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Vanagon (Digifant) Air Flow Meter (AFM) Adjustment Procedure
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purplegodzilla
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PostPosted: Tue Jan 29, 2013 6:36 am    Post subject: Reply with quote

Great post. Thank you.
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Vwman55
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PostPosted: Sat Mar 30, 2013 4:50 pm    Post subject: Reply with quote

Should I see a steady 0.5 volts? Idle at 875 rpm, adjust co on afm and I get fluctuating from 0.5 to 0.8 volts. If I reduce the air it drops at some point near 0.
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denwood
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PostPosted: Sat Mar 30, 2013 5:14 pm    Post subject: Reply with quote

It will be steady if you measure o2 sensor voltage, disconnected from ECU. If you leave it connected to ECU, and your multimeter has an averaging function, it should average .5V.

An o2 sensor output oscillates rapidly when connected to the ECU because the ECU is varying injector pulse/duty cycle to toggle oxidative/reductive chemistry in the catalytic converter (that's a primary role for the o2 sensor.) So the ECU is reading o2 sensor voltage and constantly taking mixture above and below stoichiometric (.5 V). Unplug from the ECU, the computer knows this..and stops messing with mixture (therefore o2 reading is now steady) so you can set up the AFM and CO correctly.
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Vwman55
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PostPosted: Sat Mar 30, 2013 5:26 pm    Post subject: Reply with quote

What I'm seeing is with the o2 sensor disconnected. Volt meter connected to sensor and ground.
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Vwman55
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PostPosted: Sat Mar 30, 2013 5:26 pm    Post subject: Reply with quote

What I'm seeing is with the o2 sensor disconnected. Volt meter connected to sensor and ground.
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denwood
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PostPosted: Sat Mar 30, 2013 5:59 pm    Post subject: Reply with quote

Compression test ok? Is ISV unplugged? Anything causing poor combustion in in one cylinder or more would also create unstable readings. Vacuum leaks at injectors etc, same thing. What symptoms prompted you to adjust AFM?
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shadetreetim
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PostPosted: Sat Mar 30, 2013 11:29 pm    Post subject: Reply with quote

denwood wrote:
I added a dash gauge that monitors the o2 sensor signal


I kept thinking I wanted to add this voltage meter to my dash but had forgotten the details about it. Embarassed Checking out this thread tonight I re-read your post and now have a Lascar EMA-1710 Voltage Meter being shipped.

Cool stuff
Image may have been reduced in size. Click image to view fullscreen.


Thanks Denwood Applause Another gauge to obsess over. Laughing
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Vwman55
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PostPosted: Sun Mar 31, 2013 7:18 am    Post subject: Reply with quote

I had a bad ISCU. Got a good one and I am trying to set it up per the Digifant manual. I don't know what the PO did but, the CO plug was gone.
I want to know for myself that everything is base line. I been thru the checks of the system, wiring, FP pressure, etc, everthing checks out.
I have checked for vacuum leaks, didn't find any. I used a vac pump and sprayed carb cleaner around and there was no change in rpm.
I'm a little curois though why I can screw down both Idle and CO screws and still idle at 750 rpm's. I would expect the engine to stall.
I have considered it's time to send the injectors to Wicthhunter for cleaning.
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denwood
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PostPosted: Sun Mar 31, 2013 11:56 am    Post subject: Reply with quote

Screwing down idle (with ISV disconnected) should stall it. use the propane method and check for leaks (van running)at the throttle body, injectors, pcv boots etc. I tried a few methods, however the only one that caught the leaks was propane. Getting idle, co and AFM correct are impossible if there are vacuum leaks. Mine purrs like a kitten now. My issue was improperly installed injector o-ring seals. You may want to isolate pcv and ISV hoses to check for leaks there too.

Tim, that gauge is my favorite addition to the van. Using it you can visualize Digifant injection problems right away. Here's what it monitors:

1. Throttle body switches
2. Throttle off fuel cut (when slowing down with engine over 2k)
3. O2 sensor
4. Closed to open loop operation (coolant thermo sensor)
5 AFM operation
6. Full throttle enrichment.

