eratic speedo - Ford Bronco Forum
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post #1 of 5 (permalink) Old 12-13-2012, 12:14 AM Thread Starter
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eratic speedo

Been having this problem with my truck for quite sometime now, after it died out of nowhere a few years back. Floor it and it revs high and slowly picks up speed. It acts like it doesn't know what gear to be in. The speedometer is floating around after I reach about 20mph and will waver 10 - 20 mph above and under what I'm driving, at around 70 it will drop down to 20 and cause me to downshift hard. The motor is the 351 with the E4OD behind it.

The abs light was on and o/d light was blinking till I replaced the sensor on my differential, it shifted a little better at first but gradually went back to how it was acting.The wiring for the sensor isn't corroded.

I've heard that the PSOM could cause all the problems here, that that solder points weren't very well and could cause components to come lose, so my question is, is there a way to test if this is my problem and would there be a cheap way to fix it?
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post #2 of 5 (permalink) Old 12-13-2012, 01:04 AM
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Originally Posted by chkmates12 View Post
Been having this problem with my truck...
...which is WHAT??? Click this, read the WHOLE caption, and follow the instructions:

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post #3 of 5 (permalink) Old 12-13-2012, 09:29 AM
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yo chkmates12,

Today is a good day for me to guess what year range you have and if it is a Bronco; Since you mentioned E4OD along w/OD light and PSOM;
92-96, Correct?

If so,
Before buying any parts;
This problem could be caused by a # of things;

bad vehicle speed sensor (VSS) (also called ABS,, DSS sensor) on da 8.8 (rear differential)/ or Connector/corroded Terminals/wires inside connector;
or cruddy/damaged tone ring in the 8.8.
bad 4WABS Module - It is located below ws wiper fluid/coolant recovery tank. So, the connector can be corroded by leaking fluid
bad PSOM (Speedo)
bad wiring/shorts /connectors from VSS at firewall, at 4WABS Module and /or at PSOM and then onto the PCM the locations of the connectors along the path from VSS to 4WABS and up to Instr Cluster & PSOM are;

C404 VSS On rear axle sensor (A7) Terminals: 02

C205 LH rear of engine compartment, in safety wall (Fire Wall) Terminals: 24 In-Line

C202F & M LH rear of engine compartment, in safety wall (A8) Terminal: 7 In-Line

C119 LH front corner of engine compartment on 4WABS control module (E10),Terminals: 40

O/LB to:
C202F & M LH rear of engine compartment, in safety wall (A8) Terminal: 7 In-Line

C252 Programmable Speedometer/Odometer Module (PSOM), Behind top LH side of I/P, on PSOM (A7) Terminal: 12 Color: B at Pins 4

LG/Y to Splice S107 Engine control sensor harness, from C119 near T/O to G101 (G101 RH side of Radiator support); to PSOM Pin 5
C202 F and M
and spliced to Ground G100 (BK)
G100 & G104 (tied together in diagram) G100 @ LH front of engine compartment, on upper radiator support

G100 Serves Component:
Fuel Pump Module
Inertia Fuel Shutoff
Misfire Sensor
Misfire Sensor Shield
Output Shaft Speed (OSS) Sensor
Powertrain Control Module (PCM), 5.0L

From PSOM Pin 7 (GY/BK) to Splice S246 Main harness, near T/O to speed control amplifier to
C185 PK/O @ PCM 5.0L Powertrain Control Module (PCM) LH side of safety wall, on powertrain control module (PCM) (C10) Terminal: 104 Color: GY
C185, 5.8L Powertrain Control Module (PCM) LH side of safety wall, on powertrain control module (PCM) (C10) Terminal: 104 Color: GY

C185 @PCM to C202 F and M
Splice 216 to Ground G200, Instrument Cluster ground is inside passenger side kick panel

and on to C185 @ PCM PIN 58 (GY/BK) and from Pin 46 to MLPS (TR) Pin 2
Verify PCM & MLPS wiring & Pin numbers using following WIRING DIAGRAMs by Ford via Steve83
(my eyesight is fuzzy again)

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 site using the new Search function.

And Post em here according to:

More tests and info in my reply #8 @

And do what Steve suggested and soon in your profile, include your year, engine, trans, Xfer case & locking hub type (auto or manual) and any major mods such as body or suspension lift, etc. or in any question post. You'll get more accurate replies

See my partially recovered Bronco web site ...Will need to clean up dead links & add many more new links some day. Thanks to Mr. Schwim!

Last edited by miesk5; 07-27-2014 at 02:19 PM. Reason: Added Connector Path colors 27 JUL 2014
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post #4 of 5 (permalink) Old 12-13-2012, 06:04 PM
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Bronco Info: 96 Bronco (5.8 DD E4OD), 88 Bronco Mudder (Engineless), 90 F250 (Explorer 5.0 4R70W)
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pull the diff cover and check the fluid. check the toner ring. chekc for any damage whatsoever while your under there.

-----96 5.0 E4OD--------------88 5.8 C6--------------96 5.8 E4OD------
---------KIA-------------------Mud/Trail---------------Daily Driver------
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post #5 of 5 (permalink) Old 12-26-2013, 10:52 PM Thread Starter
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Sorry to bring up an old thread, but I fixed my problem with the bouncing speedometer and random shifting by replacing the abs sensor on the rear pumpkin with a dealer part, then removing the abs control module behind the glove box. Solved my problem, and glad to drive the truck comfortably now!
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