Decel Valves ....

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tommu
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Decel Valves ....

Post by tommu » Thu Aug 01, 2019 3:48 pm

Amskeptic wrote:Decel valves (vacuum limiting valve) simply add air when you snap the throttle shut. This prevents the prior charge of fuel that was introduced before you changed your mind from having to burn with little to no air.

VW utilized a solenoid-controlled decel valve on the automatic transmission buses to keep the idle from dropping too dramatically when you selected a gear. Tommu wants to press one of those into service to perform the same task when he turns on his air-conditioner. The same power that energized the A/C clutch can also open the decel valve.
Colin

SlowLane wrote:
Thu Aug 01, 2019 9:02 am
Check the operation of your deceleration valve with the Mity-Vac. On a CA-emission vehicle it should open at 15-17" Hg.
Could you expand upon this please?

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SlowLane
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Re: AFM Adjustment

Post by SlowLane » Thu Aug 01, 2019 5:10 pm

tommu wrote:
Thu Aug 01, 2019 3:48 pm
SlowLane wrote:
Thu Aug 01, 2019 9:02 am
Check the operation of your deceleration valve with the Mity-Vac. On a CA-emission vehicle it should open at 15-17" Hg.
Could you expand upon this please?
Based purely on measurements I took on a (ie. sample size of one) CA-spec decel valve vs. a Federal spec decel valve with my Mity-Vac. The CA-spec valve opened at about 15-17" Hg, while the Federal-spec valve opened at ~22" Hg.

Since CA-spec vans have a lower idle vacuum (~12" Hg) because of their late idle timing (5 degrees ATDC) this normally shouldn't pose a problem. But if one were to unwittingly mount a CA-spec decel valve on an engine tuned per Federal specs (7.5 degrees BTDC), then one might see some unusual behaviors with the decel valve opening just from the normal idle vacuum of ~17" Hg on such an 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."
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asiab3
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Re: AFM Adjustment

Post by asiab3 » Thu Aug 01, 2019 7:12 pm

Do you have part numbers for the differences? I never knew there were multiple.
Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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SlowLane
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Re: AFM Adjustment

Post by SlowLane » Fri Aug 02, 2019 6:00 am

asiab3 wrote:
Thu Aug 01, 2019 7:12 pm
Do you have part numbers for the differences? I never knew there were multiple.
Robbie
Yes, but I'll need to dig through my parts stash to find the two articles. That will have to wait until the weekend.

IIRC, there are differences in the mounting brackets as well. I believe the CA valve has a shorter bracket.
'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: AFM Adjustment

Post by Amskeptic » Fri Aug 02, 2019 5:38 pm

SlowLane wrote:
Fri Aug 02, 2019 6:00 am
asiab3 wrote:
Thu Aug 01, 2019 7:12 pm
Do you have part numbers for the differences? I never knew there were multiple.
Robbie
Yes, but I'll need to dig through my parts stash to find the two articles. That will have to wait until the weekend.

IIRC, there are differences in the mounting brackets as well. I believe the CA valve has a shorter bracket.

There is our garden variety huge vacuum canister decel valve on all fuel injected buses.
0 280 160 303

There is a little weird looking decel valve for automatics with an electrical plug to open additional air when you select "Drive" in the 1975 003 transmission, and I think they got rid of the electrical switch in 1976 with the 010, but they share this sort of fuel pressure regulator look:
022 133 551 C

There is a high altitude decel valve which is designed to require lower vacuum signal to open sooner because it is already rich up there at high elevations.
0 280 162 102


One more decel valve for CA 1979.
0 280 160 313

The 1975 FI bus had 5* ATDC retarded timing too, and with an automatic, it needed a blast of air if you selected a gear from neutral.
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: AFM Adjustment

Post by SlowLane » Sun Aug 04, 2019 7:06 am

Air-cooled CA-spec Vanagon decel valve in my possession has these part numbers:
Bosch: 0 280 160 319
VW: 071 133 551A

I also confirmed my recollection that this valve begins to open at 15" Hg, and is fully open at 17" Hg.

I'm afraid that I didn't make a note of whether the junked Vanagon I pulled it from was a manual or automatic.
'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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tommu
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Re: AFM Adjustment

Post by tommu » Mon Aug 05, 2019 1:45 pm

Now I'm looking for an automatic Decel valve with the selector-activated air bypass. Would this be an option?
https://www.thesamba.com/vw/classifieds ... id=1758588
Image
p/n 311 906 171 but very similar to the one on the right here:
Image
The one on the left (022 133 551C) is a vacuum 761/2 -79 auto decel valve and the one on the right (022 906 047A) is a 75-761/2 auto electric decel valve.

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Amskeptic
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Decel Valves ....

Post by Amskeptic » Tue Aug 06, 2019 7:15 pm

Decel valves (vacuum limiting valve) simply add air when you snap the throttle shut. This prevents the prior charge of fuel that was introduced before you changed your mind from having to burn with little to no air.

VW utilized a solenoid-controlled decel valve on the automatic transmission buses to keep the idle from dropping too dramatically when you selected a gear. Tommu wants to press one of those into service to perform the same task when he turns on his air-conditioner. The same power that energized the A/C clutch can also open the decel valve.
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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