Tuesday, June 25, 2013

Fuel injection modifications- decel pop

I picked up a 2007 Guzzi Griso with 2500 miles on it, Mistral pipe, and a complete shot in the dark for trying something new. I like the look of the Griso and the deal for a 'new' bike was hard to pass up.

The Mistral pipe that was added by the previous owner was without a DB killer. This was typical at the time, but are now included with most Mistral pipes. I was able to obtain a DB killer from MG cycles to help make the bike run slightly better and hide the annoying deceleration popping.

I wished to run the bike without the DB killer and rid the bike of bad fueling down low. Dynojet has come out with a Griso 1100 specific Power Commander V. This allows adjusting the fueling to help the bike run better and cure the popping on 'overrun' or deceleration at zero throttle position.

The base Griso map that comes from the factory:

The area of the map of concern is the popping on deceleration from 4000 RPM to 2000 RPM at zero throttle position (4 degrees on the chart).

The fuel map shows a sloping fuel curve from 1000 to at least 4000 RPM. The corrective action is to remove fuel until the bike stops the pop.

The dynojet map for a stock bike shipped with the unit:
The adjustments made to the dynojet map were to remove 40% fuel from 2000 to 3750 RPM and then taper off from there at zero % throttle. More adjustments were made at 2% throttle to taper off the fuel in the same RPM range, just not as drastic.

Looking at the original fuel map and the modified dynojet map, there might be a little too much fuel between 3000 and 2000 RPM. The end result is correct- most popping has been cured, but some decel pop remains in this configuration. More fuel needs to be removed from 3000 to 2000 RPM in the same ramp as shown in the original map above.

Using the base 2D layout of the stock map, and excel sheet was created to figure out how to fine tune the low end to get rid of all the fueling issues down low. Stock map:
The area in black is the range of fueling I was working with (along with the 4.7 degree next to it). An excel sheet was created with other columns that let me tweek numbers to match a target pulse of the injector:

 These numbers were used in the Dynojet software to help create a more ideal map down low:

The bike ran with the above map for several weeks and another tweak was made to improve transitional popping on throttle movement as well as reducing some harshness in the drive line. The transition from the no-pop map to the stock map that came with the unit needed to be calmed down a bit. The map below was the end result:

End result? No more annoying pop on deceleration and the O2 optomizers improved my idle significantly. The bike is running better than it ever had. Very happy with the results. More feedback on further tuning the the open loop map on a dyno...

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