I've found it super useful in seeing that AFM setup is correct, more or less by watching the needle. If it's flicking back and forth equally over center (.5V)you have it right. If it's biased right or left, you know the spring setting on Afm is not correct. Nice that it fits into an unused switch port too Smile
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Vwman55
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PostPosted: Tue Apr 02, 2013 4:51 pm    Post subject: Reply with quote

Used propane and no leaks found. I disconnected the brake booster vac, the evap return and evap control vac and plugged. Still no leaks. Vac gauge reads 13 hg and steady @ idle. What's the normal for valve adjust on the Vanagon? I have a Bay with hydro's the "book" says 2 turns, I've heard cold, warm, hot and everything in between. I set them cold @ 1.5 turns.
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MootPoint
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PostPosted: Thu May 16, 2013 9:05 am    Post subject: Reply with quote

I'm struggling with too-rich issues m'self. Can someone explain this "propane test" procedure? (It sounds like a good way to turn your Van into the Hindenburg.) My next step, with or without propane, is new injector seals. In any case my O2 voltage output won't stabilize with any adjustment of the AF screw.
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countrybicycle
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PostPosted: Thu May 16, 2013 8:20 pm    Post subject: Reply with quote

I would like to install one of these meters like Tim did to monitor the O2 but is it really possible to monitor all those other parameters listed below? How do you do this? Is the gauge wired to all these switches and sensors and you use a 6 position dial to change inputs as needed?

Tim, that gauge is my favorite addition to the van. Using it you can visualize Digifant injection problems right away. Here's what it monitors:

1. Throttle body switches
2. Throttle off fuel cut (when slowing down with engine over 2k)
3. O2 sensor
4. Closed to open loop operation (coolant thermo sensor)
5 AFM operation
6. Full throttle enrichment.

I've found it super useful in seeing that AFM setup is correct, more or less by watching the needle. If it's flicking back and forth equally over center (.5V)you have it right. If it's biased right or left, you know the spring setting on Afm is not correct. Nice that it fits into an unused switch port too Smile[/quote]
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shadetreetim
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PostPosted: Thu May 16, 2013 11:31 pm    Post subject: Reply with quote

zoovegroover wrote:
is it really possible to monitor all those other parameters listed below? How do you do this? Is the gauge wired to all these switches and sensors and you use a 6 position dial to change inputs as needed?

1. Throttle body switches
2. Throttle off fuel cut (when slowing down with engine over 2k)
3. O2 sensor
4. Closed to open loop operation (coolant thermo sensor)
5 AFM operation
6. Full throttle enrichment.



No switch needed, you're not looking for input from 6 devices. The meter simply parallel wires to the O2 Sensor. I would suggest a shielded cable. What denwood is describing is the ability to analyze these 6 settings/devices by observing the single meter.

For example, #2 Throttle off fuel cut (when slowing down with engine over 2k) is seen as 0 Volts as soon as you lift the pressure on the gas pedal. Apply light throttle again and it goes back to fluctuating above/below .5 volts.
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'89 Vanagon Bluestar/Country Homes 1.8T & .77 4th
'10 Wrangler 3.8 6SP Manual
'12 Ford E350
'12 Tiguan 2.0T 6SP Tiptronic - Lady Shadetree's
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countrybicycle
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PostPosted: Fri May 17, 2013 8:25 am    Post subject: Reply with quote

Thanks Tim - so with the gauge reading the O2 sensor, the other information would be interpretive? I think I can wrap my head around that.Regarding the connection at the O2 sensor wire...what does that look like? Does it happen where the green wire plugs into the wire going to the O2? You use the shielded wire to get out of the engine compartment and then you can switch to regular stranded?

shadetreetim wrote:
zoovegroover wrote:
is it really possible to monitor all those other parameters listed below? How do you do this? Is the gauge wired to all these switches and sensors and you use a 6 position dial to change inputs as needed?

1. Throttle body switches
2. Throttle off fuel cut (when slowing down with engine over 2k)
3. O2 sensor
4. Closed to open loop operation (coolant thermo sensor)
5 AFM operation
6. Full throttle enrichment.



