do afr's lean out when living 3300' feet above sea level??
please someone explain i only found on one thread were wartalon had to get himself retune cause he moved to 6600' feet above sea level he said that his afrs leaned out on him anybody elso experienced this??
thanks

 

Mine did, but I don't know why. I went from a mid-11 AFR tune to a 12.0-12.2 AFR tune just by moving. The absolute numbers aren't important. What's important is that both AFR figures were taken by a sniffer in the tailpipe and done on the same type of dyno (Dynojet). So, even if they were reading higher than actual, there was at least a half point change (leaner) when I went up 5000+ feet.

 

If this was the same WBO2 installed in the car I would be more inclined to give the numbers some credibility, but with the variation I see from one dyno's WB to another, I'm not so sure I trust them. If one dyno operator puts more race gas through his sensor than another, it will start to read leaner. And it will start to drift before the obvious signs of degradation appear. Locally there are some dynos that really try to discourage you from using race gas on thier WBO2s, others that charge 25/hour extra, and some that simply don't care. Many of them use the more expensive sensors, while some use the cheaper VW sesors and are probably more likely to replace them often. With so many variables I have to question the results. You may know more than you are posting though, so I'm not trying to be argumentative, just posing the question.

The ECU should be able to detect the change in altitude through whatever air metering or pressure based system it uses, and adjust fueling accordingly to mainain the target AFR. But of course, that doesn't automatcailly mean that it does a good job of it. I've never changed altitudes more than 1000 feet or so, and never took readings on my WBO2 at the higher elevations, so I can't provide any meaningful feedback.

 

thanks warr!
also when seeing less boost you lean out correct me if aim wrong??
do you think that because we are at a higher alltitude we have less absolute pressure in the intake manifold and this gives a leaner afr??

 

I really don't know - it makes my head spin trying to figure it out. I was definitely seeing less absolute pressure up here without changing anything, so maybe my tune for higher boost made me lean, but the ECU really is supposed to compensate.

 

Not to hijack, but you're saying a tune done at sea level will lean out at high elevation? I always thought it would run rich because the ecu would detune itself to compensate for the thin air.

 

Reno, that is what I expected when I moved, because I thought the thinner air would mean less "air" and thus more fuel in the AFR ratio, but the massive change in elevation meant a much lower atmospheric pressure and thus much less actual boost. I was surprised when I got on the dyno and was rocking a 12.0-12.2 AFR. Al showed up 2 weeks later to retune me, and his first 3rd gear pull showed the same 12+ AFRs on the road, so we fixed that right quick.

 

it makes me wonder also but i hope someone else helps us!

 

You guys really have me worried now because I'm getting tuned in the near future (at sea level) and then driving back home to about 5,000ft. elevation. I spoke with several reputable tuners and they insisted that the only negative effects I would see would be a slight decrease in peak power and spool up. I specifically asked if the major change in elevation would cause me to run lean and make me more prone to knock, and they told me absolutely not. They said the ECU will compensate for the thin air and detune itself accordingly thus being "slightly safer than the original tune at sea level." So were they just bs'in me or did they just give me a theortical answer that should be the case???

 

wow i hope i could help you but i also need to know this??

 

bump for a straight answer. This issue really has me concerned now about getting tuned at a much lower altitude.

 

ECUs are mapped so that you run richer as your engine load increases. At high altitude, you're max engine load is lower than it is at sea level. Especially when you reach the limit of your turbo flow capacity (as just about all of us do with basic bolt ons). You'd probably run the same AFR up there as we do at sea level with 3psi less boost. Which is approx 1 point leaner.

-shiv

 

also i keep seeing that my afrs lean out by 7000rpms to 8000rpms is this normal is it cause we have less boost at higher rpms??

 

thanks shiv
so whats with the 7000-8000rpm lean out do you think its my fuel pump on its last minute?? or is it cause of the boost i see like 17psi of boost in redline!

 

You have to love tuners that actually understand the details....Nice job Shiv.