What's up with this hole in the AFM flap?

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BellePlaine
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What's up with this hole in the AFM flap?

Post by BellePlaine » Wed Mar 18, 2015 8:05 pm

Two part numbers:
Bosch 0 280 200 012
VW 022 906 301 A
6-pin
Apparently it has been rebuilt/exchanged

I recently purchased this used AFM in hopes that it might be in a bit better condition that what I'm currently running. Here's picture.
Image

Two questions: first, see this hole in the flapper arm? Is it ok to leave it like that? Seems like an air by pass and could get me into too lean territory. My other AFM's are not this way.

Image

Second question; is it cool to use this Radio Shack Cleaner Lubricant to lubricate the potentiometer conducting strip? I sprayed some onto metal contracts and it made an aggressive "crackling" sound as it worked. Not sure if it would damage the potentiometer.

Image
1975 Riviera we call "Spider-Man"

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SlowLane
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Re: What's up with this hole in the AFM flap?

Post by SlowLane » Thu Mar 19, 2015 9:45 am

I'm pretty sure that hole should be covered with something like a flapper valve. I'm guessing that was Bosch's early attempt at implementing backfire protection in their AFMs. Later AFMs have a counter-balancing vane at 90 degrees to the measuring vane which immunizes the AFM against the effect of a backfire.

You might want to look into modifying your wiring harness to plug into a 7-pin AFM. If the resistance curve of the 6-pin and 7-pin AFMs are a match, then the only difference would be the TS1 sensor in the 7-pin, which you could safely ignore. It shouldn't be too difficult to remove the pins from a 6-pin harness plug and re-insert them into a 7-pin plug.

For lubricating the track, I'd recommend Caig FaderLube instead of that Radio Shack cleaner, which probably has some pretty aggressive solvents in it.
'81 Canadian Westfalia (2.0L, manual), now Californiated

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Jivermo
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Re: What's up with this hole in the AFM flap?

Post by Jivermo » Thu Mar 19, 2015 12:03 pm

That should work OK-it is safe for most plastics. DeoxIT is not for metal contacts. Caig makes the pictured lube for Radio Shack.

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SlowLane
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Re: What's up with this hole in the AFM flap?

Post by SlowLane » Thu Mar 19, 2015 2:41 pm

Jivermo wrote:That should work OK-it is safe for most plastics. DeoxIT is not for metal contacts. Caig makes the pictured lube for Radio Shack.
I beg to differ, sir. If indeed Caig is the supplier for the pictured Radio Shack Contact Cleaner, then it is probably a re-branded can of DeOxit "D-series", which is a contact cleaner intended to clean and de-oxidize metal contacts.

The FaderLube stuff I referenced is a tube of DeOxit "F-series", specially formulated to:
Caig's web site wrote:...improve conductivity and lubricate conductive plastic and carbon compound faders,
I believe the F-series Fader stuff would be a lot gentler on the AFM potentiometer track than the crackly/bubbly D-series metal contact cleaner. The D-series stuff would be great for cleaning/lubing the little metal-metal contact pads and pivots in the AFM, however. A pinpoint applicator is a lot more useful in this case than the spray can.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"Wisdom comes from experience. Experience is often a result of lack of wisdom."
- Terry Pratchett

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BellePlaine
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Re: What's up with this hole in the AFM flap?

Post by BellePlaine » Fri Mar 20, 2015 11:39 am

Thanks guys. I had a feeling that the Radio Shack stuff might have been too aggressive. So I bought this...

http://store.caig.com/s.nl/it.A/id.1748 ... tegory=293


Still wondering what the kind of effect that hole is going to have on my air/fuel mixture. And if I'm to plug it, how can I best make that happen without worrying about a screw/nut coming lose to get sucked into the engine.
1975 Riviera we call "Spider-Man"

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SlowLane
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Re: What's up with this hole in the AFM flap?

Post by SlowLane » Fri Mar 20, 2015 12:22 pm

Chris, I note that awhile back aircooledchris posted this: viewtopic.php?f=12&t=9076, to which you apparently responded.

The second photo clearly shows some sort of disc covering that hole, so the hole is clearly meant to not be open. If you were the lucky recipient of aircooledchris's AFM, I'll once again suggest you look into the feasibility of modifying your harness to use a 7-pin AFM. I think I have a 7-pin plug off of a junk harness that I can send to you if you like.

Or maybe it's possible to move the 6-pin connector pad assembly to a 7-pin AFM, if the contact pads line up.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"Wisdom comes from experience. Experience is often a result of lack of wisdom."
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BellePlaine
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Re: What's up with this hole in the AFM flap?

