Relocating the Plate in the FI AFC Unit

by Mark Strand

DETAILED INSTRUCTION FOR RELOCATING THE PLATE IN THE FI AFC UNIT

1. Remove the AFC from the van.
2. Carefully pry the black plastic cover from the aluminum AFC body. This may take some doing. First cut any RTV sealant from the cap and the aluminum body and then carefully slide a thin bladed knife in between the cover and the body working your way around the cover. Don't apply to much force, the idea is to pop the cover off, not cut if off. At some point with a little persuasion the cover will come off.
3. Orientation: looking into the unit you will see a white ceramic plate with black resistive nodes on it and the black resistive coating that the wiper blades travel on. From the white plate follow the copper wiper arm back to a black nylon part which indexes the wiper arm assembly to the spindle of the flapper assembly. The wiper indexing mechanism is attached via a screw to an aluminum clamp which in turn is attached to the flapper spindle.
4. Look at the black resistive layer that the copper wipers sweep across. In my case this area was so badly worn that both contact points had worn the resistive layer off for about a quarter inch exposing the white ceramic plate (I understand some wipers only have one contact point). Note which way you must move the plate in order to gain a good contact surface. If the black resistive layer appears to be in good condition skip the rest of the procedures and seal this unit back up.
5. Remove the two female lugs, these are from temp sender I. The wires of which come from under the white resistor plate.
6. Remove the four screws from the AFC electrical connector assembly and set aside.
7. Remove the assembly from the housing using caution as part of the assembly makes contact with both the wiper assembly and white ceramic plate.
8. Using an xacto knife, scribe the aluminum clamp on both sides of the black nylon wiper indexing mechanism so you can return this part to the original location upon reassembly.
9. Remove the screw from the indexing mechanism and careful remove the wiper index assembly. Set aside.
10. Remove one of the screws from the plate and make note of the orientation of the screw hole in the plate and the mounting hole in the AFC body as you will most likely need to relieve some of the material from the plate to facilitate the relocation. Remove the rest of the screws.
11. Remove the ceramic plate assembly. This unit is not static sensitive so you can handle it with your fingers just keep them OFF the resistive layer that the wipers rub against. One other note; DON'T fiddle with the two metal tabs that extend from and back into the metal plate. These make electrical contact to ground from the ceramic plate.
12. In my case the plate had to be moved far enough that I had to remove material from one side of the plate as well as elongate the mounting holes. I used a Dremel Moto Tool to do the work. Prior to cutting the material away I wrapped the unit in "Glad" wrap to protect the surface of the resistive layer from debris and finger oil. Work carefully and slowly so as not to develop a great amount of heat while grinding the material away. Remember, the tortoise won against the hair.
13. Test fit the assembly to make sure you have removed enough material.
14. Reassemble in reverse order and seal with a silicone sealant. I chose to use Permatex Ultra Gray because my past experience is that this stuff seals but if you need to get back into the part that's sealed it's not a royal PITA. Whatever you do use this stuff sparingly. You need to seal the unit but don't cake it on. NOTE: you must seal this up at some point because a small amount of air will leak through the bearings in the flapper spindle which will affect the mixture slightly.

That's pretty much it, however when I put mine back in service the motor leaned way out so I had to move the indexed thumb wheel as well. In the case of my unit when I loosened the spring the motor leaned even further. When I tightened the spring the fuel mixture became richer. I moved my thumb wheel five notches and everything came back into sync. You must use a CO meter in order to get this right otherwise you risk burning the valves with too lean a mixture. This is where the assistance of a trusted mech comes into play.