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Old 07-18-2002, 08:14 PM   #1
JaMa
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Join Date: Mar 2001
Location: Centennial, Colorado
Default Link Ambient Air

OK, so after MUCH tweaking and some good advice from a couple of guys with the Link computer in South Africa, I managed to get the problem of my car dying when it is 90+ degrees outside solved!!!

The problem was this: hot restarts with high outside temps cause negative throttle response and a stalled car. From talking to some people, datalogging, and carefully watching my gauges while the problem was occurring, I figured out the following:

When engine temp is 88 degrees C or greater, the Link goes into "fuel mode 2" which is a conditional open loop mode which is sampled every 2 minutes by the ECU based on engine temp and a corresponding Inlet Air Temp which must be 60 degrees C or better to trip the software switch. So, in this mode there is a setting called "Ambient Air" on the main fuel menu which has a value that can range from 0-100. This value, when mode 2 is engaged on the Link, REMOVES the appropriate amount of fuel from the car when the temperature is high. So, if you are in a zone with fuel of "97" and you have Ambient Air set to "15" your real fuel value at that temperature in that cell is 97-15 = 82. It also retards timing slighty by the same percentage so that detonation will not occur with the fuel being pulled back.

The guys in South Africa say there is some Link documentation out there somewhere on the net but that it is wrong and that the real functionality is what I stated above.

Now, I had to go to a LOT of trouble to get this information, so I am hoping it helps someone or is at least interesting for all you Link people out there to know about.

Cheers and happy tuning,

JaMa
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Old 07-18-2002, 08:23 PM   #2
davidm_sh
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Default

WOW that is some great stuff. I have only one question however. At first I thought, why would you want to pull fuel out? Becuase it seems you would want the same or little more fuel to cool down things a bit to compensate for the temp. But I guess they are assuming two things:

1) That the intake charge temp is hotter from hotter air (duh), less effecient intercooling, and therefore is less dense = less fuel needed?
1) And you will probably keep your duty cycly on your boost control the same and thereby that also adds to less boost on hotter days too.

Just trying to understand this a bit better.

Thanks again Jama
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Old 07-18-2002, 08:55 PM   #3
JaMa
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Default Less Air

Yes, hotter air is thinner air and at this altitude that makes a bigger difference. Plus, I already run a bit rich which means I need to compensate even more when its hot.

And yes, when its this hot out I only run 16lbs of boost because I dont want to shell my engine by making an already hot unit run hotter.

Plus, I dont care what anyone says - the VF30 is not a cool running turbo. Get 20lbs going through that thing and its hotter than hell.

JaMa
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Old 07-18-2002, 09:25 PM   #4
davidm_sh
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Well you also have to consider that if you are running the VF30 at 20lbs of boost up here then you have to remember that it has to work about 20% harder at 6000ft. (figure NA cars lose about 3%/1000ft. becuase ~3% less air/1000ft you go up) above sea level to get that.

So 20% of 20lbs is about 4lbs of equivalent spinning to so it would be like making 24lbs at sea level. Maybe my logic is flawed but I think you get the general idea .
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Old 07-18-2002, 10:37 PM   #5
JaMa
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Quote:
Originally posted by davidm_sh
Well you also have to consider that if you are running the VF30 at 20lbs of boost up here then you have to remember that it has to work about 20% harder at 6000ft. (figure NA cars lose about 3%/1000ft. becuase ~3% less air/1000ft you go up) above sea level to get that.

So 20% of 20lbs is about 4lbs of equivalent spinning to so it would be like making 24lbs at sea level. Maybe my logic is flawed but I think you get the general idea .
Yep I think thats basically the problem - not a big turbo and it is spinning really hard to make up for our useless air.

Still, I dont think I could stand more lag than I have today, even though I have a big Garrett hybrid on the way to try out... (evil grin)

JaMa
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