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

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

Post by Amskeptic » Sun Mar 29, 2015 7:08 am

SlowLane wrote: 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.
It gets worse. Bentley claims you Canadians have series resistors like the older L-Jet buses, too. Do you?
The full throttle enrichment switch kills the O2 sensor and provides enrichment only when the speed sensor declares that the engine is over 3,000 rpm. We can make it more complicated if you like . . .

Never seen no bare metal pad. Those now-retired engineers at VW and Bosch would laugh at us monkeys here trying to figure out their coconuts.
"Hans, Hans, look at this . . . . can you believe it? Thousands of 'experts' opining away . . ."
"What? Where? HAHAHAHAHAHAHAHAHAHA"
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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

Post by SlowLane » Sun Mar 29, 2015 9:17 am

Amskeptic wrote:It gets worse. Bentley claims you Canadians have series resistors like the older L-Jet buses, too. Do you?
Sorry, "series resistors" is a bit ambiguous. If you mean the current-limiting resistors in series with the injectors being external to the ECU and mounted to the firewall in a little aluminium box, then yes, just like the Federal models.

And how is this worse? :scratch:
Amskeptic wrote:The full throttle enrichment switch kills the O2 sensor and provides enrichment only when the speed sensor declares that the engine is over 3,000 rpm. We can make it more complicated if you like . . .
This ain't fusion science. The 3000 RPM cutout is provided by the "OXS relay", which (on California models only) sits in series with the WOT switch and only closes the circuit when engine speed is over 3000 RPM. All the ECU sees is its full enrichment switch input closing. It neither knows nor cares if that closure is moderated by the OXS relay.
Amskeptic wrote:Never seen no bare metal pad.
I defer to your wider experience. After all, what is merely a hobby for me is a livelihood for you. But there has to be a difference in these that we could measure.
Those now-retired engineers at VW and Bosch would laugh at us monkeys here trying to figure out their coconuts.
"Hans, Hans, look at this . . . . can you believe it? Thousands of 'experts' opining away . . ."
"What? Where? HAHAHAHAHAHAHAHAHAHA"
I expect they would be astounded that anyone would even care to try and reverse engineer work they did 40 years ago. Well, any of them who are still alive and in possession of their faculties, anyways.

I think part of our challenge is in sorting out the incremental changes from year to year and region to region that blow up our carefully curated assumptions. Lessons learned from working on an '81 Vanagon don't necessarily carry over to a '75 bus, or even an '83 3/8 Vanagon (ie. just before the wasser). Just as lessons learned from working on type 1 engines and which are part of the widely treasured common lore don't automatically apply to the type 4 engine.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- 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 » Mon Mar 30, 2015 9:06 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.

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.
I didn't think to take a photo of it, but I believe that my throttle has the enrichment switch. I say this because there is a 5-pin connector on the housing.

As requested, here are pics of my collection of AFMs.

Image

From left to right:
*A 6-pin AFM used for parts. The air flap rubs within the housing. The wiper board was transplanted into the next AFM, (attached to the airbox).
Image
*This 6-pin AFM is the one that I'm currently using. It works well save for a nasty habit of the wiper arm getting stuck behind the fuel pump cut-off switch which prevents the car from starting from time to time.
Image
*The third from the left AFM is the new/used one. This is the one with the hole in the flap. I added the wiper arm ground wire and moved the board up a bit to give it new tracks.
Image
*Finally, aircooledchris' 7-pin.
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 » Mon Mar 30, 2015 3:16 pm

BellePlaine wrote: *A 6-pin AFM used for parts. The air flap rubs within the housing. The wiper board was transplanted into the next AFM, (attached to the airbox).
Image
I think with the socket from that parts AFM and a 7-pin harness connector with pig-tails you can easily cobble up an adapter harness to let you experiment with a 7-pin AFM and not have to modify your 6-pin harness at all. You would need to clip out or de-solder the diode (if it's in there) between pins 6 & 36 on the donor 6-pin socket and find a way to keep the fuel pump contacts on pins 36 & 37 from closing.

Can you see the part numbers of the resistor boards? Do they all say 1 288 310 021?

And oh, hey: can anyone read German? Here's an interesting post to a German Bulli forum that Google popped up: http://forum.bulli.org/forum/viewtopic.php?f=7&t=11880
The guy seems to not be too happy with the FIC AFM that he received, but maybe it's just that German looks like such an angry language to me.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- 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 » Mon Mar 30, 2015 8:19 pm

SlowLane wrote: Can you see the part numbers of the resistor boards? Do they all say 1 288 310 021?
Careful. Sometimes a part number precedes the finishing touches. People have shared casting numbers thinking that they were engine numbers. Some cylinder heads have the same part number with different size valves. If the resistor board has its own part number, it may have subsequent manufacturing variations.
NIR,
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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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 31, 2015 8:45 am

Amskeptic wrote:
SlowLane wrote: Can you see the part numbers of the resistor boards? Do they all say 1 288 310 021?
Careful. Sometimes a part number precedes the finishing touches. People have shared casting numbers thinking that they were engine numbers. Some cylinder heads have the same part number with different size valves. If the resistor board has its own part number, it may have subsequent manufacturing variations.
Okay, fair warning. But if the numbers match and he resistance profiles also match then I think we're on pretty good ground that the only differences in these AFMs must be the spring tension and the wiper position. Not to trivialize the task of getting those parameters in sync.

I've been mulling over how best to repeatably measure spring tension on these puppies. I have visions of Rube Goldberg contraptions involving pulleys and strings and weights and springs, oh my. The German fellow in the forum link I posted was using a linear tension meter of simple design, which would be a reasonable first cut, but not the most repeatable system.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- 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 » Tue Mar 31, 2015 4:37 pm

SlowLane wrote:if the numbers match and he resistance profiles also match then I think we're on pretty good ground

how best to repeatably measure spring tension on these puppies.
a) yes

b) SGKent on theSamba used a gram scale and an extension. PM him. I think 60 grams moves the wiper on a never fooled with spring.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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