PDM Grounding

hey all, just want to clarify the best point to ground my PDM (Link Razor).

I'm installing it on my NA MX5 which I previously installed a Link Monsoon and used a start point ground to the back of the head. Happy days.

I've gone through the PDM and wiring courses and it probably just hasn't sunk in entirely :D I just want to be sure. I would say to the engine also to avoid voltage difference but, happy to be told otherwise since that would be the most difficult. I'm not planning on using any H-bridge, simple ITB setup.

Thanks!

Hey Daniel,

If you've already taken the time to star-point ground your ECU, personally I'd probably do the same for the PDM as well, provided it isn't unreasonably difficult. It keeps things nice and consistent.

That said, you wont have any issues grounding the PDM to a good chassis point either, as long as the chassis has a solid connection back to battery negative.

Even if the PDM is supplying power to the injectors and ignition coils, those loads aren't actually using the PDM ground as their return path. The PDM is only supplying the positive side, while the injector current returns through the ECU drivers and the ignition coils return through their grounds on the cylinder head. So provided the engine, chassis, and battery grounds are all well bonded together, a chassis-grounded PDM will work perfectly well.

The Razor also has dedicated sensor ground pins for its analogue inputs, so the main power ground location won't affect the sensor reference back to the PDM. Any communication with the ECU is over CAN as well, so small ground offsets between the devices won't affect the data being transmitted.

Personally, on an OEM-based build where the majority of the factory wiring is already chassis grounded, I'd probably chassis ground the PDM as well. If it were a clean sheet motorsport build where everything was already star point grounded to the engine, then I'd ground the PDM there too.

Grounding can get a bit confusing, but the main things I'd focus on are having a good low-resistance ground, only grounding each device at a single location (don't ground it to both the engine and chassis), and keeping the sensor grounds dedicated to sensors only.

hey Caleb, thanks for that detailed reply! That's super useful :)

The MX does ground straight from the battery to the chassis from factory so that is super convenient anyway and I know reliable.

Thanks again!