[Carlos45]

Inspired by some posts on here, I've fitted a boost gauge to my car (2000 S-Turbo) today. It's showing no boost at all. :icon_confused:

There's a momentary vacuum when changing up a gear during acceleration but that's it. The gauge was tested before fitting and responded to boost and vacuum OK.

The car seems to accelerate OK, smoothly but not exactly 'push you back in your seat'.

I took the intercooler off when fitting the pipework for the gauge and there aren't any visible splits in the Y piece. I've also cleaned out the bypass valve, throttle body, restrictor pill and boost solenoid. There's a very small amount of movement in the solenoid, about 1-2mm or so.

Any ideas/suggestions as to why it's showing a boost of zero bar appreciated...

 

[StealthTL]

What line are you reading for boost?

I think the BPV line is the one to tap.....

S

 

[Carlos45]

I think I'm using the correct line...

It's a two port bypass valve. The connecting pipe from the chamber nearest the intercooler has been blanked off (so that chamber just vents to the inlet manifold) and the boost gauge is fed from the now-spare tee in the pipe from the chamber furthest from the intercooler (the one which goes to the boost solenoid via the restrictor).

Hope that makes sense!

 

[StealthTL]

Follow 'em back, you need a direct connection to the intake manifold....

Sounds like you are connected to the turbo lines - you need to be tapped into the Bypass valve line, the valve on the intercooler outlet.

 

[don1952]

I think I'm using the correct line...

It's a two port bypass valve. The connecting pipe from the chamber nearest the intercooler has been blanked off (so that chamber just vents to the inlet manifold) and the boost gauge is fed from the now-spare tee in the pipe from the chamber furthest from the intercooler (the one which goes to the boost solenoid via the restrictor).

Hope that makes sense!

A photo of the setup would be VERY useful.
I think I know what you are saying but its not clear.

 

[Carlos45]

Sorted! :Banane17:

It was connected to the turbo lines - I connected it to the intake manifold line instead and presto, it's showing vacuum at idle then boost under acceleration. Now to find a nice straight, quiet bit of road... :icon_biggrin:

Thanks to all who posted.

 

[Carlos45]

I've worked out why I initially connected it to the wrong line - somebody had previously connected the bypass valve ports the wrong way round. :icon_confused:

Swapped the pipes round this evening and it's a different car - previously the boost gauge hovered around 0.2 bar but now it boosts straight up to 0.5 (that's just from nipping round town). The car is also much quicker and smoother, not surprisingly!

There's a photo of the current setup at i184.photobucket.com/albums/x159/carlbowman45/Bypass_valve.jpg (can't do a direct link here) - if someone could confirm that it's correct I'd be grateful. Also, is the previous incorrect plumbing likely to have done any damage?

 

[don1952]

The valve to inlet manifold with tee for boost gauge looks OK, however where you have the "boost line" connected should be teed to the existing manifold line where you have taken the tee for the boost gauge. Pipework marked 22310 on attached

What you have labeled as the restrictor pill is just a pipe joiner, usually for two different size pipes.

 

[Carlos45]

The valve to inlet manifold with tee for boost gauge looks OK, however where you have the "boost line" connected should be teed to the existing manifold line where you have taken the tee for the boost gauge. Pipework marked 22310 on attached

I've removed link 22310 so the pipe I've labelled (perhaps ambiguously) 'To boost line' now goes directly to tee 22314 (as per the bypass valve mod posted elsewhere on here) - should the link be reinstated?

What you have labeled as the restrictor pill is just a pipe joiner, usually for two different size pipes.

Sorry, should have been more clear, the restrictor pill is in the smaller pipe connected to the reducer (hidden underneath the HT lead boots).

 

[Bassmaker]

HI Don. I've looked at the photo showing the way Carlos attached his boost gauge but I have mine done differently, my gauge is t'eed into the line from the manifold to the boost controller. When my car is idling there is no movement of the needle indicating vacuum but the boost "seems" to be okay. I am using an MBC set to 0.75 bar (99MY with a TD04L recently added) but under hard acceleration in 3rd and 4th I sometimes get fuel cutoff and am wondering now that I have seen Carlos's work, if I have the gauge attached in such a way as it's inaccurate? I've uploaded a photo of my work and wonder if you would cast your experienced eye over it please. Thanks. Tony.

