Speed Signal - techies please help!

[Mark Ayling]

I wonder if anyone can explain something to me...

Firstly, my Apexi rev/speed meter has never read above 97mph - I vaguely understand that this is something to do with the way its wired in relation to either the bit which removes the speed restriction or the kmh/mph conversion?

Secondly, on occasions, I have noticed that when on the move the rev/speed meter has shown a much too low figure, ie 7mph when I'm doing 40mph or something. Seems to be alright at the moment though, so its obviously an intermittent thing - could this also be related to a dodgy conversion?

Any info appreciated!

Cheers,

Mark.

[THOR Racing]

Firstly, my Apexi rev/speed meter has never read above 97mph

99.9% likely cause is it's fitted to the ECU speed input wire which has a speed delimiter attached (clamping at 97mph)

Just move the wire to the other side of the speed delimiter or output from the odometer and it'll be fine.



Secondly, on occasions, I have noticed that when on the move the rev/speed meter has shown a much too low figure, ie 7mph when I'm doing 40mph or something. Seems to be alright at the moment though, so its obviously an intermittent thing - could this also be related to a dodgy conversion?

Odd? Intermittent things like this are unusual.
Intermittent suggests wires broken etc which would be a working/non-working situation not a MPH O.K. then MPH-7mph ???

This is compared to the speedometer reading I guess, or do you have a GPS meter?

Could be the converter (please don't say it's one of mine :( )

Some converters (not mine) just blindly remove pulses from the digital pulse train to get the 5/8ths conversion. i.e. out of every 8 pulses comming in they drop 3.
i.e. 1,2,3,4,5,6,7,8 becomes 1,2,3,4,5, , , ,1,2,3,4 etc etc

Now on average the speed in reduced by 5/8ths but in reality for a digital system counting pulses this appears to be a signal bursting on and off. This could be the error you are seeing.
Just a guess.


Regards
Pete

[Martin F]

Originally posted by TRL Performance



Odd? Intermittent things like this are unusual.
Intermittent suggests wires broken etc which would be a working/non-working situation not a MPH O.K. then MPH-7mph ???



Shall we have a wager on whether it's a Scotchlok ??

:(