Bypass valve questions

[denglish318ti]

Hi, I am still trying to work out how this bypass valve works. At idle there is a vacuum in the throttle body and it lifts the valve open. At boost there would still be a vacuum in the throttle body and therefore it should stil stay open right?

I took the pipe off my bypass valve and plugged up the hose expecting the valve to be open all the time. To my surprise the car behaved exactly the same. At idle and no throttle it went to -18inmg, and when I floored it, it went up to 8psi. How would it still be working with no vacuum line going to it?

I know johnboy suggested connecting the bypass valve to the nipple on the manifold, might do that later.

I think my valve is making a swooshy sound, so I am trying to isolate the problem.


Here is my pic of the DASC setup, is this correct?

Cheers

[xxxJohnBoyxxx]

Originally Posted by denglish318ti

Hi, I am still trying to work out how this bypass valve works. At idle there is a vacuum in the throttle body and it lifts the valve open. At boost there would still be a vacuum in the throttle body and therefore it should stil stay open right?

I took the pipe off my bypass valve and plugged up the hose expecting the valve to be open all the time. To my surprise the car behaved exactly the same. At idle and no throttle it went to -18inmg, and when I floored it, it went up to 8psi. How would it still be working with no vacuum line going to it?

I know johnboy suggested connecting the bypass valve to the nipple on the manifold, might do that later.

I think my valve is making a swooshy sound, so I am trying to isolate the problem.


Here is my pic of the DASC setup, is this correct?

Cheers

Your setup correct, the bypass valve is closed unless it detects vacuum. No vacuum it's closed and in boost mode. If you leave it with no vacuum your SC is in boost mode at all times and will use much more gas...

[lpcapital]

Originally Posted by denglish318ti

At idle there is a vacuum in the throttle body and it lifts the valve open. At boost there would still be a vacuum in the throttle body and therefore it should stil stay open right?

No, that's where you get confused. At idle you have vacuum all the way to the TB, so the valve reamins open. When you are at WOT, you actually have atmospheric pressure all the way to the SC (because the throttle is open) and boost past the SC (because the bypass is closed and the manifold is sealed).

The bypass valve is normally closed and uses vacuum to open. That's why when you dinsconnect the line you still get 8PSI.

[denglish318ti]

Cheers for your replys, its starting to make more sense. One thing I still dont get though:

I disconnect the vacuum hose to the bypass valve, so it is shut all the time. I am driving at 5000rpm and am at 7psi boost at full throttle. I then let go of the accelerator and the boost drops to 18inMg whilst still at 5000rpm.

Surely with the bypass valve shut the boost should remain?

[xxxJohnBoyxxx]

Originally Posted by denglish318ti

Cheers for your replys, its starting to make more sense. One thing I still dont get though:

I disconnect the vacuum hose to the bypass valve, so it is shut all the time. I am driving at 5000rpm and am at 7psi boost at full throttle. I then let go of the accelerator and the boost drops to 18inMg whilst still at 5000rpm.

Surely with the bypass valve shut the boost should remain?

No how can you have boost when you took away all the air to the SC by closing the throrttle body. The supercharger is pulling for air but can't get any because the throttle body is closed so you have vacuum from the throttle body to the pistons. If it remained in boost the engine would run away to top RPM and never stop. All gas engines slow their rpm's down by starving the engine of air which creates a vacuum...Less air/gas = vacuum = less power less rpm. More air/gas = more power more rpm...add boost = additional air/gas = additional power over 0inMg

[denglish318ti]

Cheers John, that clears things up. Probably wasnt the bypass valve making a squeaky noise under accelleration as it was still doing it when the vacuum line was off.

Thanks. Dylan

[xxxJohnBoyxxx]

Originally Posted by denglish318ti

Cheers John, that clears things up. Probably wasnt the bypass valve making a squeaky noise under accelleration as it was still doing it when the vacuum line was off.

Thanks. Dylan

Check your idler pulley. The spring gets weak over time and the SC requires a god idler pulley bearing and spring to keep that belt from squeeking.

