VEMS looks to be just the thing I was looking for to go beyond carburettors.

My project

I will use the bike for street use only. Basically, I want to learn hands-on about EFI. I am not looking for a performance increase. Lower fuel consumption might be nice, though.

Me and my Guzzi on a cold morning last winter:


Bought lots of second hand EFI bits from a Moto Guzzi Quota to make a start.. :)





At present I only have this (VRS) trigger for the ignition on the camshaft. There is no cranksensor.


I want to make a new rotor for this with more pulses. At present I am thinking of 12-1 teeth. Since I have two pickup coils (135 degrees apart), I can then do 'static' position detection: Normal operation means the two pickups generate alternate pulses and the missing tooth gives two consecutive pulses from the same sensor.

Good point. However, the pickup has two trigger coils that are 135 degrees apart, so I can do a correct trigger-tooth selection with *any* number of teeth, pickup #1 will do the left cylinder, and pickup #2 will do the right cylinder. This requires VEMS with two VRS inputs, but VEMS hardware supports this. On a related note, I have since found a factory trigger wheel that fits the crankshaft. That would mean no home-made trigger wheel for the camshaft would be necessary. The factory crankshaft trigger wheel is 4+1 teeth (three single and one double tooth). Does VEMS firmware support such a configuration already or will I need to modify the firmware myself?

MAP sensor I have is rated at 100 kpa. 100 kPa should work well in an NA engine. No need for the 250 kpa sensor (but that would work too).

Fuelpump PWM

I am rather short on electrical power. I have a generator that puts out 280W at most, and after 80W for lights and 25W for heated handgrips, that doesn't leave a lot for EFI. I was thinking of doing PWM for the pump to save power. I can see two possibilities.

a) Measure fuel pressure, no return line, and PWM the pump to keep the pressure constant.

b) Keep the pressure regulator and the return line, but PWM the pump (feed-forward, based on injection pulsewidth, RPM and battery voltage, all of which the ECU knows), to keep the return-flow as low as possible to save power.

PWM-ing the fuelpump seems more risk than benefit. Also, you want to have available electric power even at maximum engine power.

175W / 12V = 14.6A

Yes, 11A is enough for the fuel pump. (I measured it at approx 4 A). But full-power is not where the problem is. The problem is extended running at low RPM (city traffic), where generator output is (far) less than the rated 280W. I would also like some current left to charge the battery. Fuel pump PWM would be useful there. I agree that this is probably not something to start with; (enough variables as is), but it is certainly possible and useful, so I want to keep this option open for the future. I see no real reason not to. A spare injector FET should drive the fuel pump without a relay with no problem.

Apparently, there are some Ford Focus engines running with a PWM'ed fuel pump (and no fuel return line?). If Ford can do it, so can I... :)

PWM'ing the fuel pump is a very useful feature on many cars, for example the extremely powerful Weldon race pumps that emit a high pitched roar that drown out the engine at idle and makes it hard to hear what people are saying if you stand too close too the car. These quiet down to only be a bit louder then an ordinary high power fuel pump when they are driven at a lower voltage. The Weldon pumps will of course need external switching hardware as they consume quite a bit of current. -Jörgen

PWM'ing is also useful with pumps like the Bosch 044 as it allow a stock type fuel pressure regulator to regulate the pressure even at low loads. It's common to see that the fuel pressure increase a bit at idle because the regulator can't deal with the flow. We try to keep the stock type regulators as long as possible as most aftermarket regulators have serious problems. -Jörgen

But trying to regulate the pressure of the fuelpump is technology for technologys sake which is always bad. An open loop table where the the PWM percentage is mapped over load and rpm is what the above car applications need. You basically let the pump run at half speed when idling and when driving at low load/rpm but over a certain threshold in the table you disable the PWM and let it go at full speed. Extras: Controlling a relay that bypass the fuelpump PWM when it's at 100% to avoid having all that current flow through the FETs. We also need a settable fallback lag that allow the pump to continue at full power during shifts and when feathering the throttle. - Jörgen

The fuelpump manufacturers own applications for slowing down the pump at low load use a proper regulated and smoothed switched powersupply. I can only draw the conclusion that the pumps don't like to be PWM'ed from this fact. So at the very least we need a small box with an inductor and a big capacitor for the directly switched applications. For the larger pumps we need external switch hardware as well, but that is easy to implement if the pulsetrain itself is available from the ECU. This could be built with boost capability itself which would make it viable as a standalone product. -Jörgen

Thanks for your input!