Flight_951

I'm wondering what tool to use to adjust the CO screw on the AFM. The service manual doesn't seem to say it as far as I can see, but shows a t-handle wrench of some sort. I have a newly rebuilt AFM, not the original one. I don't want to put a screwdriver or allen head bit down that hole without knowing what's at the bottom... TIA

Charlotte944

If memory serves you can use a 6mm Allen wrench.

dgz924s

Are you using a CO tester to see what the air/fuel ratio is before you adjust it? Do not adjust without a way to check rich/lean. A 6mm 12pt allen key should fit.

Flight_951

So I went to sears and lowe's in a blizzard just now to find 12 point hex keys but no luck. :-) They have lots of the 6 point variety. Where do you guys buy your 12 point keys?

I know that the afm is set to .83v at idle at the dme right now (rich for old set of chips), so I want to turn it counterclockwise a half turn or so to lean it out a bit to about .6v. I'll check the voltage at the dme when doing this. The a/f gauge runs in the green too often right now, and the car bogs when it does this.

dgz924s

Flight.......Actually IIRC there is a place to buy the tool specified for the AFM. I will take a tour of my vendors to see which one had it. I think it was Baum Tools in Sarasota but not certain. I will get back to you soon! I am not even sure it is 12pt but I took a educated guess from memory.

Flight_951

That would be great Dal. Thanks!

Danno

"I know that the afm is set to .83v at idle at the dme right now (rich for old set of chips), so I want to turn it counterclockwise a half turn or so to lean it out a bit to about .6v. I'll check the voltage at the dme when doing this. The a/f gauge runs in the green too often right now, and the car bogs when it does this."

Be careful on which adjustment you're doing. It should be the recessed adjuster down the 1/2" hole on the side of the AFM that you see after popping off the small metal plug right? This is the barn-door bypass passage and is similar to the idle-speed adjuster that vents air around the throttle plate. This adjuster determines how much unmetered air is sent around the flapper-door without being measured. It will not change the AFM volage going to the DME. Thus, the computer wil still inject the same amount of fuel, but will be mixed with more or less air based upon the bypass-screw's setting.

That's how CO & idle-mixtures are set, by venting unmetered air around the barn-door, NOT by adjusting the AFM-voltage. Because the data-cell at 0.65v may actually have MORE fuel programmed in than at 0.85v. So make sure you're adjusting the bypass-passage, and NOT the spring-tension on the AFM.

Flight_951

Yes, I will adjust the afm bypass screw. I did want to measure the voltage at the dme for this adjustment if I can, because the CO sampling tube is not installed anymore (long story). Is there somewhere at the dme I can measure to set the CO?

Bri Bro

You might want to re-read Danno's post, adjusting the screw will not affect the voltage at the DME. You need to measure the CO before the cat to do the procedure in the manual. I doubt you have a gas analysis unit at your command to do this procedure. Turning the screw just allows more/less air to bypass the afm. You could put in another bung like the one used for an O2 sensor were the tube was, then put a plug in it when the testing is done.