RomRaider

Well the system I'm going to try to build would use a separate temperature probe, probably hooked up to one of the TGV sensor inputs, or wired into the stock IAT wiring.

I wouldn't bother trying to rip the stock thermistor out of the MAF housing. I can only imagine...

edit: nevermind

you could also use the input for the rear O2 sensor. that might be the way to go cause some people may want the ability to switch between MAF and SD with out having to rewire sensors.

http://www.romraider.com/forum/viewtopic.php?t=2046

Yes I cross posted. This is the Speed Density in action

wow, that all seems to make sense. but it also seems to too good to be true.

also i bet the reason it wouldn't run when you disabled the CEL for low MAF input was because the ECU relys on that CEL to trigger Speed density, otherwise it keeps trying to run normaly useing MAF but since its not reading any air flow its not running.

I have about 80 hours of operation with an STI engine from Eggenfellner. They originally tried to run the MAF in a turbulent blow through location and of course it did not work, so they unplugged it. Then someone decided to place a seperate IAT probe in the same location, right before the throttle body and after the intercooler.

I have converted by engine back to turbo from supercharged and this gives me the ability to put the MAF back into the system where it belongs, up close to the air filter via a short ram intake kit. Now I am not sure what to do with that IAT probe that is still sitting up near the throttle body. It originally came located up in front of the air filter (From Eggenfellner, not sure about the car applicaiton).

Can anyone tell me if this probe has any real effect on the engine tune, and if the MAF IAT is used along with the seperate probe input?

Also, I would like to know that the ECU will return to the fail safe tables it has been running on for the last 80 hours, in the event of an MAF failure. I have read that this is triggered via the CEL. Can anyone verify this?

I was thinking of inserting a disconnect switch to the power or sensor wire for the MAF so I couild force fail safe as needed, but if the CEL triggers fail safe then this may not be needed. Looking for the best reliability in making enough power to stay airborne...

Randy

The MAF high and MAF low CELs trigger the failsafe to use MAP. But you shouldn't get these unless you have an electrical problem. I don't think a working MAF (even if it is put in a poorly designed intake) will read out of range. Valid range is like 0.2v to 4.92v. Normal operating voltage is about 0.8v to 4.4v for a stock car.

As far as the extra IAT probe, well, the stock ECU doesn't have an extra input for an extra IAT probe. We probably couldn't tell you what it is used for or how it was integrated into your engine management system. Sure this is just a factory ECU controlled system? You can't just add a second IAT. It is possible on your harness the stock IAT is just cut out and your extra IAT is wired in its place. But we're not going to be able to determine that for you.

Thanks for the response Freon.

I definitley have the stock ECU, a 2004 version on a 2005 engine, but the harness has been hackep us a bunch to make it work in the airplane. I guess I will have to do some research to find out where that extra IAT proble came from and what effect it might be having, if any. I do have the normal MAF connector that has just been hanging out waiting to be put to use and it has not been hacked as nearly as I can tell.

Any idea which wires of the 5 at the MAF connector would be best to use for a sure fire method of forcing fail safe via a disconnect switch?

I assume the shielded wire is for the signal. I guess it would certainly trigger voltage low if I cut the power to it...

Randy

Freon,

I got the IAT business nailed. Eggenfellner had hacked the IAT off of the MAF back in the harness somewhere. With the MAF connected and the seperate IAT disconencted I got P0113 Intake AIr Temp High, plugged it back in and got a clean scan!

Apparently they purchased a seperate IAT probe and hacked it in.

Do you think getting IAT after the intercooler and just before the throttle body will cause any problems, or is that ideal?

Randy

it is a better location than pre-compressor...

-ken

Hard to say, too much stuff unknown with how your airplane setup is configured and tuned.