951 Altitude Issues
10-07-2002, 06:39 AM
#1
Three Wheelin'
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951 Altitude Issues
I had my car up in the mountains around Lake Tahoe this weekend. I went up to as high as 8,000 ft. Anywhere above about 4,000 feet, if I ran at full boost (1 bar) for a couple of seconds, the car would disable the cycling valve and the highest boost I could realize was (.4 bar). Restarting the car brought it back to normal operation (not the best thing to do on a dark road at 75 mph, but I'm still alive). If I didn't quite go WOT, I could get a higher boost and performance level without triggering the limp mode.
I suspect that my altitude compensation box is either not functional or disconnected. I am going to investigate it when I get a chance. I researched the operation of it and was very surprised to find that it is simply an off or on circuit triggered around 1000 meters. I imagine that the ecu is either seeing too rich of a mixture at the O2 sensor or knock is being detected due to the turbo working extra hard at altitude, heating the air higher than usual.
I suspect its just the O2 sensor reading WAY rich. Further, low rpm operation was extremely sluggish and the car took a little longer to start.
I wish I had brough a led and a list of the klr error codes so I could see why it was going into limp mode.
Anyone have some insight to add to this. I did a search on the list and noticed that someone else who lived at high altitude was only able to see .4 bar. They claimed that a Huntley wastegate fixed it, which is not surprising since their setup likely took the klr completely out of the equation.
BTW, pertinent info on engine mods:
K26/8, LBE, chips, 15psi
I suspect that my altitude compensation box is either not functional or disconnected. I am going to investigate it when I get a chance. I researched the operation of it and was very surprised to find that it is simply an off or on circuit triggered around 1000 meters. I imagine that the ecu is either seeing too rich of a mixture at the O2 sensor or knock is being detected due to the turbo working extra hard at altitude, heating the air higher than usual.
I suspect its just the O2 sensor reading WAY rich. Further, low rpm operation was extremely sluggish and the car took a little longer to start.
I wish I had brough a led and a list of the klr error codes so I could see why it was going into limp mode.
Anyone have some insight to add to this. I did a search on the list and noticed that someone else who lived at high altitude was only able to see .4 bar. They claimed that a Huntley wastegate fixed it, which is not surprising since their setup likely took the klr completely out of the equation.
BTW, pertinent info on engine mods:
K26/8, LBE, chips, 15psi
10-07-2002, 09:53 AM
#2
Race Director
Hmmm, this is odd.... Sounds like you're getting overboost protection even with aftermarket chips? Also how can your CV lower your boost if you have an LBE installed? Wouldn't that take precedence over the CV, even if the're both in series with each other? Strange....
To test if the altitude sensor is causing this issue, disconnect it from DME line #30. The DME leans out the mixture 6.3% when the altitude compensation is triggered. That might be a bit too much for the altitude where you were, maybe causing a lean mixture? Or the chips you have may have a different value for altitude compensation.
Don't know where you would go to test this anyway... Mt. Hamilton?
To test if the altitude sensor is causing this issue, disconnect it from DME line #30. The DME leans out the mixture 6.3% when the altitude compensation is triggered. That might be a bit too much for the altitude where you were, maybe causing a lean mixture? Or the chips you have may have a different value for altitude compensation.
Don't know where you would go to test this anyway... Mt. Hamilton?
10-07-2002, 11:45 AM
#3
Nordschleife Master
8,000ft ???
It's not that you shouldn't be driving a car that high up, but honestly, I don't think Porsche ever designed the car with that kind of altitude in mind.
Secondly, If the altitude correction box and DME were any good, they would gradually lean out the mixture as you got higher - as opposed to applying one correction value over a fixed altitude.
Whether the problem is porsche component specific or not - I dunno, but if you are driving that high up regularly, I would suggest looking into newer aftermarket components that correct gradually, with altitude.
It's not that you shouldn't be driving a car that high up, but honestly, I don't think Porsche ever designed the car with that kind of altitude in mind.
