Re: VDSTS Info - Instructions
john zibell said:
Adjusting fuel trim on the 5AM is open to debate. Since the lambda sensor provides feedback to the ECU to adjust injector pulse, some think adjusting trim has no impact on fuel delivery. Other think it may have some impact at RPMs above the closed loop operation range. That said, I have noticed fuel efficiency improvements by setting the trim more negative but the matter is open to debate.
John,
Hope I’m not opening a can of worms by stating my opinion ……
I was reading up on the MM type ECUs and it’s function to figure out what parameters would be useful when hooking up to the VDST……The Guzzi is type MAP which is to say that the volume of air is deducted by the angle of the butterfly (angle alpha)
TPS and
engine RPM (number of turns n). The mass of this corresponding volume of air is corrected by the
air temperature and the
atmospheric pressure.
This allows you to calculate the
injection times according to stocked mappings in the ECU. Therefore on this injection type, the air volume is not measured (no flow meter)
Calculated in the stock mapping of the ECU ….at low rpm (idle) the mixture is stabilized towards poor (lean). On acceleration or full load and beyond 4000tr/min or out of range to its norm the mixture is rich.
Looking at the Lambda probe you should see it vary from lean to rich according to a cycle of 1 second. Besides if you have the fine ear and that you can stabilize the RPM to ~2000tr/min you will be able to see this variation on the VDST. (Note: the probe has to be at a hot operating temperature…..to give a good value) The sensors only work effectively when heated.
Voltage specification of a typical
lambda sensor voltage on an automobile ECU.
An output voltage of 0.2 V (200 mV) represents a "lean mixture" of fuel and oxygen.
An output voltage of 0.8 V (800 mV) represents a "rich mixture", one which is high in unburned fuel and low in remaining oxygen.
Air-fuel ratio for gasoline is 14.7 to1 of mass volume ……. In return you should be able to detect an average value of 0.45 V (450mV) on the sensor.
All this said if you adjust the fuel trim you should be able to see a variation on the lambda probe voltage compared to the previous fuel trim value at 2000 rpm.
Given that
engine temperature, air temperature, atmospheric pressure, TPS are all same valves as before.
So to see if all this theory works I tested it out with the VDST software.
I used all the parameters that are in bold…..
Got the engine to warm up ….. used a fan to keep it cool while doing the tests…..
Checked the lambda probe voltage.
At 2000 rpm give or take a few 100 and the fuel trim at 80 lambda probe voltage averaged 12mV.(Felt engine running smooth)
Fuel trim at -80 lambda probe voltage averaged 161mV.(Seemed to be running rough) and at 2000 rpm give or take a few 100 and the fuel trim at 0 lambda probe voltage averaged 50mV.
I guess adjusting the fuel trim does have an impact on the fuel delivery.