayed on the chart. Refer to Conversion Constants Charts under Specifications in this section.
    • Key off.

Is the programmed conversion constant the same as that displayed on the chart and does the programmed display mode match the speedometer graphics?
REPLACE instrument cluster as described in this section. VERIFY proper operation.If conversion constant is wrong and programmed display mode OK, RESET conversion constant. REFER to Reset Conversion Constant in F5.
If conversion constant is OK and programmed display mode wrong, REPLACE instrument cluster as described in this section. VERIFY proper operation.
  • NOTE: The module can only be reprogrammed six (6) times.
    Reprogram speed conversion constant using the following procedure:
    • Locate the dealer mode programming enable single-terminal connector. The connector is located at the bottom of the instrument panel below the center of the glove box. On all vehicles, the dealer mode enable wire is Circuit 567 (LB/Y).
    • Insert metal clip in service wire panel connector. Clip other end to vehicle ground while the key is in the OFF position.
    • Key to RUN while holding down the trip odometer RESET button on speedometer. Release RESET button.
    • Speedometer will prove out (sweep across dial and back). The English/Metric and revision levels will be displayed. The last number of the display is the dealer mode programming lockout count. This count shows the number of allowable conversion constant changes remaining. When the count is zero (0), no additional changes can be made to this instrument cluster. If a conversion constant change is required, a service instrument cluster must be ordered.
    • Press and release RESET button again and PSOM conversion constant (without the decimal point) followed by the word CAL will be displayed.
    • Press and release the odometer SELECT button as many times as necessary to change conversion constant to the correct value.
    • NOTE: Pressing and releasing the RESET button to lock in the new conversion constant reduces the number of times the PSOM can be reprogrammed by one count. The module can only be reprogrammed six times. If you change your mind and want to go back to the old conversion constant, turn the key off before you lock in the new constant.

    • When the correct new value is displayed in odometer window, press and release the RESET button to lock in the new conversion constant.
    • Key off. Remove the ground wire. Verify proper speedometer operation.

    • Actual Speedometer or Odometer Value Indicated​
      48 km/h (30 mph) Actual Speed​
      97 km/h (60 mph) Actual Speed​
      Odometer Measure Over Actual 16.1 km Distance (10 miles)​
      Allowable Range​
      45-55 km/h (28-34 mph)​
      93-108 km/h (58-67 mph)​
      15.4-16.6 km (9.6-10.3 mph)​
Is conversion constant now set to the desired value?
Procedure complete.GO to F4.
Inspect Ground G201 in driver kick panel and
G100 @ LH front of engine compartment on upper radiator support
  • Tachometer Not Reflecting Engine Speed, Gasoline Engine
  • Circuit.
  • Sensor.
  • Check fuse.
Is fuse blown?
REPLACE fuse. If fuse blows again, CHECK for short in circuit.GO to L2.
  • Check for loose wiring connections in engine compartment or at instrument cluster.
Are connections loose?
SECURE loose connections.GO to L3.
  • Inspect instrument cluster printed circuit for damage, poor connections, or open circuits.
Is instrument cluster printed circuit open or damaged?
REPLACE instrument cluster.GO to L4.
  • CAUTION: Before checking the continuity of any circuit, make sure there is no voltage present in the circuit prior to switching the test equipment to the resistance function to avoid damage to equipment. Refer to the equipment user's manual for additional information.
  • Remove instrument cluster and make resistance and voltage checks (using Rotunda 88 Digital Multimeter 105-00053 or equivalent) at 14401 wiring harness connector as follows:
    • Check Pin No. 3 (Connector 1) resistance to chassis ground — should read 1 ohm or less.
    • Check Pin No. 10 (Connector 1) resistance to chassis ground — should read 1 ohm or less, if vehicle has 8-cylinder engine. Open circuit if 6-cylinder engine.
    • Check Pin No. 9 (Connector 1) resistance to negative terminal of ignition coil should be 1 ohm or less.
    • CAUTION: Make sure multimeter is in the voltage function and not in the resistance function to avoid damage to multimeter.
    • Connect battery. Key to RUN. Check for +12 volts at Pin No. 13 (Connector 1). Turn ignition OFF. Disconnect battery.
Are resistances/voltages within specifications?
Condition is not in tachometer. SERVICE wiring.REPLACE tachometer.
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