No switch needed, you're not looking for input from 6 devices. The meter simply parallel wires to the O2 Sensor. I would suggest a shielded cable. What denwood is describing is the ability to analyze these 6 settings/devices by observing the single meter.

For example, #2 Throttle off fuel cut (when slowing down with engine over 2k) is seen as 0 Volts as soon as you lift the pressure on the gas pedal. Apply light throttle again and it goes back to fluctuating above/below .5 volts.
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denwood
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PostPosted: Fri May 17, 2013 1:11 pm    Post subject: Reply with quote

That's correct...interpretive. The sensor wire up front essentially "t's" in to the green wire from the 02 sensor going to ECU.

1. Fuel cutoff - as Mr Shadetree tim describes above. Smile This also checks the TPS for correct "idle" operation as fuel cutoff will not work otherwise.

2. Full throttle enrichment - Floor it, 02 gauge holds steady at .8-9 volts.

3. Closed to open loop - as vehicle reaches operating temp, coolant temp sensor signals warm, engine goes open loop. 02 gauge shows this in by moving from a steady reading, to rapidly oscilating above/below .5 volts. A failed coolant temp sensor will defeat this behaviour.

4. AFM - if AFM is set correcly, as well as idle CO, you will see the 02 gauge bouncing with an equal bias above and below .5 volts. Anything rich or lean will skew this behaviour predictably.

The page on my old site on the topic: http://my.tbaytel.net/guskers/gauges.html

Cheers,
Dennis.
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Last edited by denwood on Fri May 17, 2013 1:24 pm; edited 1 time in total
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shadetreetim
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PostPosted: Fri May 17, 2013 1:18 pm    Post subject: Reply with quote

denwood wrote:
Mr Shadetree tim

2. Full throttle enrichment - Floor it, 02 gauge holds steady at .8-9 volts.

Cheers,
Dennis.


Who you callin' Mr, Mister? Laughing

Interesting about the FTE. On mine, and on a 2.2 WBXR I've recently ridden in, the gauge goes to zero for a few seconds when floored.
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Tim Potts

Doing my best every time I drive it to dispel the myth these Vanagons have to be slow!


'89 Vanagon Bluestar/Country Homes 1.8T & .77 4th
'10 Wrangler 3.8 6SP Manual
'12 Ford E350
'12 Tiguan 2.0T 6SP Tiptronic - Lady Shadetree's


Last edited by shadetreetim on Fri May 17, 2013 1:19 pm; edited 1 time in total
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shadetreetim
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PostPosted: Fri May 17, 2013 1:18 pm    Post subject: Reply with quote

oops. Double post.
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Tim Potts

Doing my best every time I drive it to dispel the myth these Vanagons have to be slow!


'89 Vanagon Bluestar/Country Homes 1.8T & .77 4th
'10 Wrangler 3.8 6SP Manual
'12 Ford E350
'12 Tiguan 2.0T 6SP Tiptronic - Lady Shadetree's
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denwood
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PostPosted: Fri May 17, 2013 1:43 pm    Post subject: Reply with quote

I am describing Digifant II there, but I believe WBX full throttle ecentric would result in the same 02 gauge behavior.
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countrybicycle
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PostPosted: Fri May 17, 2013 2:22 pm    Post subject: Reply with quote

Sorry - forgot to mention that my case refers to an early 85 1.9

denwood wrote:
I am describing Digifant II there, but I believe WBX full throttle ecentric would result in the same 02 gauge behavior.
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andrewnorway
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PostPosted: Fri Sep 13, 2013 5:16 am    Post subject: Reply with quote

Hi, and thanks for all this fantastic info. I have an ambulance with MV and digifant which has gradually developed Vanagon Syndrome. Jumping from closed to open loop and back again especially in low gears and during acceleration. Worse when hot, but we're talking about 2-3 hours of driving. Temp.sensor has been replaced, likewise O2 sensor, but to no avail. I just don't know where to begin. Connections and leaks checked, all seems ok...
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