Ford Edge Speedometer - Only sometimes does the Customer concern occur

Ethan Educator Rapid City, South Dakota Posted   Latest  
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2008 Ford Edge Limited 3.5L (99C) 6-spd (6F50)

2008 Ford Edge with 196K Miles, Original Engine/Transmisison. Aftermarket wheel/tire assemblies (overall size equal to factory specified tire circumfrance).

Customer states the Speedometer will become erratic after extended drive time when traveling above 82MPH, both using foot pedal and cruise control. Never has it acted up if speed less than 82MPH. It will at times drop down to a lower number than actual speed traveled, and hason two occations gone to ZEROmph. The RPM guage has dropped to ZEROrpm only when the Speedometer went to ZEROmph, but Customer did not notice a change in the RPM guage when erratic speeds shown on Speedometer. Also to their knowledge all other guages worked and no lights flash or chage on Instrument Cluster. Customer lives in Montana with speed limits of 80MPH, travels between Montana and North Dakota for College Courses.

No codes found in any modules, scan tool data observed in all modules showing vehicle speed and wheel speed. The instrument panel recieves inputs via Serial Data for the Speedometer from the PCM. The vehicle has been test drove extensivly and the tech is UNABLE TO DUPLICATE the concern in any capacity. Transmission data was watched to verify shifts, torque converter slip speeds, gear ratios all correct. ECM data was watched to look for fuel and ignition issues.

Read through the D&O for cruise control, instrument panel and see nothing that gave a more distict dirction to follow since the concern was not duplicated.

Below are screen shot pictures of the only odd data found during testing. You will see that vehicle speed is at 84mph when observing the PCM transmission data. Then the Instrument Cluster shows vehicle speed registered at 34mph.

My thoughts are that the cluster has an internal issue that speratically shows itself, but I would like some input as to if anyone has seen this issue or has some data PIDS that should be more closely monitored.

Thanks

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John Diagnostician
Redlands, California
John Default
 

Check for ignition coils causing voltage spikes to the PCM. Look for misfires in mode 6 data. If you have access to a “power balance’ test such as in Ford IDS, look for misfiring cylinders under load. A lab scope can also be used. Connect to any of the coils b+ circuit and look for voltage spikes indicating a coil problem. Good luck.

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Ethan Educator
Rapid City, South Dakota
Ethan Default
 

Thank you for your reply. I have been using a Bosh scan tool and found no history or current misfires under any load ranges. I do have access to a scope and can check for stated voltage spikes on the B+ circuit of the coils. Thank you

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Maynard Technician
Elmira, Ontario
Maynard Default
   

I think it might be worth observing all wheel speed data as well to see if one is dropping down at any time, About that era the windstars had a system where they would average out the wheel speeds to gain a speedometer reading, so if one wheel speed was showing 0 the speedometer would only read half of actual vehicle speed. I dont know if this vehicle works that way, that is just something that…

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Ethan Educator
Rapid City, South Dakota
Ethan Default
 

That is good to know. I did watch the Wheel Speed Sensors for an extended time and never saw a drop. That was only utilizing a scan tool though, not with the scope. Tried to be very observant of all possible data PIDs looking for an abnormalty. The real issue is that it has not acted up for me and the sympotoms are only the customer gathered info at this time.

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Ethan Educator
Rapid City, South Dakota
Ethan Default
 

youtu​.​be/GQwDFmIkapM I am not a big fan of YouTube, but as this vehicle will not act up for us at this time and Student will be returning to college soon, wanted to do some digging for similar symptoms. This video is rather close to customer stated concerns accept the customer has not yet had complete failure with transmission going into limp mode. I am posting this as a…

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