avicenna110
SILVER Star
Hi everyone,
I thought this is worth sharing and having on here. Although for those who actually read the emission manual carefully (unlike myself) , the information was always there.
So I’ve read here about people testing their ABV, and concluding that it’s junk if it doesn’t hold vacuum. I have 5 of them, and none do, so I was pretty bummed out. (@pardion found 14 of his not operative here Wanted - 17670-61010 Air bypass valve 1/75 - 1/79 - https://forum.ih8mud.com/threads/17670-61010-air-bypass-valve-1-75-1-79.1297168/)
So like John (@pardion) in the above link I took one apart, thinking that the diaphragm was bad. My diaphragm was good, and in a very good shape actually. But I noticed a hole that is clearly part of the design. Moreover the shaft which the diaphragm is attached to is in the chamber where vacuum is supposed to be held, and from what I could see the shaft is not sealed (there is some play in it). I’m not sure if the area above the diaphragm is sealed or not either and what the function of the small hole is. I’d appreciate some insight if any one has. Here are some pics.
Seeing the above I was skeptical that the ABV was supposed to hold vacuum, and after searching for a while I found this forum:
1981 Chevy K10 4x4 smog pump diverter valve - Chevy Message Forum - Restoration and Repair Help - https://www.chevytalk.org/fusionbb/showtopic.php?tid/343171/
Which says there is a controlled leak engineered around the shaft for some early ABVs. Additionally due to this leak a hand vacuum pump is not strong enough to pull the diaphragm ( none of mine would close no matter how much I pumped). A sudden strong vacuum is needed. I tried it with a vacuum from a running car and sure enough all my 5 valves closed, but opened after a few seconds. Then I did what I should have done in the first place, read the manual carefully. It’s all written here:
It states the valve closes when you disconnect and reconnect, and air comes out the bottom temporarily, which confirms that the valve opens again. Disconnecting and connecting again closes the valve temporarily again. I think since the valve is only closed upon deceleration, you only want to stop the air injection temporarily. Also I think the VSV cuts off vacuum quickly so there won’t be a permanent vacuum leak.
Hope this is helpful and people don’t throw away their ABVs thinking they’re junk.
Bonus item, I found this Carter ABV that looks close enough to a Toyota, and functions the same. You can even put the top and bottom piece from a Toyota ABV to make it look stock.
I thought this is worth sharing and having on here. Although for those who actually read the emission manual carefully (unlike myself) , the information was always there.
So I’ve read here about people testing their ABV, and concluding that it’s junk if it doesn’t hold vacuum. I have 5 of them, and none do, so I was pretty bummed out. (@pardion found 14 of his not operative here Wanted - 17670-61010 Air bypass valve 1/75 - 1/79 - https://forum.ih8mud.com/threads/17670-61010-air-bypass-valve-1-75-1-79.1297168/)
So like John (@pardion) in the above link I took one apart, thinking that the diaphragm was bad. My diaphragm was good, and in a very good shape actually. But I noticed a hole that is clearly part of the design. Moreover the shaft which the diaphragm is attached to is in the chamber where vacuum is supposed to be held, and from what I could see the shaft is not sealed (there is some play in it). I’m not sure if the area above the diaphragm is sealed or not either and what the function of the small hole is. I’d appreciate some insight if any one has. Here are some pics.
Seeing the above I was skeptical that the ABV was supposed to hold vacuum, and after searching for a while I found this forum:
1981 Chevy K10 4x4 smog pump diverter valve - Chevy Message Forum - Restoration and Repair Help - https://www.chevytalk.org/fusionbb/showtopic.php?tid/343171/
Which says there is a controlled leak engineered around the shaft for some early ABVs. Additionally due to this leak a hand vacuum pump is not strong enough to pull the diaphragm ( none of mine would close no matter how much I pumped). A sudden strong vacuum is needed. I tried it with a vacuum from a running car and sure enough all my 5 valves closed, but opened after a few seconds. Then I did what I should have done in the first place, read the manual carefully. It’s all written here:
It states the valve closes when you disconnect and reconnect, and air comes out the bottom temporarily, which confirms that the valve opens again. Disconnecting and connecting again closes the valve temporarily again. I think since the valve is only closed upon deceleration, you only want to stop the air injection temporarily. Also I think the VSV cuts off vacuum quickly so there won’t be a permanent vacuum leak.
Hope this is helpful and people don’t throw away their ABVs thinking they’re junk.
Bonus item, I found this Carter ABV that looks close enough to a Toyota, and functions the same. You can even put the top and bottom piece from a Toyota ABV to make it look stock.
