PDM output spikes

[Fast_Moto]

I am running a motorcycle with a PDM, M1 ECU, and RBW throttles. Whenever I slam the throttle shut, I get huge spikes in the rear wheel speed. The speed sensor and ECU power is supplied by the PDM.

I did a bunch of testing and here is what I found:

1. There is no issue if the speed sensor is connected to 12V directly from battery. It does not matter whether the ground or signal wire is routed through the harness or through a lengthy external wire.
2. If the speed sensor is connected to the PDM, the spikes show up regardless of whether the power is supplied through a wire in the harness or through a lengthy external wire.
3. None of the other sensors show similar symptoms. The front wheel sensor takes a 6V input and does not show this symptom. When I connect the rear speed sensor to the input for the front wheel, I get the same issue.
4. This happens primarily when the twistgrip is released instantaneously (from part or full opening) and the throttle slams shut. If I open the twistgrip unrealistically quick, I can sometimes replicate that issue, but it is rare. Slow, deliberate throttle opening does not cause any discernable disturbance.
5. The speed spikes I get are as little as 7km/h to almost 100km/h. Sometimes I can see an up/down trigger in the traces as a result of throttle opening, other times I do not yet still see a speed spike. I turned up the filtering, etc. (e.g., filters all pulses smaller than 136 us.) to no avail.
6. If the spike shows up in the voltage reading for the sensor, it mimicks a a triggered voltage signal. In other words, it only changes between the two voltage states (high and low). There is no random voltage read.
7. We have been having issues with rear wheel speed noise on two separate motorcycles (different brands) with the M1 ECU during operation. I will post a separate thread about this at a later time, but I wanted to get some feedback on the PDM issue separately.

Any ideas what may cause this problem?

[Merlin]

I would look at your RBW ....might be going over max current draw for the system and creating a spike ?

John P

[Holmz]

I would look at your RBW ....might be going over max current draw for the system and creating a spike ?

John P

Or using a lot of current for the throattle and either generating and inductive load back emf when the throttle shuts to do some thing (???). Or a lot of current and a magnetic field to couple into the other sensor.p

[Scott@FP]

Chain slack and reversing torque direction?