Hi,
I am working on a 90 3.slow. I have been working trying to figure out a code 25 and 26 indication on my ECU. The only indication I have noticed in performance is that early in the morning is seems that the engine is lower in power than after it has warmed up outside. I decided to check the AFM since I noticed a noise like the door flapping shut or opening hard when I increased idle (gunning the motor). I checked ohms and everything checked fine except the Fc - E1 connection that should show infinity but it shows an open circuit. I checked some other posts and found this controls voltage to the fuel pump. Has anyone else had this problem, if so, what were the symptoms? My guess is there is something mechanically wrong with the door/shaft and it is not in the position the potentiometer is telling it to be in?

Just wanted to check before I spent the $$$ on a new AFM.

 

Did some more checking and with the AFM door manually opened and OHM readings were correct. Does anyone know if this is this correct: AFM door closed Fc - E1 circuit OPEN, AFM door open Fc - E1 circuit closed with no resistance? The Haynes manual does not specify .

 

I don't have the service manual handy to check what it should be. But I can tell you that there's a good chance the flapper door is simply dirty from corrosion.

You can check for this very easily by moving the vane with you fingers and feeling its motion. It should move smoothly with no sticky spots or grindy feeling. If it's not moving freely, don't panic. They can be repaired. I repaired mine and it's working like new.

 

That's normal. That circuit turns "ON" the fuel pump as soon as the door moves. It's designed that way so the fuel pump never runs without the engine running.

 

I was assuming the same thing. Thanks for verifying my assumption. The Haynes manual is then indeed incorrect in the testing procedure for the fuel pump circuit on the AFM. GO FIGURE.

 

AFM test procedure from the FSM:

http://www.4crawler.com/4x4/CheapTri...tml#AFMtesting