Secondly, If the altitude correction box and DME were any good, they would gradually lean out the mixture as you got higher - as opposed to applying one correction value over a fixed altitude.
Whether the problem is porsche component specific or not - I dunno, but if you are driving that high up regularly, I would suggest looking into newer aftermarket components that correct gradually, with altitude.
10-07-2002, 12:20 PM
#4
Three Wheelin'
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[quote]Originally posted by Danno:
<strong>Hmmm, this is odd.... Sounds like you're getting overboost protection even with aftermarket chips? Also how can your CV lower your boost if you have an LBE installed? Wouldn't that take precedence over the CV, even if the're both in series with each other? Strange....</strong><hr></blockquote>
I thought that the klr could go into limp mode for several faults beyond just overboost protection.
Doesn't the lbe just provide the initial delay of air pressure, and then just opens and acts as a slight restriction. I assume that this restriction is what is causing it to boost to .4 bar instead of .2 bar.
[quote]<strong>To test if the altitude sensor is causing this issue, disconnect it from DME line #30. The DME leans out the mixture 6.3% when the altitude compensation is triggered. That might be a bit too much for the altitude where you were, maybe causing a lean mixture? Or the chips you have may have a different value for altitude compensation.
Don't know where you would go to test this anyway... Mt. Hamilton?</strong><hr></blockquote>
Thanks for the information. Beyond the DME leaning the mixture out 6.3%, does it do anything to timing or tell the klr to adjust the boost level? Does the klr increase its knock sensitivity? On another note, does the klr, using its' internal map sensor, tell the dme to vary the mixture even when off boost?
Thinking about it further, at WOT, the O2 sensor doesn't do anything. Further the air temp sensor sits in front of the turbo near the airbox along with the afm, and the coolant temp sensor wouldn't have any effect. The only thing that would tell the computer to go into limp mode would have to be the knock sensor. So, even though the mixture may be a bit rich, the main problem is likely the turbo is way past its efficiency range trying to go from .75 bar absolute to 2.0 bar absolute and it is superheating the air.
<strong>Hmmm, this is odd.... Sounds like you're getting overboost protection even with aftermarket chips? Also how can your CV lower your boost if you have an LBE installed? Wouldn't that take precedence over the CV, even if the're both in series with each other? Strange....</strong><hr></blockquote>
I thought that the klr could go into limp mode for several faults beyond just overboost protection.
Doesn't the lbe just provide the initial delay of air pressure, and then just opens and acts as a slight restriction. I assume that this restriction is what is causing it to boost to .4 bar instead of .2 bar.
[quote]<strong>To test if the altitude sensor is causing this issue, disconnect it from DME line #30. The DME leans out the mixture 6.3% when the altitude compensation is triggered. That might be a bit too much for the altitude where you were, maybe causing a lean mixture? Or the chips you have may have a different value for altitude compensation.
Don't know where you would go to test this anyway... Mt. Hamilton?</strong><hr></blockquote>
Thanks for the information. Beyond the DME leaning the mixture out 6.3%, does it do anything to timing or tell the klr to adjust the boost level? Does the klr increase its knock sensitivity? On another note, does the klr, using its' internal map sensor, tell the dme to vary the mixture even when off boost?
Thinking about it further, at WOT, the O2 sensor doesn't do anything. Further the air temp sensor sits in front of the turbo near the airbox along with the afm, and the coolant temp sensor wouldn't have any effect. The only thing that would tell the computer to go into limp mode would have to be the knock sensor. So, even though the mixture may be a bit rich, the main problem is likely the turbo is way past its efficiency range trying to go from .75 bar absolute to 2.0 bar absolute and it is superheating the air.
10-07-2002, 12:38 PM
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[quote]Originally posted by Richard Sandor:
<strong>8,000ft ???