Also you will hear a squeak noise when letting off slowly as the throttle body closes it hits a point where the air whistles becasue the SC is pulling hard for air and your choking it off creating a vacuum by closing the TB. This is normal as sounds like a slight turbo spool sound

[denglish318ti]

Cheers for the tips, I will have a look tonight. The car has a really lumpy power curve up to 4000 rpm, and is accompanied by this whistling. I can feel it hold back as it whistles, and then its fine when the whislte stops

[xxxJohnBoyxxx]

Run the bypass vacuum line to the nipple on the DASC manifold so it gets boost to slam the bypass valve shut.

You got me stumped on this one. Is there a leak on the PCV valve hose that goes to the valve cover or is the PCV valve diaphram blown?

This is one of the main reasons I removed the RRFPR. It was very unstable during boost and I had power changes and misfiring which caused the bypass valve to open and close or flutter. I totally hated that regulator that's why I removed it and sold it. You can adjust it and go richer or leaner to try to get rid of that stumble...

Are you blowing a bunch of black exhaust when in boost? If so your way rich and need to reduce the regulator pressure. I had it turned up for a 3.4 pulley. Turn the adjustment screw on top counter clock-wise 1.5-2 full turns and give that a try but only if you blowing black rich exhaust.

Are your plugs all carbon fouled??

[denglish318ti]

Cheers for your reply John. I probably have the RRFPR set to run at too high a pressure then. Do you remember how many turns clockwise you turned it to adjust it when you put the different pulley on?

On a separate note, shouldnt you run the same RRFPR and rate of rise whatever pulley you are using? As if you get more boost the RRFPR will give more fuel pressure?

I thought it was the valve diagphram as when I sucked on it I could get it to squeak. But when I disconnected the hose to the valve (so that it was shut) I still got the squuuuuuuueak sound.

I dont know if I am blowing black smoke on boost, I am normally just trying to hold on, haha. I will have a look tonight, and check my plugs.

The RRFPR is totally rubbish, I wish I could get my ECU mapped, but living in UK I cant really send it to the USA, and I dont really trust random guys to map it in the UK.

Cheers for your help
Dylan

[xxxJohnBoyxxx]

Originally Posted by denglish318ti

Cheers for your reply John. I probably have the RRFPR set to run at too high a pressure then. Do you remember how many turns clockwise you turned it to adjust it when you put the different pulley on?

On a separate note, shouldnt you run the same RRFPR and rate of rise whatever pulley you are using? As if you get more boost the RRFPR will give more fuel pressure?

I thought it was the valve diagphram as when I sucked on it I could get it to squeak. But when I disconnected the hose to the valve (so that it was shut) I still got the squuuuuuuueak sound.

I dont know if I am blowing black smoke on boost, I am normally just trying to hold on, haha. I will have a look tonight, and check my plugs.

The RRFPR is totally rubbish, I wish I could get my ECU mapped, but living in UK I cant really send it to the USA, and I dont really trust random guys to map it in the UK.

Cheers for your help
Dylan

Yes you normally leave them alone. However mine was very lean so I turned it clockwise 2 turns. Turn it one turn counter clockwise and try. If it get's worst go the other way

[denglish318ti]

Cheers John, that may be the source of my bogging down.

[xxxJohnBoyxxx]

^^Most definately sorry about that. Should have told you when I sold it to you.

[denglish318ti]

No worries at all. I turned it 1 and a half turns anti clockwise, seems a bit better. Still has the bogging down at 2800rpm in all gears. I think it must be an airleak, as it still has that sweeeeeeeeak sound when at around 4psi boost. It wasn't the bypass valve as it still made the sound when it was pernamently shut. I plumbed it in so the boost keeps it shut though. I have reseated the manifold twice, so I don't think it's that. I am going to replace the injector o rings, as they were quite hard. Only other things I could think of was the seal from the manifold to the supercharger...

[lpcapital]

Once I installed the SC I was having a similar issue. In my case the problem was with spark plugs: the stock plugs were too hot. I switched to Bosch F6DSR. They are plugs specific for FI application: they have a silver plated core to trasnfer heat better, closer gap for better spark under high pressure and 1 heat range colder than stock. You can get the on Amazon. Check my thread here: http://www.318ti.org/forum/showthread.php?t=25697.