Fuelling at altitude....
 

Just come nack from annual blast along Pyrenees and it became apparent that my Bos Rep was not fuelling well at altitude. Went very woolly over about 1700m and a lot of farting and backfiring on the overun coming down. Cleared at lower altitude. I do these sort of trips twice a year so am loathed to go to the expense of a power commander 3 and set up etc, but what's anybody's experience of how they affect the fuelling/feel of the engine, and what will it cost?

I know there's a guy selling them by the dozen on eBay, but are they worth it and what should I pay?

Interesting, i go down to Andorra a lot (st4s and on a 996sps) they both lose power at high altitude but i've never experienced your problems. Similar sort of altitudes.

When you ride in the mountains, the air is thinner so the engine will run too rich without a correction to the computer’s fuel map.

Ducati’s engine management system takes input from an atmospheric pressure sensor that monitors the atmospheric pressure so that the computer will supply additional fuel at lower elevations and up to 8% less fuel at altitude.

Unfortunately, 8% is often not enough so the bikes still run rich at altitude. Earlier model (851) base fuel map corrections went as high as 32%. Unfortunately, they really ran crappy when the sensor failed so Ducati changed the programming to max out at 8%.

The sensor's output varies for pressures between 17 mm Hg (0.25 volts) and 787 mm Hg (4.75 volts.) So an open circuit (0 volts, a common connector failure) makes the computer think that the engine is operating at a very high altitude so it reduces fuel by the maximum amount to compensate.

It used to be that you’d get around a 13% correction at 1700m but now you only get around 5% with the stock chips.

So, the solution to your problem is to get an EPROM that uses a larger (32% max) fuel map correction for altitude.

The UltiMap chips can be supplied with the altitude correction recalibrated.

http://www.fuelinmoto.com.au/

They state: “Simply add a 'P' to the order code (for example UM081P). These need to be ordered specially, as they will make your bike run poorly if the altitude sensor develops a fault.”

Thanks Shazaam, a typically thorough reply. I think that one of the regular posters on here runs/works at pro v twins who import the Ultimap system, can anyone tell me who it is?

One thing from reading the guff on the site...it says that the immobiliser function is switched off ( I guess amongst other things)...what does this mean?

By the way, the problems weren't horrendous, but a snatchy pick up on some of those fabulous twisties high up and the popping on the overun on the way down does slightly spoil the fun!