Originally Posted by John V6
Rene,
mine under reads so 70 is 77 mph. That I understand is illegal. I beleive car speedo should show the speed with a range of -0 to +10%.
The way my car is set up is n opportunity to lose my license.

Didn't realise the 10% error was in that direction John given as you suggest, a speedo that under reads is illegal. Most over read to the tune of 5-8% as you know. Suggest having a look at the Mustang forums on this subject. A further thought is your factory modified PCM (ECU) may offer more tweaking opportunities given its the device the gearbox output sensor communicates with [Linked Image]. Indeed that PCM may be the cause of the issue, as I believe the testing Adrian (AJSki2fly) did on behalf of MMC involved such.

Last edited by Richard Wood; 17/09/20 08:33 AM.
Richard

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