HOW TO TEST THE AFM SWITCH

[blusmith]

Hi- some pregress from having a no go motor and no fuel. I figured that PO had bypassed verything and plugged fuel pump into a hot circuit somewhere-- I can now get my 82 engine running after the rebuild by powering the fuel pump directly off the Igtn circuits and everything seems Dandy (phew!) How can I work out whether it's the relay set that is faulty or the AFM switch that controls the relay . Thanks Chris

[spider2081]

I think the best way to check the switch is to remove the black plastic cover on the AFS. You can then see the switch contacts and how they operate as the air flow door moves. With the cover off you can measure the voltage into and out of the switch right at the switch. Also you can rotate the AFS with your finger. With the ignition switch in the "start or run" position you should hear the fuel pump relay click and the pump run when the AFS arm moves a little off it's stop. Hope this helps

[blusmith]

Thanks for that . Will report on outcomes! Chris

[wizard124]

From a different post:

Terminal 15 of the ignition switch stays hot in RUN and and Start (pink/black wire to relay connection 86c). This wire powers the power control relay in the relay set. When closed, this relay energizes the injectors and ECU. Since your engine starts, this power control relay is working.

Once the key is out of the Start position, terminal 50 is cold (red/black wire to terminal 86a). 50 powers the fuel pump relay and cold start circuit. With the engine running and air being sucked through the Air Flow Sensor, its closed switch now energizes the fuel pump relay. The same power control relay is still closed that powers the injectors and ECU.

Since you have now swapped the relay set, I'll try to convince you to do the diagnostics I supplied earlier. The black plastic cover of the AFS is stuck on with silicone and removes easily. Inside you will see the contacts that should close with the slightest movement of the flap. If the flap is stuck or the contacts worn or mis-aligned, the fuel pump does not run and the engine quits.

[RRoller123]

FWIW: You can just see the rubbing marks where the door was dragging on my AFM in this picture. Some very slow and methodical sanding eventually freed it up.



In this pic you can see the 2 worn tracks on the Thick Film Resistive area. The bolt can be loosened and the arm lowered a little on the shaft, to force the wiper further out onto the TF into a fresh contact area.

[blusmith]

Thanks for the pics and advice
I was reluctant to open the AFM and thought that doing the ohmeter test was enough -- but will have a go

[narfire]

A pic of mine I took on Friday after moving the pins to a cleaner section of track.
Took the car out this afternoon and way better with idle and engine is smoother at lower rpms. I have brakes now after swapping out the booster as well.

I believe the silver arm is holding the fuel pump circut open. When the flap moves from cranking the arm moves, closes and pump is acitvated... perhaps the real experts will chime in...
Chris