[Diy_efi] Re: Bosch L-Jet AFM question...

[Chris Ice]

Alexei Pavlov wrote:
> I'm really suprised by that product. They state they do elevation
> compensation.

Yes indeedy.  There is a pressure transducer visible inside the signal 
conditioner.

 > The problem is that the original ECU ALSO does this
> compensation (by using some not stupid tricks). To connect a MAF
> to an AFM based ECU one must de-compensate the MAF output, and for
> that he/she must know not only the air temperature, but also atmo
> pressure. And they don't state any usage of pressure gauges.
> Moreover, some cars (like Porsche) use pressure switches mounted
> apart the AFM, so they KNOW the atmo pressure.

Not that I'm an expert, but I doubt that this older system (Fiat/Lancia 
circa 1981) did this kind of elevation compensation inside the ecu or 
anywhere else.  I have personally built this installation (currently 
vane airflow), and there are no pressure sensors anywhere and I doubt 
there's one inside the ecu.  I could open one up and look visually as I 
have a spare ecu out of the car.

Air temp obviously has the air temp sender inside the afm, but the 
signal conditioner sends a constant 70deg F.  I *could* hook the 
original air temp sender up if I wanted to, but I doubt it's necessary 
as the MAF is already temperature compensated just due to how it works 
(ie. wheatstone based on temps).

Again, the goal to measure actual air mass not just volume (and in my 
case, remove the intake restriction [rumor has it ~12% power hit] and 
prepare for a turbo).

Chris
-- 
Chris Ice                    "Laugh'a while you can, Monkey Boy."
http://www.trub.com/                               - Dr. Lizardo



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