What Should I Change???dfi


mean old man
May 25, 2001
I have a DFI with 55# inj. TE-63 mild cam etc. I just moved to Colo. The track is at 5800'. What changes do I need to make to my 55# program for this altitude? Take out 10% ,20% of the fuel add a bunch of timeing? One of you programers must know what to do.
I don't think you need to change anything in the base fuel table. Since that table is based on MAP, and it automatically recognizes that you have a lower MAP at that altitude, it should be self compensating in that regard.

I'm sure other changes would be useful though, esp. timing, but I'm pretty ignorant on that topic, sorry.

I disagree. With that much altitude I would try and gradually correct for the altitude. Less air means you need less fuel as well.

No matter what altitude you are at the air/fuel ratio does not change. You still need a given amount of air with a given amount of fuel. 14.7 to 1 the street. I am told with race gas 12.5 to 1.

The real help to doing this is having some way to monitor the EGT. That will tell you if you are rich or lean.

The DFI can comensate for MAP but once you are in open loop ( I cant remember if it is open or closed loop, sorry) the computer simply puts the amount of fuel you have placed in the cell on the map. So you could be running very rich at that altitude.

Sea level air is very dense, mountain air is thinner. If you use the same fuel map for the mountains as you do the beach( do they have those in Colorado?) there is a major difference in the actual amount of air you are stuffing in the cylinders.

Hope this helps.:)
While that is true, I look at it this way:

An n/a car at the beach at WOT might have a MAP at 100 kPa, so the when it wants to see how much fuel to inject it goes to the 100 kPa cell and the rpm and looks up that value.

Same n/a car in the mountains at WOT might have a MAP around 90 kPa, so the when it wants to see how much fuel to inject it goes to the 90 kPa cell and the rpm and looks up that value instead.

Or interpolates between the applicable cells to get those values, but you get the point.

And the same thing happens on a turbo car, 20 psi boost will have a different MAP at the beach than it will in the mountains.

Now if the cells at 100 kPa were dialed in pretty good but the ones at 90 kPa were not, then there is some tuning to do. But the fact remains that the system recognizes automatically that the air pressure is lower and will start looking in different cells to get different fueling. The amount of tuning will depend on how well those cells were dialed in before.

You are right, the MAP changes and the ECM looks for the appropriate cell.

What do you do when you are in a closed loop mode. The ECM puts the amount of fuel you have entered for that cell regardless of what MAP sensor reads.

We buy these ECM so we can fine tune them in the first place.
You da man, Turbo.