AFM air flow meter flap not operating correctly???

kdawghuntnfish · 10-02-2006, 06:50 PM

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.

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kdawghuntnfish · 10-02-2006, 07:12 PM

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

.

InternetRoadkill · 10-02-2006, 07:50 PM

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.

motoriderbc · 10-02-2006, 10:41 PM

Quote:

Originally Posted by kdawghuntnfish

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

.

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.

kdawghuntnfish · 10-03-2006, 03:28 PM

Quote:

Originally Posted by motoriderbc

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.

4Crawler · 10-03-2006, 06:02 PM

AFM test procedure from the FSM:

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

10-02-2006, 07:12 PM	#2 (permalink)
kdawghuntnfish Registered User Join Date: May 2006 Posts: 121	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 . __________________ Kevin 1990 Toyota DLX, rebuilt 3.0, manual, centerforce clutch, 3 inch BL, 4.56 gears, Firestone Destination M/T 33x12.50, Pacesetter exhaust, Taurus fan mod 1996 Dodge 2500, Cummins Diesel, 5 speed manual custom exhaust 1961 Chevrolet Impala- Just started off frame restoration. 1994 Jeep Grand Cherokee 4.0, Auto, stock

10-03-2006, 06:02 PM	#6 (permalink)
4Crawler Contributing Member Join Date: Jun 2002 Location: SF Bay Area, CA Posts: 7,832	AFM test procedure from the FSM: http://www.4crawler.com/4x4/CheapTri...tml#AFMtesting __________________ 1985 Toyota 4Runner SR-5, 22REC engine, dual t-cases, 4.88 gears, dual ARBs, 33x10.50 BFGs or 35x12.50 MTRs r.c.brown@ieee.org TruckEditor@tlca.org Project: 4Crawler 4Crawler OffRoad Gettin'Off 4WD Club

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10-02-2006, 07:50 PM	#3 (permalink)
InternetRoadkill Registered User Join Date: Jan 2006 Location: San Antonio, Texas Posts: 941	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.