nix_ELFairmont

I recently noticed that the that my speed alert that is set at 120 goes off when the pin on the speedo is actually reading at about 127.

Also with cruise control set at 118 down the highway, reseting my average speed gave me an average speed of about 112.

Which one should i believe (if either)?

YOOT

Welcome to the Forums Nix!

Any one have any ideas?

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!Gn|T|0n

I wouldn't be concerned with the speed average too much; it is nothing more than an estimate despite the fact that if you reset it at a certain speed and maintain that speed, you'd expect it to average that speed. It may be a calibration problem. Unfortunately I can't really suggest how you go about rectifying this. The instrument cluster, body computer and trip computer / clock are all connected by a white striped black cable. The trip computer shares a separate connection to the body computer, a separate shielded connection to the instrument cluster and a separate earth. Perhaps check that the earth is ok (probably not your problem). Failing that, try getting the EEC checked for fault codes. Perhaps something like code 452 "Intermittent or missing speedo signal". If it is speedo related, you may notice a difference with your speed sensitive power steering ??? Have you asked Ford?

DOA

That is normal, as the speedo is designed to over read by about six kph at 100 kph, (at least that was the case in the E-series dash).

The trip computer works off the module pulses and computer and is more accurate. It will give a instant speed when reset
The VDO speed alert system works off the same sources as the trip computer.

Believe the trip computer and speed alert as its more accurate but drive off the speedo. It will allow a margin for speed cameras and radars that may just and has probably saved me a few times.

For those people with x police vehicles, be very carfull as the speedo is designed to underread. All these errors are there to ensure when you booked for speeding, your definitely speeding.

Source: retired VDO employee.

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Ford Doctor. Who requires a transfusion?

YOOT

I'm going to have to try this in my ED!

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!Gn|T|0n

Guys, I'm getting a power run on the dyno tomorrow morning, can they easily do a speedo accuracy check for me at the same time? If so, how much do they typically charge for this?