Post by BellePlaine » Tue Mar 24, 2015 10:45 am

That AFM that purchased from aircooledchris is in really good condition, and I bought it forgetting that I had a 6-pin harness. It's in such good condition that I wouldn't want to fiddle with it to try to make it fit a 6-pin.

If I was to rebuild my wiring harness, using your junk 7-pin plug, would I need to replace the ECU? I'm not even sure which ECU I have although I'm sure that I could find the part number.
1975 Riviera we call "Spider-Man"

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BellePlaine
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Re: What's up with this hole in the AFM flap?

Post by BellePlaine » Tue Mar 24, 2015 10:49 am

Also, back to the hole in the flap, I now know that it is a part of a back-fire valve. I'm missing the cover, post and spring. It's obvious that I should not run this AFM without those parts in place.
1975 Riviera we call "Spider-Man"

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SlowLane
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Re: What's up with this hole in the AFM flap?

Post by SlowLane » Tue Mar 24, 2015 2:44 pm

BellePlaine wrote:If I was to rebuild my wiring harness, using your junk 7-pin plug, would I need to replace the ECU? I'm not even sure which ECU I have although I'm sure that I could find the part number.
I don't think so, but we're entering uncharted territory here. The key thing is whether the resistance profile of the tracks in the 6-pin and the 7-pin AFMs are close to identical. If the part numbers for the resistor board are the same, then it's highly likely that they are. If not, then you'll need to measure the resistance segments on each board and see if they give the same resistance curve. Absolute resistances needn't match exactly, we're just looking for a profile for the voltage divider as a whole. If they are significantly different, then you would probably need to start thinking about finding a matching ECU and harness.

The idea here is to just use the parts of the 7-pin AFM that it has in common with the 6-pin AFM. The extra pin on the 7-pin is just there to connect to one side of the TS1 intake air temperature sensor, which the 6-pin AFM doesn't have, and which your ECU wouldn't know what to do with. So what we would be doing is connecting up the 6 wires from your harness to the matching 6 pins on the 7-pin AFM and leaving that last one unconnected.

I used to be all worried about making sure the ECU number matched the AFM number, until I looked inside the two AFMs which I purchased directly from Fuel Injection Corp. One is a Federal-spec, and one is a CA-spec for my year Vanagon. The part number on the resistor board is exactly the same for both of them, so obviously the only difference is in the spring tension and wiper settings.

You may not need to mangle your harness (although re-pinning the plug isn't particularly destructive, and it's revertible) if you have a junk 6-pin AFM lying around. You could build a 6-pin-to-7-pin adapter using the 7-pin plug and the 6-pin socket from the junk AFM. Minimal manglement.

Ratwell has some useful ECU part number info here.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"Wisdom comes from experience. Experience is often a result of lack of wisdom."
- Terry Pratchett

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Amskeptic
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Re: What's up with this hole in the AFM flap?

Post by Amskeptic » Thu Mar 26, 2015 10:24 am

SlowLane wrote:I'm pretty sure that hole should be covered with something like a flapper valve. I'm guessing that was Bosch's early attempt at implementing backfire protection in their AFMs. Later AFMs have a counter-balancing vane at 90 degrees to the measuring vane which immunizes the AFM against the effect of a backfire.
The pop-off valve was used to mollify the Type A Porsche 914/928 crowd which used to wreck their AFMs every morning as they rushed off to work at Goldman Sachs.

The 90* countervane has always been a part of the initial engineering of the AFM, it prevents a pressure differential on the incoming and outgoing sides of the flap in the air stream.
Note that the reduced pressure of a suddenly opened throttle plate could suck the flap open with a bang. The countervane merely provides an equal surface area exposed to the reduction in pressure on the other side of the pivot axis so that the only movement of the vane will be in response to actual air movement into the engine.
This countervane is as susceptible to damage from a backfire as the main vane. The pop-off valve was too expensive to install in mere Volkswagens . . . :cyclopsani:
Colin
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 93,996 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,113 miles

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SlowLane
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Re: What's up with this hole in the AFM flap?

