Another 355 Bypass Valve Thread!!

Gents,

I am pretty sure that the valve on my car does not work. Over the weekend, I wired it permanently open. Not only does that car feel sharper, it sounds like a proper 355.

Is there any risk of damage to the engine by doing this? I have done some searches, but cannot unearth any conclusive answers.

Thanks in advance,
Roger.

 

The 355 needs or likes some back presure in the sub3000 rpms range ,that is what the valve gives the motor ,I think you are ok runing the valve open ,,you just don't get the same preformance in the sub 3 to 4000 rpm range ,due to lack of the back presure from the open valve.
DAVID

 

This is what I broke today, I noticed the bypass valve has a threaded screw for adjustments. So I figure I would tighten it a little so the valve would be a little open all the time than fully open itself over 4K. First I broke the rod, but there was just enough thread left to still attach it. I have it about 1/4 open, which worked out well (if it holds, I only grab about 2 turns).
Than I had a friend rev the engine for me to 4-4.5K to check it. The valve doesn't open, it's not stuck, moves freely by hand. It seems to work off vacuum pressure, anyone know how to find a vacuum leak???

 

revving to 4500 may not do it unless you can run solid WOT enough to have no vacuum - the car can cruise at 4000 rpm and pull 15" of vacuum - notice that the car cruises quietly then growls noticeably when your foot goes to the floor? Was you freind just holding 4000 rpm or flooring throttle? A hard blip may be required to drop vacuum enough to actuate the valve.

 

This last post, the guy says his wife ran 5-6K and he watched it open and close, sounds like a lot of RPM's to rev in neuteral with no engine load. Is there another way to check it?
http://ferrarichat.com/forum/showthread.php?t=24595&highlight=bypass

 

I'd check it by using a Mityvac tool to manually operate the valve and then drive around with a vacuum gauge connected to the tube that connects to the valve and see what signals it gets under varying conditions. If both test OK, I'd think the valve has to operate correctly when connected.

 

I came up with a really good way to check if your bypass valve is functioning. I took a paper clip and snipped off the ends just leaving a "U" shape. Put it onto the very top of the rod that (suppose to) lift up when you accelerate. When you check it after a quick run down the street, it should be about half way down the rod. Now you can by hand move the rod up to see if where the paper clip is now, is the full range of motion in the rod. By the way mine is working perfect.-MICHAEL

 

Hi all;

at full load, i.e. at wide open throttle there is practically no vacuum to speak of, certainly not enough to open the bypass valve. Vacuum is created by the pressure difference either side of the throttle butterfly and the flow restriction in the intake system.

Because of this the 355 is fitted with a vacuum reservoir located in the right hand rear, behind the wheel (next to the secondary air pump). On my 355 the valve was not working and the cause was that the reservoir was leaking. It was poor quality -- no more than a tin can. I replaced mine with an aluminium container sourced from an army surplus store.

Anyhow, best way to verify the funtion is in two steps:

1. connect a vac tube to the valve spiggot and suck. If the diaphragm is OK then the valve will move. You will need a lot of sucking force to make the valve open fully. But this is not essential. Kink the pipe and check that the valve holds position for a few minutes. This test will show any slow leaks on the diaphragm.

2. 'T' a vacuum gauge into the vac circuit. Run the hose into the cabin through the window with the gauge visible and drive the car. If the Vac valve is opening (located below the reservoir) and the reservoir is OK you will get a reading at the right engine speed. Be sure to route the vac hose so it does not touch the exhaust system.

For info the valve opens at 2650 RPM in all gears except 3rd when the valve opens at 4000RPM.

Also, if you are thinking of changing the hose that joins the steel tube to the valve spiggot make sure to get silicon based rubber hose, NOT EPDM, PP or PVC. They will all melt.

Hope this helps,

Rob.

 

Rob the little paper clip trick I did worked great,not nearly as accurate as your but I don't have the proper equiptment for that, when I was testing for a leak, I blew smoke into the tube that connects the bypass valve. I would have expected the smoke to come out the intake for the vacuum pump but instead it came out the solenoid valve, do you think this is normal?-MICHAEL

 

Michael, that's normal & OK. When the EVR (electronic vac regulator) shuts it vents to atmosphere to let the bypass valve close. Rob.

btw, I like the paper clip idea. I might use it myself as a quick check.