VCV To Vacuum Modulator Pics

[curt5446]

Hi all,

PO had the vacuum routing all wrong. I have everything fixed with the exception of my 2-3 flair. It looks as if there are 2 ports on the VCV, one supplying vacumm from the vacuum pump and another running off to the vacuum modulator. Am I correct?

Can someone explain how the vacuum is SUPPOSED to be routed here?

I currently have the line directly off the vacuum pump teed above the VCV. One line going to the VCV through the vacuum damper and the other headed back to the vacuum modulator.

For reference, the line running to the modulator is holding vacuum like a champ.

Thanks in adavance,

Curt

[Brian Carlton]

Originally Posted by curt5446

Can someone explain how the vacuum is SUPPOSED to be routed here?

I currently have the line directly off the vacuum pump teed above the VCV. One line going to the VCV through the vacuum damper and the other headed back to the vacuum modulator.

For reference, the line running to the modulator is holding vacuum like a champ.

Thanks in adavance,

Curt

You have it correct.

The VCV is a bleed valve. It bleeds vaccum so that the modulator sees less than what is delivered by the vacuum pump.

Of course, to properly function, the VCV works in conjunction with a small orifice. The vacuum through the orifice is limited, thereby allowing the VCV to bleed small amounts of air and drop the vacuum level to the modulator depending on pedal position.

You can check the function of the VCV if you have a Mityvac. Connect the mityvac on the supply side (instead of the vacuum pump). Pump up the Mityvac as much as possible and read the gauge. It should be between 8" and 12". Now, with the Mityvac pumped up, slowly open the rack..........the gauge should fall slowly toward zero relatively linearly as the rack goes toward full open.

If the vacuum is too high, you'll get flaring and you'll need to make a tiny adjustment to the VCV to eliminate it.

If there is no modulation of the vacuum as the rack is opened, the VCV has failed and you need a replacement.

[curt5446]

Brian,

Checked vacuum feed side with my mighty vac and it held 15" Cycled the rack and no change so, I guess I found my problem.

Thanks a bunch!!

[Brian Carlton]

Originally Posted by curt5446

Brian,

Checked vacuum feed side with my mighty vac and it held 15" Cycled the rack and no change so, I guess I found my problem.

Thanks a bunch!!

Yes, with the rack fully open, you should not be able to get the Mityvac above about 1". If it pumps up and holds 15", the VCV is non functional.

BTW, 15" is way too high for vacuum at idle. I currently have the SD at 8" and it shifts perfectly.

[curt5446]

Let me clarify. I connected my mityvac to the input side of the vcv and pulled vacuum to 15". When I cycled the rack, it would not vent the vaccum. It held.
So I assume because the VCV did not vent, it is bad.
Sent from my EVO using Tapatalk 2

[Brian Carlton]

Originally Posted by curt5446

Let me clarify. I connected my mityvac to the input side of the vcv and pulled vacuum to 15". When I cycled the rack, it would not vent the vaccum. It held.
So I assume because the VCV did not vent, it is bad.
Sent from my EVO using Tapatalk 2

Yes, you are correct.