Date: Sun, 22 Jun 2014 18:23:09 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: AFM Idle Mixture Screw - loosey goosey
In-Reply-To: <615424333.127713.1403450800734.JavaMail.root@sz0094a.emeryville.ca.mail.comcast.net>
Content-Type: text/plain; charset="UTF-8"
Without the proper equipment you don’t adjust these, you tamper with them. If all is well and the O2 sensor is doing its job these should never need to be adjusted. That said, it is possible to turn them so far out (counter clockwise, open, leaner, etc) that you can get them above the thread and they will no longer do anything. You need to turn clockwise and push down slightly to re-engage the threads. It t does not tighten at some point then maybe the screw or body threads are stripped. If you have the means to set these up with all the other basic setting correct you should be able to trim between 1 and 3-4 turns.
To trim the poor man's way you can use the O2 sensor. Start engine and warm up, Get sensor hot enough to give reading.
With engine off, disconnect sensor and attach meter to sensor lead and ground. Set to a scale that will give a good reading at around .5vdc. start engine and run until you get a reading from the sensor. You may have to rev it up and wait a while. This is why the later vans use the heated sensors. Once working, at idle adjust the mixture trim to ~.3 to .7 volt. It may not stay exact. You want to get close. On the 1.9 to high and you will have a contributing factor for that idle surge. Stay on the leaner, (low side). This will be the basic setting.
Re-connect the sensor to the ECU and monitor with the meter. You should soon see the mixture being controlled, regularly going above and below the .5 volt threshold. If so all is working. Now keep in mind the goal is not for a steady reading. The system needs to regularly go below and above the ideal mixture for the 3 way catalyst to work. You are try to support both an oxidizing (lean, excess O2) reaction to burn of HC and CO and an oxygen deficient (rich) reaction to reduce NOx.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Skip
Sent: Sunday, June 22, 2014 11:27 AM
To: vanagon@GERRY.VANAGON.COM
Subject: AFM Idle Mixture Screw - loosey goosey
Need to know if the idle mixture screw is unrepairable...?
Reading an excellent thread on thesamba about AFM adjustments,
http://www.thesamba.com/vw/forum/viewtopic.php?t=356377&start=40
I decided to venture into the " my engine seems to run fine, but let me just make a few minor adjustments" realm and risk it all...
'84 Digijet, 2.2 L GoWesty kit into a 1.9 case.
My idle mixture screw seems to be stripped (doesn't tighten or loosen). From original position I turned righty 11 turns (to determine "tight point" and it was loose as a goose, still. I turned lefty a bunch of times, no change in depth of screw, no change in VOM (have the VOM attached to the O2 sensor end of the O2 wire (and to ground) +0.8 volts).
WAG: I wonder if the PO screwed down "below the threads", knocking off some "catch", thereby causing the screw to be turning freely below the female threads. Something like that? I have no idea why the screw appears to be without a female thread match.
Any way to get that screw working again? Anything to take apart to get at it? Anyone else experience this "loose as a goose" phenom? I can always order a new AFM (our friendly Pennsylvania vendor has them in stock). Or does anyone have a spare willing to let go of?
Thanks,
Skip
