Boost gauge at idle

[Ben_payne92]

Hey guys i just installed my boost gauge and when at idle its erratically moving between about 2 and -2 psi really fast, any ideas what would be causing this?

 

[Old.Tony]

Can't be the turbo, it should be hardly spinning at idle. Where did you connect the gauge to? Intake manifold? It might be reacting to the erratic movement of air in the manifold due to the cylinders drawing large amounts of air in. At idle, you probably have a butterfly valve nearly closed in the intake, and this will create a vacuum in the intake. It'll be particularly noticeable if you added it close to an intake port.

In the D40, the boost pressure is measured on the output side of the intercooler, which mostly removes all of the effect of intake valve open/close operations and EGR operations.

 

[Ben_payne92]

hey mate this is where i connected the gauge,

 

[Old.Tony]

In that case it might be reacting to the PCV. Here's something to try (not for long): disconnect the PCV from the intake and point it at the ground (not in your living room, it might leave an oil stain). Block off the connector that this hose came from so air can't get in. How's the boost gauge now?

 

[Horatius]

Which brand gauge?

I have fixed vibrating or noisy boost gauges in the past by dampening them. Fitting a piece of smaller diameter hose inside the hose to the gauge, usually near the gauge itself but at the t-piece would probably do. The last time I cut an inch or so off the pipe that you get with various spray cans which was a great fit.

 

[Wayno]

Can't be the turbo, it should be hardly spinning at idle. Where did you connect the gauge to? Intake manifold? It might be reacting to the erratic movement of air in the manifold due to the cylinders drawing large amounts of air in. At idle, you probably have a butterfly valve nearly closed in the intake, and this will create a vacuum in the intake. It'll be particularly noticeable if you added it close to an intake port.

In the D40, the boost pressure is measured on the output side of the intercooler, which mostly removes all of the effect of intake valve open/close operations and EGR operations.

Hey Tony, I am looking at also installing a boost gauge. My intercooler pipes are replaced with polished aluminium and the output side pipe has a small pipe coming off it and it's capped, is that where I can connect my boost gauge pipe to it looks the right size same as all the other vac pipes
Wayne

 

[Old.Tony]

Hey Tony, I am looking at also installing a boost gauge. My intercooler pipes are replaced with polished aluminium and the output side pipe has a small pipe coming off it and it's capped, is that where I can connect my boost gauge pipe to it looks the right size same as all the other vac pipes
Wayne

Sounds like a great place for it!

 

[Ben_payne92]

Which brand gauge?

I have fixed vibrating or noisy boost gauges in the past by dampening them. Fitting a piece of smaller diameter hose inside the hose to the gauge, usually near the gauge itself but at the t-piece would probably do. The last time I cut an inch or so off the pipe that you get with various spray cans which was a great fit.

Its SAAS mate, thanks ill give that a go and see how it goes

 

[tweak'e]

for gauge vibration check your T piece doesn't have a smaller internal diameter on one of the legs. that side goes to the gauge.
other brands will come with a disc shaped filter/dampener.
the vibration is actually caused the inlet valves opening and shutting causing a pulse to bounce back down the intake.

 

[Wayno]

Sounds like a great place for it!

Cheers