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Replacing and tuning 1.9L (Digijet) AFM
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kenoravsky
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Joined: November 17, 2015
Posts: 67
Location: Billings, Montana
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PostPosted: Fri Aug 21, 2020 12:58 pm    Post subject: Replacing and tuning 1.9L (Digijet) AFM Reply with quote

After a few years of asking dumb questions and getting smart answers, I am proud to say that I can finally contribute something to the Samba.

A few years ago Quixotix gave us this very useful post about tuning a 2.1L AFM:

https://www.thesamba.com/vw/forum/viewtopic.php?t=...mp;start=0

Unfortunately, I have a 1.9 Digijet, and I had a slightly different situation: My van ran pretty well, but had some serious dead spots on the AFM carbon tracks, which took some nursing the throttle at certain speeds and loads. Tencentlife's 5 volt testing procedure confirmed this. I found a used AFM with good carbon tracks that I was able to clean up. It tested perfect electrically. However, the wiper position was a bit different, and I couldn't tell if the spring had a different adjustment. The idle mix screw was different too, but that was easy to assess and change.

Here's my adjustment (2.1L to 1.9L) to Quixotix's procedure:

1) O2 sensor only has one wire, so the correct wire to use is obvious.
2) There is no idle control valve, so nothing to disconnect there.
3) Temp sensor II is on pins 2&7 instead of 6&10.
4) If you want to compare how one AFM spring setting compares to another's, remove the AFM from the vehicle and bench test it with a shop vac. I just sealed up everything and gave the AFM full shop vac vacuum, which ran about 3/4 up the scale. I marked the wiper positions on both AFMs and they were identical.

Bottom line: Better idle, better acceleration and a bit more power. I'll check on fuel economy over the next few tanks. Now I can rebuild or get the old AFM rebuilt and have a good spare.
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tencentlife
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Joined: May 02, 2006
Posts: 9996
Location: Abiquiu, NM, USA
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PostPosted: Fri Aug 21, 2020 2:02 pm    Post subject: Re: Replacing and tuning 1.9L (Digijet) AFM Reply with quote

Just don't vacuum the shop between tests!
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Please don't PM here, I will not reply.

Hmmm, provincial much?:
Quote:
"I wouldn't go much on whats written on the samba, they love a "theory" and rarely ask any Europeans what is actually correct."
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kenoravsky
Samba Member


Joined: November 17, 2015
Posts: 67
Location: Billings, Montana
kenoravsky is offline 

PostPosted: Fri Aug 21, 2020 2:16 pm    Post subject: Re: Replacing and tuning 1.9L (Digijet) AFM Reply with quote

Yes, we must be good scientists. I did these tests one after the other. Any extra junk in the shop vac or on its filters would change its vacuum.
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