MoTeC Global Forum

Gear position is doing something weard on the car i just finished, and we are at the track for the 1st contest. With the engine stoped the output voltage from the sensor is reading 3.2V with the engine runing, 2.4v and as the rpm's go up, the voltage comes down up to 1.8v. The voltage supliyes are constant, regarding any rpm, to the map and the tps is 4.92v, but to this sensor, on the aux 5v output it's 5.12v...could this cause the sensor to do something like this ? That the voltage reference is over 5v? Sensor ground is wired to sensor 0v, B15. The sensor reads corecty through gears, but if left in a certain gear, that voltage drops the same as the engine is reved. Hope to solve this out...this is the 6th M84 i've fitted on a car, and the first to have problems like this. Battery voltage is a steady 13.4v as the engine is reved. Grounds are solid, just finished the full mil-spec loom.
PS: i have just noticed this today, as the new sensor just arrived. With the old one, i have blamed the sensor...but the brand new one is doing the same.

Are you using a hall effect rotary pot for gear position, or is it a standard potentiometer? Does this happen if the sensor is not installed on the gearbox (ie, could there be a vibration or EMI issue that affects the sensor?)

Have you checked the resistant to 5V and 0V in the scenario you describe, not running, running, and RPMs increasing.

Is the terminal in the M84 connector fully seated?

Ok, i have done some research, and tried fitting a map sensor on the output and it works perfectly, so the sensor seems to be the problem. It dose the same with the sensor unpluged out of the gearbox. This Race the car will run without the sensor, with the driver lifting the gas. But i will have to make it work somehow... Any ideas? This is the sensor. Best regards, Vlad.

I would bet that sensor wiring doesn't match your vehicle wiring. Time to cut the boot off, and verify the wiring pinout.

Triple checked the wiring first thing, even do i did the wiring loom myself...Funny thing is that if the sensor is wired as it's written on it, in revers i have 3.5 volts, and in 5th 1.2...i'm thinking that is should be the other way around. If i switch the 5v with the 0v, the sensor should read normaly...from 1.2 to 3.5, like a tps, right ? and maybe that'l take care of the situation...

It's a hall sensor... it dose not work with the 5v and the 0v wires switched...so the wiring is okay....what next? I did found a loose connection in the main charging wire from the alternator(one of the mechanics). Could that be the source of the problem ? The engine is out of the car now, so i cannot test till friday...

Ok, so the problem was that the motec output voltage excedes 4.99v, and the sensor was doing something funky. Ended up fitting a 100ohm resistor on the 5v wire to the sensor to drop the voltage below 5v, and everithing is working perfectly. By the way, it is a hall sensor