24V default AFM arm position - Alfa Romeo Bulletin Board & Forums

 
LinkBack Thread Tools Display Modes
post #1 of 9 (permalink) Old 03-10-2017, 08:20 PM Thread Starter
Registered User
 
Join Date: Aug 2015
Posts: 46
24V default AFM arm position

When I acquired my 164 18 months ago it had a multitude of air leaks. All have now been fixed. I'm certain the previous owner had the air flow meter adjusted to compensate for the leaks. Annoyingly the arm of the AFM has been moved. I completely appreciate this is factory set and should never be touched. Can someone please advise me of the correct REST position for the arm in the 24V car? Here is my AFM attached. Should the arrow be right at the edge of the resistor strip or part way along?
Attached Images
 

1993 164QV
DanNZ is offline  
Sponsored Links
Advertisement
 
post #2 of 9 (permalink) Old 03-11-2017, 08:15 AM
Registered User
 
goats's Avatar
 
Join Date: Jul 2006
Location: san diego CA
Posts: 3,663
Dan there's no real answer. The AFM is individually laser trimmed to achieve the resistance curve needed. The wiper is set in mfg, then moved thru its arc and laser cuts on the resistors included in the circuit are made. Your best bet is a used, unmolested replacement
goats is online now  
post #3 of 9 (permalink) Old 03-11-2017, 09:03 AM
But Mad North-Northwest
Platinum Subscriber
 
Gubi's Avatar
 
Join Date: Sep 2003
Location: SF Bay Area, CA
Posts: 8,356
As far as I know the AFM is only adjusted by changing the spring tension, not moving the arm.

Are you having some specific running problems that you think could be related to the AFM?

Tom

1991 Spider
1963 Giulia Spider (1750 engine)
Gubi is online now  
 
post #4 of 9 (permalink) Old 03-11-2017, 11:40 AM Thread Starter
Registered User
 
Join Date: Aug 2015
Posts: 46
Yes definitely still have an AFM problem, the occasional flat spot on moderate acceleration. I can improve it by incrementally reducing the spring tension but then the car ends up running too rich. I'm certain all other possible causes have been addressed - fuel pressure, air leaks, plugs, coils, various connectors etc. I was hoping someone had opened theirs and could give some indication as to where the wiper arm rests when the engine is off (at least on their meter) I figure they are all made by Bosch and the rest position at least might be common between meters. I'm certain the wiper arm position was fiddled with on mine, when I got the car it was resting right off the end of the resistor strip!


Sent from my iPad using Tapatalk

1993 164QV
DanNZ is offline  
post #5 of 9 (permalink) Old 03-11-2017, 03:50 PM
Registered User
 
Join Date: Jan 2007
Location: UK
Posts: 860
If it helps, I am planning to strip a 164 twinspark AFM to try sliding the carbon track/pcb up a little to give it new bit of track to run on - as a test to attempting the same thing for my 164 24v. Have been putting it off but heard good things about the procedure - if done correctly - and will post pics when do it. Give me a couple of weeks.

Cheers,

Richard
richardbradford is offline  
post #6 of 9 (permalink) Old 03-11-2017, 04:41 PM Thread Starter
Registered User
 
Join Date: Aug 2015
Posts: 46
Thanks, that would be very helpful! I've done the same mod as you - it definitely helped. Take your time, best to take the circuit board right out of the AFM before you make the holes bigger.


Sent from my iPhone using Tapatalk

1993 164QV
DanNZ is offline  
post #7 of 9 (permalink) Old 03-11-2017, 06:34 PM
Registered User
 
Join Date: Jan 2007
Location: UK
Posts: 860
Quote:
Originally Posted by DanNZ View Post
Thanks, that would be very helpful! I've done the same mod as you - it definitely helped. Take your time, best to take the circuit board right out of the AFM before you make the holes bigger.


Sent from my iPhone using Tapatalk
Good to know, thanks. Will be marking everything so can return to original positions in worst case.
richardbradford is offline  
post #8 of 9 (permalink) Old 03-12-2017, 03:52 PM Thread Starter
Registered User
 
Join Date: Aug 2015
Posts: 46
I seem to have made some progress. I set the arm default position to the very edge of the resistance strip which helped a lot, then I slowly increased the spring tension one stop at a time (ie rotating the wheel clockwise). It was initially running far too rich. Reached a point were it seemed to be running well (tested when cold and warm) then went one stop further which gave me slightly rough gentle acceleration. Figured I'd likely set too lean, so one stop back and all seems good. My neighbor has an old exhaust gas analyzer - so we may try that while driving.

If you are interested, these links are very helpful in diagnosing AFM faults (but not at resetting a messed with meter like mine!). The 24V 164 has the same meter as the later Porsche 944, so the input voltage is 5V (as per the document in the link). I appreciate this info is in the electrical manual on the 164 car disc, but I like the way this author has set it out... Turns out my AFM is good electrically, a nice smooth increase in voltage as the arm is moved. Make sure to disconnect the AFM when measuring the resistance of the temp sensor or you will get a dud result.

Electrically testing the AFM:
Air Flow Meter (AFM) Operation and Testing

If you are opening the AFM to modify it, it's easy to measure the voltages while the meter is in the car and connected, just use alligator clips on multi-meter leads attached to the inside of the AFM.

This details rejuvenating a worn AFM by bending the wiper arm- I think moving the circuit board by drilling larger holes is a better bet!
Air Flow Meter (AFM) - from "The 944 Motronic DME" by FR Wilk

1993 164QV

Last edited by DanNZ; 03-12-2017 at 03:55 PM.
DanNZ is offline  
post #9 of 9 (permalink) Old 03-12-2017, 04:23 PM
But Mad North-Northwest
Platinum Subscriber
 
Gubi's Avatar
 
Join Date: Sep 2003
Location: SF Bay Area, CA
Posts: 8,356
Sounds like you're getting close. If you have a digital voltmeter you can tune it without a gas analyzer. You clip a wire to the O2 meter connector (without disconnecting it from the harness) and run it to a voltmeter in the passenger seat.

See step 12 in the L-jet procedure below for details.

L-jetronic Fuel Injection Technical Troubleshooting Article

Tom

1991 Spider
1963 Giulia Spider (1750 engine)
Gubi is online now  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Alfa Romeo Bulletin Board & Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome