RomRaider

I'm in a debate about the influence of elevation on your tune... His car is tuned on Unichip-Q and he said his car goes rich when he goes to higher places. Something like: from 0.78 lambda to 0.76.

My question is: When tuned direc in to the stock ECU, can't the ECU compensate for the change in atmospheric pressure? Should the WB readings change like that or is it a tune fault?


Thanks for any help!

Ferraz

It might be, that the car is now not hitting the load, that is was tuned w/. Supercharged cars, will definantly see less boost. Turbocharged cars can also, if that turbo was already maxed out, at a lower elevation. So, you are higher in elevation the air density is lower, less air to suck in, less to compress.
I see it a lot here in Colorado. You can go from the plains, at around 3800ft to 11,000+, when crossing mountain passes.
Now, if the car was speed-density or MAP sensor, then the baro input, would be beneficial. But if your MAF-type, your car is only concerned on what that MAF voltage is. If less air is passing thru the MAF, it reads less voltage, which equals a lower load.
Absubtle
CO

As a side-note. I tune all cars, have been for that last 11 years. Honda's run fat up here at 6000FT. Subaru's run really fat, w/ stock tune. As does Mitsubishi Evo's, pretty much 9.0's A/f. I couldn't tell you what they run at sea level, stock, but I am sure it's not that rich.
My absolute atmosphere psi is usually sitting at 12.0psi... where as at sea level, you are at 14.6-14.7psi.
Absubtle
CO

The ECU does have compensations built in that should allow it to handle altitude changes with no trouble. Maybe he's just not reaching high enough loads to reach the parts of the fuel table that call for 0.76 AFRs. What absubtle said, basically. That just depends on how the fuel table is shaped.

However .78 versus .76 is a pretty tiny difference - only about 2.5%. Unless he's got 3-4 pulls at two different altitudes, I think there's a good chance that he's just seeing noise and mistakenly attributing it to altitude.

Consider that the observed difference in lambda might be due in part to temperature also. I can leave my house in Denver and 30 minutes later as I've climbed several thousand feet up I-70 I also watch temps fall often 5-10F. AFR's can change with temperature especially if the MAF compensation IAT table isn't tuned.

Well a properly tuned maf should take care of altitude changes properly, My guess is the fact that he is a running a piggyback designed in the 90's is the issue. Piggybacks aren't the way to tune a car if you want it to run that consistent. Especially over different elevations.

Thanks for the info, guy!

The ECU's compensations for altitude and temperature etc. are never going to be exactly spot on. I have chased my tail tuning back and forth during different temp's and elevations... (because I'm anal and if I'm calling for 11.9 than I expect to see 11.9)...a slight change is nothing to get to worked up over, a lot of change- no, if it's tuned properly