Resurrection of PWM Motor Controller


Have been doing a little bit of research and thinking, dangerous I know.

One of the reason I want to create a PWM motor controller is to limit the noise that these motor make when driven by very low PWM frequencies that the MS3 PWM O/P’s provide as well as utilising it in a returnless fuel setup.

One of the problems is that the MS3 and or TunerStudio MS has a limited set of output frequencies (11.1Hz to 250Hz) to drive motors in closed loop PWM control. From my research frequencies required to make the motors run quietly (hopefully in the upper audio frequencies) and still maintain sufficient torque and not overheat, vary wildly depending on the motors electrical and mechanical characteristics.

A test I did a year ago using MS3 resulted in a awful lot of noise from the motors using the MS3. Like my fuel pump was a coffee grinder and the radiator fan was not much better either!


The implementation would look at the duty cycle of the input (from MS3) and switching the output to the motor at the same duty cycle but at a user selectable frequency (possibly at a multiple of input frequency). I won’t go into to many details as I’m still thinking of the design plus I’ll be doing some prototyping shortly, but it will:

  • be a micro controller based design
  • have high speed opto-coupling of the I/P (very important if there is a problem with the O/P you don’t want high voltage fed back into the MS3)
  • have user selectable PWM switching frequencies either as multiples of I/P frequency or it’s own configurable frequencies
  • it will work out the dwell (duty cycle) of the I/P from the MS3
  • it will either have medium current IGBT or MOSFET O/P transistors.
  • be contained in its own splash proof case
  • mounted close to the motor to minimise the EMI from the high frequency current wires

At this stage I’m just investigating and prototyping…

To MAF or not to MAF?

I’ve decided to expedite the installation of the MAF (Mass Air Flow Sensor), by installing it now in phase III, not phase IV as originally planned.

Part of the reason is cutting down on effort tuning one system, as the SD system is tuned differently. There appears to be more people using MAF nowadays, so maybe I’d be doing less pioneering, and will be able to leverage off others expertise. Plus I think I’d be the only person with a ’68 Morris Mini that was running a MAF system??

BOSCH MAF 0280217123
BOSCH MAF 0280217123

I’ll be using a K&N cylindrical air filter. Some people have said not to use the oiled mesh type of filters as the oil contaminates the MAF sensor, but after looking at text and video footage on the K&N web site, which they disprove this myth, I’ve decided to go ahead and use the filter. I have very little room under the bonnet (hood) so it would be a tight squeeze for this filter let alone if I had to make a cold air filter box and use a dry paper element.

K&N CM-8012 Air Filter
K&N CM-8012 Air Filter

Hopefully the compromises in layout of the air filter trunking etc will not adversely affect the performance of the MAF. Time will tell!

EFI Rebirth – Or Never Say Never Again!

Why again?

As the title says, never say never again … I have changed my mind once again. The main thing I noticed in previous EFI installations, was that the increased torque down low, a result of better mapping of the ignition. Also a smoother idle when hot and also cold.

I need a project, and I was thinking of making my own programable ignition, but being basically lazy, well you get it don’t you?

I intend to document my steps along the way, and hopefully someone might get inspired by my ramblings. I’ll call this phase, Phase III.

Walbro 5CA401 Fuel Pump

One of the disappointments from the last attempt, was the Walbro 5CA401 fuel pump SPI replacement that I fitted. It is louder and has more of a rasping tone than the original Rover SPI fuel pump, P/No 6443434 which is more of a whir. The Rover one I think is using a different type of pumping mechanism.

If you look at the picture, you will see that the Walbro is half the size of the Rover pump. It stands to reason (maybe?) that the Walbro has to work harder, hence more noise. Does anyone else with this pump, notice the louder noise?

I’ll keep the Walbro in situ, and see if I can live with the noise, maybe I can put some Dynamat sound deadening on the outside of the petrol tank to dampen the noise.

The Walbro 5CA401 is rated at a minimum of 109 litres/hour or 29 US Gallons/hour @ 12PSI

Walbro 5CA401 on left Rover 6443434 on right
Walbro 5CA401 on left Rover 6443434 on right
Walbro 5CA401 Fuel Pump in pickup
Walbro 5CA401 Fuel Pump in pickup

RIP Eddie

Now for a sad note. My faithful companion of 11 years, Eddie the dog was put down in January 2016 as his heart finally failed him.

Eddie was a constant companion out in the workshop and around home, and I will miss him greatly.