It's not that you shouldn't be driving a car that high up, but honestly, I don't think Porsche ever designed the car with that kind of altitude in mind.</strong><hr></blockquote>
The highest elevation was actually 7,280 at the top of the Kingsbury grade near Heavenly ski area. Still, if you ever check out the Alps, there are numerous high elevation roads. I'm sure Porsche designed and tested the car to work at high altitude, but I bet most aftermarket manufacturers skipped this step. I suppose the extra efficiency available in the stock turbo is what allows it to operate at high altitude. When we ask it to crank out 2 bar absolute at high altitude, it just doesn't work.
A map based fuel injection system should be able to fully compensate for altitude off boost, but with the temperature measured before the turbo, it also couldn't see how much hotter the air is getting after the turbo
[quote]<strong>Secondly, If the altitude correction box and DME were any good, they would gradually lean out the mixture as you got higher - as opposed to applying one correction value over a fixed altitude.</strong><hr></blockquote>
Agreed. I wonder if anyone out there can tell us what more modern cars do to compensate at high altitude. What about turbo cars?
[quote]<strong>Whether the problem is porsche component specific or not - I dunno, but if you are driving that high up regularly, I would suggest looking into newer aftermarket components that correct gradually, with altitude.</strong><hr></blockquote>
Perhaps I need to reduce the maximum boost level at high altitude. I'm typically close to sea level, but Lake Tahoe is such a nice place that I may be inclined to spend more time there. Maybe I should buy one of the $15,000,000 estates on the Nevada side so I can take advantage of the tax advantages of Nevada.
<strong>8,000ft ???
It's not that you shouldn't be driving a car that high up, but honestly, I don't think Porsche ever designed the car with that kind of altitude in mind.</strong><hr></blockquote>
The highest elevation was actually 7,280 at the top of the Kingsbury grade near Heavenly ski area. Still, if you ever check out the Alps, there are numerous high elevation roads. I'm sure Porsche designed and tested the car to work at high altitude, but I bet most aftermarket manufacturers skipped this step. I suppose the extra efficiency available in the stock turbo is what allows it to operate at high altitude. When we ask it to crank out 2 bar absolute at high altitude, it just doesn't work.
A map based fuel injection system should be able to fully compensate for altitude off boost, but with the temperature measured before the turbo, it also couldn't see how much hotter the air is getting after the turbo
[quote]<strong>Secondly, If the altitude correction box and DME were any good, they would gradually lean out the mixture as you got higher - as opposed to applying one correction value over a fixed altitude.</strong><hr></blockquote>
Agreed. I wonder if anyone out there can tell us what more modern cars do to compensate at high altitude. What about turbo cars?
[quote]<strong>Whether the problem is porsche component specific or not - I dunno, but if you are driving that high up regularly, I would suggest looking into newer aftermarket components that correct gradually, with altitude.</strong><hr></blockquote>
Perhaps I need to reduce the maximum boost level at high altitude. I'm typically close to sea level, but Lake Tahoe is such a nice place that I may be inclined to spend more time there. Maybe I should buy one of the $15,000,000 estates on the Nevada side so I can take advantage of the tax advantages of Nevada.
10-07-2002, 01:03 PM
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[quote]Originally posted by Steve Lavigne:
<strong>I wish I had brough a led and a list of the klr error codes so I could see why it was going into limp mode.</strong><hr></blockquote>
I had the exact same problem on my car before I moved to standalone. It happened with stock chips and Autothority chips. If you shut down the car and restart it, it wouldn't show any error codes. I did manage to drive it while in limp mode to get it checked, and the only error code was "Low Boost". Didn't help at all.
<strong>I wish I had brough a led and a list of the klr error codes so I could see why it was going into limp mode.</strong><hr></blockquote>
I had the exact same problem on my car before I moved to standalone. It happened with stock chips and Autothority chips. If you shut down the car and restart it, it wouldn't show any error codes. I did manage to drive it while in limp mode to get it checked, and the only error code was "Low Boost". Didn't help at all.
