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

[Alexei Pavlov]

Hi, 

I assume you speak about the flap AFM.


cice at trub.com wrote:
> 
> I'm very confused by something and I'm hoping someone can clarify...
> 
> Am attempting to replace the AFM with a MAF sensor (using a signal
> conditioner)...and am not sure how/where to send the voltage.
> 
> Pin 6 - as far as I can tell is ecu ground
> Pin 7 - afm signal voltage to ecu (at idle, 3.2v across 6&7)
> Pin 9 - 12v supply (w/o car running)
> Pin 8 - what the frick is this?  7.6v?

I beleave it's the CO correction pot (A/F rate). As ECU does not
have loop back infos (lambda sensor) it needs to be adjusted to know
when the reference A/F is maintained.
This is a pot connected in parallel to the AFM pot with the middle
available at this pin.


> (36/39 = fuel pump, 27&6 is air temp...those are easy)
> 
> If I simply send signal down pin 7 (leave 8 and 9 disconnected), the ecu
> is clearly unhappy with this and just dumps gas pretty much w/o regard
> to the signal voltage on 7.
> 
> I've read in various places that the afm voltage is corrected for dips
> in battery voltage.  If I put a 200 ohm resistor between pins 8 & 9, I
> can get the car to run, but it's now way lean.
> 

Correcting the flap AFM signal is not simple at all, I'm working
on since the end of last year. You can not modify it by just putting
resistors in series or parallel.
The L-Jetro AFM has a sqrt(flow) output voltage function. In fact I'm
even not sure it's sqrt() and not any other similar function, none
information can be found today (I've searched a lot).


> Anyone have any insight into the relationship between these 4 pins?  If
> I plug the afm back in, it's all magic...3.2v between 6&7.  But put 3.2v
> down 7 w/o 8&9 and chaos ensues.
> 
> Chris
> --
> Chris Ice                    "Laugh'a while you can, Monkey Boy."
> http://www.trub.com/                               - Dr. Lizardo
> 
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