Tuning the Guzzi EFI

May 22, 2012
by mike

The following is Mike Haven’s article from the MGNOC Newsletter on Injection Set-Up for all Guzzis

This system is an open loop type.  It uses air and cylinder head temperature sensors. These are NTC, negative temperature coefficient.  As they heat up the resistance goes down. The electronic control unit (ECU) is the brains of the outfit. It sends a low current voltage signal to these temp sensors where it is “grounded” to a varying amount based on the temp. The throttle position sensor works in a similar way. More throttle angle, more voltage.  The signal from ECU to these sensors is known as reference voltage. About 5 volts open circuit.  The camshaft position sensor is an inductive type. It counts the teeth so the ECU knows where the pistons are in their stroke and the engine speed. So the ECU knows speed, load and temperature of air and engine.  The big three.  But not exactly how much air. So all this info goes into the ECU. It decides in an instant how much fuel to inject on the next cycle. Both injectors get the same signal. The amount of fuel is governed by the time the injector is turned on or open. This is the “pulsewidth”. .It’s measured in milliseconds. Around 3 ms is normal idle pulsewidth.  It is much more under heavy acceleration.

In theory this is all great. These systems have had problems on bikes ,and not just Guzzi’s. Mainly because of cost or space limitations, there have been no provisions for measuring the actual induced air. It’s a calculated model at some elevation .A real air mass meter with oxygen sensor closed loop control would make for a bike that runs perfect.Not likely to happen. So lets make the most of what we have to work with.

Any maladjustments can turn a great running bike into a sputtering pig. These are much more sensitive than carbed bikes. To start the setup you will need a very accurate way to balance the throttle butterflies. I have used mercury sticks, but really have been impressed with the convenience and precision of the Twin Max electronic balancer. Access to an exhaust gas analyzer is a boon.

There are brass bypass screws on the TB’s. Turn them in counting the turns until closed. Write it down. Connect your balance meter/carb sticks and start bike. Ignore the fact that it runs worse than it did. The TB must be adjusted to a very fine degree of balance .Most models its done with a plastic thumbwheel under the left side TB. The most important part of the synch is to do it at 3000 rpm .This is where the engine moving some air. Hold throttle steady. Don’t worry about what it does at idle right now. After the synch is as good as you can get it, you can see if the base position of the throttle plates is close at idle. Disconnect the linkage from left to right for this step on 4 valves .There are stop screws under the TB if this needs adjustment. Then check the balance at just off idle. Set the bypass screws to the specs first. If out of balance adjust the brass air bypass screws. There are new specs for the air screws and TPS. See chart.

The point here is to insure that both cylinders are getting the exact same amount of air. Because they are going to get the same amount of fuel ,whether its right or wrong. Since there is no provision in the system to measure the actual induced air the system is dependent on this basic fact. At the CO specs MGNA and EPA agree on it is not really set too lean to run right. If there is not air induced that is not part of the original equation. After all this balancing act is done you should have a fairly decent running bike. The next step is to check the idle CO. (Carbon Monoxide)This step requires the gas analyzer. It is adjusted by a screw on or in the control unit up until the 15m system. 99/up.These require a PC and the Marelli software to do the screw turning electronically. Richening up the bike get rid of flat spots or running faults is rarely the answer. The screw or PC only has effect at idle and just above. See specs chart for your model.

The above applies to all but the Quota ES. Poor old Quota, it got a bad rap because of the fact that most of them run bad as delivered. This is again due to an air imbalance. Not a lean condition. Fixing it is a little more work but it can transform a bike from insufferable to quite nice in a short time. The unique( to MG ) single throttle is actually another automotive part. It looks like the base plate of a Weber 2 barrel carb. The butterflies are geared to each other by a pair of arc gears. One of these has a screw that holds it in relation to the shaft that it turns. This is the one for the left side. The TPS is on the shaft for the right side. See where the problem lies? The Weber factory claims that these are set on a flow bench and are perfect. NOT. The earlier method of providing a “balance “ was with the bypass screw on the right side of the TB. It should be closed lightly and never be opened again. Ever. Now the fun starts. Gain access to the screw on the front of the left side gear. A 7 mm socket on a flexible handle will get to it. Then connect balance meter and run bike at 3000 rpm. The more precision you can muster ,the better your bike will run. Perfection is acceptable. After this the idle should be in balance on its own. If not , tough. Leave the bypass screw alone closed. Set TPS and CO. A note on TPS. There are many methods floating around. The specs provided are intended to be used on a bike that has all throttle linkage in place,at idle. Live running measurement.