Here's a way to get the DFI 6 to work "right", IMO anyway. Please note: I haven't actually tried this, I do not own a DFI system, so use the following at your own risk. I may just be another internet expert that will show you how to blow up your car! That being said,
The air temperature correction table is % enrichment vs. air temperature.
The idea behind a speed density system is that you calculate air flow from the air density in the intake manifold. If the air density drops 10%, then air flow drops 10% and you need 10% less fuel. DFI 6 doesn't do this automatically (unless this table is filled out correctly). FAST does. I guess DFI 7 does, though I'm not sure. And of course the air temperature you are measuring needs to be the *manifold* air temp, not the outside air temp or the turbo inlet air temp.
If you figure up the air density at 80F and the air density at 120F you find that at 120F the density is 6.9% lower. Therefore if MAP, rpm, etc is all the same, the only difference is the air temperature in the intake, then with a 120F air temperature you'd need to inject 6.9% less fuel. Comprende?
So, what I would suggest, is you pick a "base" temperature. I'll use 80F. If the manifold air temperature is lower that this base, you need to add fuel to account for the higher air density. If the air temperature is hotter than this, you'll have to take fuel out since the manifold air density is lower.
Here's the numbers to use with 80F as the base point:
5F = 16.1%
20F = 12.5%
35F = 9.1%
50F = 5.9%
60F = 3.8%
70F = 1.9%
80F = 0.0%
90F = -1.8%
105F = -4.4%
120F = -6.9%
135F = -9.2%
150F = -11.5%
165F = -13.6%
180F = -15.6%
215F = -20.0%
250F = -24.0%
Now you still have to get your system all dialed in, so that you hit your desired a/f ratio over the range of operation of your engine. But once you do get it all dialed in, going from winter to summer (or vice versa) shouldn't affect your tune.
Initially I would expect the above to screw things up some, esp. this time of year, since it will be pulling some fuel out. If you find your manifold air temps are in the 130F range right now, better add 10% fuel to the main fuel map right off the bat before implementing the above! And if you find yourself rich or lean in spots after filling in this table, don't go back and change the air temp correction table to fix it, change the main fuel table instead!
Once you get it all dialed in again, it will be self compensating. Winter time comes, your MATs drop, and the fueling will automatically increase without you having to touch any maps.
Or, you could figure up the same table using todays temperature as the base (zero) point. Then you wouldn't have to mess with your main table at all, at least in the WOT regions. Probably have to take some out in the cruise and idle areas...
Anyway, I hope you get the gist of the idea and the ramifications involved.
Oh yeah, another point... the above values are based purely on air density differences. If you wanted to run a richer a/f ratio at a higher manifold air temp, those numbers have to be corrected some. Say for safety sake you wanted 11:1 if the air temp is at 165F, while 12:1 is good with the air temp at 80F, then the values in that table above need to be corrected for that. In that case the 165F correction factor, -13.6%, would need to be -5.8% instead, ie not pulling out as much fuel, so leaving the mixture a bit richer.
AND, I guess I should note that cold start problems would need to be addressed in one of the afterstart enrichment tables, rather than here.
I think that's it... let me know if you have any questions.
John