Post by SlowLane » Thu Mar 26, 2015 1:00 pm

Amskeptic wrote:The 90* countervane has always been a part of the initial engineering of the AFM, it prevents a pressure differential on the incoming and outgoing sides of the flap in the air stream.
Note that the reduced pressure of a suddenly opened throttle plate could suck the flap open with a bang. The countervane merely provides an equal surface area exposed to the reduction in pressure on the other side of the pivot axis so that the only movement of the vane will be in response to actual air movement into the engine.
This countervane is as susceptible to damage from a backfire as the main vane.
I humbly stand corrected. :salute:
ColinPopOff wrote:The pop-off valve was used to mollify the Type A Porsche 914/928 crowd which used to wreck their AFMs every morning as they rushed off to work at Goldman Sachs... (edited-ed)
The pop-off valve was too expensive to install in mere Volkswagens.
Wait, I thought early injected 911s used K-jet (aka CIS). :scratch:
Whatever, from the looks of Chris's poor 6-pin AFM, the pop-off valve is just one more thing that can rattle loose to be ingested by the engine.

More to the point, what's your take on the feasibility of using a 7-pin AFM with the 6-pin system, as I've advocated to Chris above? Am I leading the poor fellow on a wild goose chase?
'81 Canadian Westfalia (2.0L, manual), now Californiated

"Wisdom comes from experience. Experience is often a result of lack of wisdom."
- Terry Pratchett

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Amskeptic
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Re: What's up with this hole in the AFM flap?

Post by Amskeptic » Fri Mar 27, 2015 9:40 am

SlowLane wrote:
Amskeptic wrote:The pop-off valve was used to mollify the Type A Porsche 914/928 crowd which used to wreck their AFMs every morning as they rushed off to work at Goldman Sachs...
The pop-off valve was too expensive to install in mere Volkswagens.
Wait, I thought early injected 911s used K-jet (aka CIS). :scratch: (corrected - ed)

More to the point, what's your take on the feasibility of using a 7-pin AFM with the 6-pin system, as I've advocated to Chris above? Am I leading the poor fellow on a wild goose chase?
I can't answer that. I do know that full throttle enrichment used to be external with the 6 pin, and internal with the 7 pin. This is beyond the mere addition of the TS I terminal.
Colin
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 93,996 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,113 miles

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SlowLane
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Re: What's up with this hole in the AFM flap?

Post by SlowLane » Fri Mar 27, 2015 12:33 pm

On my Vanagon system, the full-throttle enrichment switch is external to the AFM and is tacked on to the throttle plate actuation mechanism. There is nothing inside either of my 7-pin AFMs which suggest anything to do with full-throttle enrichment.

Of course, 1981 Vanagon /= 1975 Transporter, so the above may be as completely irrelevant as anything else that I've posted here. :blackeye:

Say Chris, would you be able to post some comparison pics of the innards of your 6-pin and 7-pin AFMs? That might help.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"Wisdom comes from experience. Experience is often a result of lack of wisdom."
- Terry Pratchett

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Amskeptic
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Re: What's up with this hole in the AFM flap?

Post by Amskeptic » Sat Mar 28, 2015 9:12 am

SlowLane wrote:On my Vanagon system, the full-throttle enrichment switch is external to the AFM and is tacked on to the throttle plate actuation mechanism. There is nothing inside either of my 7-pin AFMs which suggest anything to do with full-throttle enrichment.
The '75-early'77 had a throttle switch that provided its own loop for idle and full throttle.
Then it was integrated to within the AFM/ECU.

I don't think there is anything we can "see" inside of the AFM that would "show" us how VW engineered integral full-throttle enrichment. We could guess that the Vanagon microswitch actually shuts off the O2 loop which causes immediate enrichment . . . :cyclopsani:
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 93,996 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,113 miles

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SlowLane
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Re: What's up with this hole in the AFM flap?

Post by SlowLane » Sat Mar 28, 2015 10:27 am

Amskeptic wrote:The '75-early'77 had a throttle switch that provided its own loop for idle and full throttle.
Then it was integrated to within the AFM/ECU.

I don't think there is anything we can "see" inside of the AFM that would "show" us how VW engineered integral full-throttle enrichment. We could guess that the Vanagon microswitch actually shuts off the O2 loop which causes immediate enrichment . . . :cyclopsani:
Well, no O2 sensor on my Canadian/Federal-spec Vanagon, but the AFR does jump dramatically towards very rich when I mash the pedal to the floor to engage the switch in vain quest of perceptible acceleration. :joker:

Some old posts that I read on ShopTalkForums suggest that the AFMs with built-in FT enrichment may have a section of the wiper track at the full-flow end where the wiper lands on a bare metal pad instead of resistor material. Presumably that might be visible on inspection.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"Wisdom comes from experience. Experience is often a result of lack of wisdom."
- Terry Pratchett

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