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Replacing 90s tech with PDM/PMU in FD Rx7

PDM Installation & Configuration

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I have a 94 Rx7 with some questionable body wiring from the previous owner. I would love to maintain all the original street car functions such as wipers, power locks, power windows, sunroof etc but I'm struggling a little bit to find the current and amperage these things require so I can find the correct PDM for this task.

Those of you that have done something similar in a street car, where do you find this information?

I already have a Haltech Nexus that I'm going to use to control all the engine related functions along with the fans and fuel pumps. This PDM project will strictly be for the rest of the car's functions as mentioned above. It would be great if the PD16 from Haltech could fit the bill so I can do everything through NSP, but that's not a deal breaker.

Thanks for any help or suggestions in advance!

Things like fans can have massively different amp draw depending on the particular unit, so I wouldn't count on someone else's data matching yours unless they're using the same fan. That said, if you're buying an aftermarket fan, companies like Spal state the current the fan draws online so it's easily looked up.

The same goes for many fuel pumps. I'd gather info on all the items which the manufacturer does state the current usage for first, then see what you're left with.

For items like the wiper motor, I'd use a multimeter to monitor current draw with the existing wiring to get a ballpark figure.

It looks like the Nexus R5 has 25 amp or 8 amp circuits. An 8 amp MIGHT not be sufficient for the wiper motor, so I'd test that one rather than guessing, and then you'll know what to do.

Fans are aftermarket Mishimoto units and it was pretty easy to track down the amp load for them, 11 amps each. The kit came with a fan relay set up with a thermoswitch. So these don't have to be ECU controlled if there isn't outputs available, it would just be a nice to have.

Fuel pumps, again easy to track down as they're aftermarket units and Walbros, are rated at 14.1 amps each.

The Walbro pumps are pretty high draw, and may need to be on a dedicated power distribution module, which would be fine if as long as it's done well.

It's mainly the OEM electronics that I want to understand so I know if this is feasible or not.


Please understand I'm saying this purely because I want to help get you off on the right foot and your fan selection may alter your circuit choice, wiring, install, etc. I'd use different fans. Mishimoto fans have performed far worse than stock fans in all applications I've tested. I've even seen totally stock cars install Mishimoto radiator and fans thinking it would be an upgrade, only to have overheating issues they did not have with stock components, which were resolved by going back to stock. Especially on an FD, I'd want something proper. They don't fare well when overheated.

On the pumps, did you check amperage at peak pressure you'll be running? Radium has some data at 13.5 V with various pumps and pressure that may help too: http://www.radiumauto.com/Blog/Post/Radium-s-Ultimate-Fuel-Pump-Test-100

Having everything on PDMs vs. some on PDM, some not, really helps give better control and a full picture of total amp draw. If you end up wanting a second PDM, HPA has great material specific to the ECUMasters units which I've been really happy with in the field.

I'll second Mike's comment on the fans. Mishimoto are junk and I've upgraded many cars to Spal's but honestly the factory FD fans are actually pretty good. I wouldn't build your wiring around the assumption of each fan is 11 amps because there's a very good chance you'll want/need to upgrade them. 11 amps is also very vague number, whats the inrush current? whats the FLA? what pressure drop is the fan fighting and what at what CFM? ambient temp and wire size also play a role, so add some head room to be safe. On a Nexus I'd use the 4 big outputs for fans, fuel pumps and maybe starter depending on the car.

Id also 100% recommend putting them on the PDM/VCU. They are critical to proper engine operating and you want good control of them, staging, fuse retries, alarms when tripped etc.

I am actually just finishing an FD Rx7 powered by an AIM PDM32, so I'll be able to answer many of your other questions in a week or two. I always bench test items I am uncertain about amp ratings for.

I'll also second Mike's recommendation of the ECUmaster PMU, its the best PDM of all the ones I've used so far!

Mike and Tessson, thanks for the replies!

I will ditch the mishimotos and go back to the stock fans, not a problem at all.

Also, I started the club level wiring course and, to my surprise, the example worked throughout the course is a FD Rx7! I'll make my way through that before I come back and ask for anything else from y'all.

Thanks for the support so far!

Excellent. Tyson, best of luck on your project as well.

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