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Plug Whisperer
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Especially with your access to the ECU, would it be possible to use a wideband O2 sensor with analog out to force the ECU into closed-loop at WOT and target a richer setpoint? Wideband gauges can have a programmable output, so it seems like one of those "how hard can it be" kinda things.
 

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Nein Kinder
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@turbophil - Great article!

After reading this and some past comments, I’m concerned my OEM setup is running perpetually lean. I have a 2011 Elise SC and most of my operations are at 6,000’ - 10,000’ MSL with occasional excursions to 4,000’ and 12,000’ MSL. It’s not very precise, but cruising at 4,000 RPM, I get 30 MPG at 9,000’ and 35 MPG at 12,000’. That seems pretty lean to me.

I know the MP42 with no intercooler is a dead end for more power, but is the AFR something BOE could address on my vehicle?

Glen
 

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Sold my Exige S
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^ That's normal and is not necessarily lean. Air density decreases aloft, so the fuel injectors are scaled back to maintain ideal AFRs (this is not lean since there's less air being compressed). You'll see similar MPG results driving in extreme cold versus extreme heat at the same elevation.

The only problem is you're making less power from reduced compression at higher altitudes. Just be glad you have forced induction to help out!
 

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For general tune and running verification, you’re interested in a single operating condition, which is steady state WOT. You’re not interested in AFR at idle, as the ECU is forcing the idle to be at stoich through its closed loop operation using the primary NB02. It is common for a WB02 to not have great idle AFR data and will often show a lean indication at idle. This is due to a variety of reasons. Do not be alarmed if you observe a lean idle on your WB02 as it likely erroneous. You can verify your idle AFR with a scan tool and monitor the factory NB02 and the corresponding fuel trims. The idle AFRs are not a common problem and generally not a tuning issue due to the closed loop operation.
At idle, my AEM Wideband creeps up and off the charts pretty quickly and goes to --, also the exhaust gets really loud (like I have a 67 Hemi GTO or a small top fuel dragster) and when I touch the gas the AFR pulls right in to normal ranges (goes green) and it sounds smooth as butter. Does this sound normal?
 

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At idle, my AEM Wideband creeps up and off the charts pretty quickly and goes to --, also the exhaust gets really loud (like I have a 67 Hemi GTO or a small top fuel dragster) and when I touch the gas the AFR pulls right in to normal ranges (goes green) and it sounds smooth as butter. Does this sound normal?
It sounds like your sensor is too close to the exhaust tip which allows outside air to corrupt the signal when the exhaust pulses are spaced out. Sometimes you have to just run open loop at idle for this reason, especially if you have no cat between the sensor and outside air. This is why I always cringe when I see shops put a sensor in the exhaust tip to do dyno tuning. Odds are that reading is garbage at low-ish rpm. Or you could just have a calibration issue.
 

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Running PPE headers (SC) with their decat. Sensors are in their bung holes. I may try it with the sport cat instead of the decat and see if it changes anything.
 

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Nein Kinder
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^ That's normal and is not necessarily lean.
I’m a pilot and quite familiar with leaning out the mixture as altitude increases. But Phil’s document indicates the (OEM?) system tends to produce leaner than desired mixtures as altitude increases. It’s probably not a problem for most drivers, but I’m routinely two miles above sea level and occasionally as high as 14,250’ MSL (bonus points for figuring out where - I’m 20 miles away).

Glen
 

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Plug Whisperer
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Discussion Starter #9
I’m a pilot and quite familiar with leaning out the mixture as altitude increases. But Phil’s document indicates the (OEM?) system tends to produce leaner than desired mixtures as altitude increases. It’s probably not a problem for most drivers, but I’m routinely two miles above sea level and occasionally as high as 14,250’ MSL (bonus points for figuring out where - I’m 20 miles away).

Glen
Hi Glen,

I didn't mean for it to read that the AFRs are leaner than desired... It's more that the SC'd cars start exhibiting NA like AFRs and that's because they essentially become NA manifold pressures at altitude... and then at the heights you're talking about, they won't even have the same air density as an NA car at sea level.

So the ECU is doing the right thing by allow for a less rich condition as manifold pressure drops.

That said, the Lotus SC tune at sea level is a horrid bit of code and blows up the SC regularly on track, IME. At 4,000+ feet, I don't think you'll see a SC'd car pop however. Any SC (the M45 from Lotus with their tune) that sees track time should run 100 octane and do a dance for their preferred deity...

Hope that helps,

Phil
 

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Plug Whisperer
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Discussion Starter #10
^ That's normal and is not necessarily lean. Air density decreases aloft, so the fuel injectors are scaled back to maintain ideal AFRs (this is not lean since there's less air being compressed). You'll see similar MPG results driving in extreme cold versus extreme heat at the same elevation.

The only problem is you're making less power from reduced compression at higher altitudes. Just be glad you have forced induction to help out!
That's right... At altitude, the first few PSI of boost just deal with the parasitic drag of the blower... Once you're to 6,000 feet or so, with most of these blower cars, they run like an NA car at sea level.

At idle, my AEM Wideband creeps up and off the charts pretty quickly and goes to --, also the exhaust gets really loud (like I have a 67 Hemi GTO or a small top fuel dragster) and when I touch the gas the AFR pulls right in to normal ranges (goes green) and it sounds smooth as butter. Does this sound normal?
May have an air leak... The PPEs and 2bulars have thin flanges and often leak at the head. Each exhaust pulse carries a vacuum behind it and will draw in fresh air if it can. At low throttle opening, it doesn't take much air to throw off the readings... At idle, not a big concern... At higher RPM, there's enough exhaust gas available that small air leaks are essentially unmetered.

Especially with your access to the ECU, would it be possible to use a wideband O2 sensor with analog out to force the ECU into closed-loop at WOT and target a richer setpoint? Wideband gauges can have a programmable output, so it seems like one of those "how hard can it be" kinda things.
That would be a fantastic amount of work... to that end, a good MAF based closed loop system is hard to beat. No finicky 02 sensors to fight you! :)

-Phil
 

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'I have a 05 Elise with a BOE REV300 and operate a 4700' in elevation. If I install a smaller blower pulley to get my boost up to the same psi as a sea level car will my AFR read the same as a sea level car? Currently it runs just under 13:1 under boost all the way up to redline, witch scares me.
 
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