Indicated Road speed goes to zero after 70mph!

[mefmotorsport]

I have a hall effect sensor on my front hub (undriven), it picks up from the rear of the 5 wheel studs.

I see the indicated speed on the X Dash via the canbus connection from the DTA S80

It works fine and is very accurate indicating mph within 1mph of the gps but when I get to about 70mph or so it just stops and drops to zero. If I then slow down it comes back on at around 15mph indicating normally.

As yet I havn't had time to take a look at the signal from the wheel sensor or even the DTA software but I cant see why there would be a problem, anyone come accross anything similar?

I saw a similar problem once before but that was due to the high frequency generated by an ABS sensor with 44 teeth that a Stack Dash couldn't handle.

Martin

[stevieturbo]

Someone posted a few days back about a very similar issue.

Was waiting for him to post a datalog, but never heard anything more.

Is it just a single wheel, or all wheels ?

I just use the GT101's on mine. Front is a cut down front Subaru ABS ring ( some teeth removed, now at 11 teeth ) and rear's just read off the disc bolts, 8 each

Ive never had any issue with readings, even over 200mph.

I did previously have 22 teeth at the front, but cut them down again after trying to fit a Dash2 to the car and 22 was too many for it, so ended up with 11. Even at 22 teeth never had any problems.

Do you have a datalog ?

[mefmotorsport]

Yes, just one front wheel at present just for road speed.

I asked Alan and he also said look at the log, I'll do that when I have time, currently busy wiring for spotlights and sorting a coolant leak on heater/demister


Cheers,

Martin

[stevieturbo]

Do you know which signal or wheel is being lost ?

[mefmotorsport]

Strangely its working perfectly on a test drive this evening!

I only have the one sensor, its on the front nearside wheel.

Oh well, not too important just now, will look into this another time after the rally this voming weekend.

Martin

[mefmotorsport]

On another road test last night the speedo started playing up again, this time when it dropped to zero I switched off the ecu then back on again, the speed immediately went back to the correct figure so I think this might be an ecu issue.

Martin

[stevieturbo]

Check the logs for any erratic readings first. Could still be wiring or sensor related

Is it always exactly 70mph ?

[mefmotorsport]

No, it's not exactly 70 or any definite speed, seems OK generally below 70 or so but once above that it goes to pieces. I cant see how it can be the wiring, why would a power reset fix that or even if the sensor was faulty?

Martin

[stevieturbo]

power off shuts down power to sensors as well. Who knows really. Intermittent faults are always a pain in the hole !! Often there is no logic as to how they occur.

What about pinning it into another wheel speed input, or pairing it into another to see what happens both on the logs ?

That would certainly rule out or highlight a problem.