 

[StealthTL]

Hey Tony
You didn't ask me, but I'll give my input anyway - the only thing you are measuring at that point is the turbo output pressure.

You'll get no indication of what the psi is after the intercooler and no idea what the actual manifold boost pressure is. You won't see any vacuum, nor the transition from negative to positive manifold pressure.

It's useful to know what the turbo is outputting, but since a lot of it just recycles back through the bypass valve, it's fairly academic.....


S

 

[don1952]

AFAIK.........
Doing the Bypass valve mod entails disconnecting the pipe nearest the intercooler, leaving that connection on the Bypass valve open to atmosphere and then plugging the open end of the pipe. This allows the bypass valve to act similar to the impreza version.

If you re-install your pipework to original you can then use the disconnected pipe that would have been plugged to connect your boost gauge.

 

[Carlos45]

My understanding of the bypass mod is that its main purpose is to remove the link between the two chambers of the bypass valve and that instead of venting to atmosphere, the (metered) airflow should remain in the system.

I'm quite happy to be corrected though!

 

[don1952]

My understanding of the bypass mod is that its main purpose is to remove the link between the two chambers of the bypass valve and that instead of venting to atmosphere, the (metered) airflow should remain in the system.
I'm quite happy to be corrected though!

You are referring to the fitting of a "Vent to Atmosphere" BOV, whereby the main recirc line is plugged and large connection on the Bypass valve remains open.

The effect of leaving the "small" connection nearest the intercooler open and plugging its pipework means that the valve is less progressive and less likely to leak. There is no "metered" air flow in either of the two smaller pipes, they just control the setting at which the bypass valve opens and is basically manifold pressure.

 

[The Rookie]

Ok I'll correct you...

The lower valve chamber acts to soften the valves action, its fed with manifold pressure that (due to the bleed back to the (pre turbo) intake) is closer to atmospheric than the pressure (vacuum or boost) in the top chamber.

On old valves with the spring going soft that extra boost fed to the 'wrong side' of the diaphragm opens the valve and boost is leaked away back to the intake, the turbo cannot overcome the leakage and give full boost, remove the pressure feed to the lower chamber so it only sees atmoshperic (as it does on the Impreza valve) and it shuts and hold boost.

Simon

 

[Bassmaker]

Hey Tony
You didn't ask me, but I'll give my input anyway - the only thing you are measuring at that point is the turbo output pressure.

You'll get no indication of what the psi is after the intercooler and no idea what the actual manifold boost pressure is. You won't see any vacuum, nor the transition from negative to positive manifold pressure.

It's useful to know what the turbo is outputting, but since a lot of it just recycles back through the bypass valve, it's fairly academic.....


S

Thankyou S. I always seek out Simon and Don for expertise and it's great to find another head. The explanation you give makes sense although I couldn't have seen it without your input, ta. I seem to be forever leaning on Simon for info which is a bit embarrassing for me. Thanks Don for the simple attachment of the gauge which is handy as I have already done the recirc valve mod courtesy of Simon.

 

[Bassmaker]

Thanks for all the input. I have re-done my plumbing but just to make sure, would you look at the 2 pics I have attached please. In the picture of the whole engine (1010934) I have marked the pipe at 7 o clock as "blanked off", it originally went to the upper outlet of the recirc valve and somewhere else too. I have taken the feed for the boost gauge as suggested by Don and S and even though I have chosen a long way around to the bulkhead (it's the black tube supported by the white cable ties round the back of the IC), would that be an issue? I figured there would be less heat that way but if I should have gone in a straight line, please let me know.

Thanks to all. Tony

 

[Carlos45]

Thanks for the info chaps. It's been an educational week!

Had to do a trip up Leeds ring road today (mostly dual carriageway with lots of traffic lights/roundabouts etc.) and the difference is amazing. Which set me wondering: with the bypass valve connected the wrong way round, would this setup be keeping the valve open when it should be closed? That would explain the previous less than earth shattering performance and its turbo nutter transformation. :icon_biggrin:

I've disconnected the pipework as per your diagram Don - Subaru have thoughtfully made this dead easy so it was a simple job of removing the tee and a short stub of larger pipe then reconnecting what was left (I'll try to post up a couple more pics later).