I just installed my boost gauge. It has vaccum. The boost appears (up to 7psi), but there's no vaccum. I was wondering if there are other connections I have to do for it to work.

Here's how I've installed it: I Tied my wastegate line and my boost gauge connects on that.

Is there another hose/line I have to connect somewhere?

Thanks.

It's ok, I figured it all out.

Explain to us how you 'figured it out', if you don't mind. Please.

Yeah for sure.

As I said, I tied my boost gauge hose to the wastegate vaccum line. That way, the gauge couldn't read vaccum inside the intake manifold, because the trottle plate is always closed, so no vaccum.

I tied it to the bypass valve line and it works perfectly. It reads 12 Inch Hg (front mounted: is 12 good?).

Before I change that, the needle would stay at 4psi of boost because there was no vaccum to force the needle back.

12 is not good. Especially if you have stock cams. You have a big vacuum leak. I have 14in/hg with JWT C1 cams which are fairly big cams. You should have around 18-20in/hg on stock cams.

I'll check it out.

I checked all my connections and still have 12.

Is there a way to detect where is the leak? If I get somebody to control trottle and boost the engine for me, would I hear any pssshhh somewhere?

Is it possible that only one connection is responsible of my 6 lost Hg inches? Could it be before the turbo (from air filter to turbo)?

Thanks. I turned out that I need help anyway...

I just thougt about it:

My idle is at 1800 rpm or so ( I know I have to get it tuned!), could it be the cause of my low vaccum?

Thanks.

On my DET, at idle (800rpms) I get 16 in Hg vacuum. If you're idling higher than that, then you should be reading more vacuum, not less. Think about it - you're sucking more air in the higher the revs are. ;) Therefore more vacuum. For example I read 22 in Hg when I let off the throttle when cruising on the highway.

One way to check for leaks is to get some Carb Cleaner and spray it over suspecting tees and vacuum connections. Rev the motor well and look for bubbles. You can't boost the engine while in neutral, but the rev will zero the intake pressure and you might be able to spot bubbles.

If the vacuum leak is big enough, you will hear it leak (a hiss or pshhh) at idle.

What kind of boost gauge are you running?

I'm using a VDO boost gauge.

Someone just told me that the vaccum problem is between the block and the throttle plate. The intercooler piping has nothing to do with that.

So I'm just gonna check for the 1/4 air hoses for leak, not my 2" piping right?

Are you sure my idle doesn't influence it?

Originally posted by djisnx2000
Someone just told me that the vaccum problem is between the block and the throttle plate. The intercooler piping has nothing to do with that.

You mean somewhere in your intake manifold? I don't understand.


So I'm just gonna check for the 1/4 air hoses for leak, not my 2" piping right?

Are you sure my idle doesn't influence it?

You should be checking all hoses.

I remember when I was setting my car up that I teed the boost gauge into the wastegate line and it didn't read vacuum. The wastegate line was plumbed into the intake piping before the throttle body. However, now I have the wastegate line going back to a bung on the intake manifold. The gauge is teed off that line and reads vacuum and boost fine.

If you have your wastegate line fed into somewhere in your intake piping, it might not see "enough" vacuum for your boost gauge to read it. If so, just tee off your FPR for your boost gauge and keep close eye on those connections so they don't come loose or else BOOM! I highly recommend the use of zipties.

Good luck!

Ok I'll check this out tomorrow morning.

Here's how my vaccum lines are:

The wastegate line starts in the intake piping, near the BOV and goes to wastegate.

Another line starts from from the intake manifold and goes to the BOV. My boost gauge is connected to this line.

Your suggestion would be to connect the wastegate line on the BOV line and then connect my boost gauge on the wastegate line?

No. it is correct.

Yeah, you should be fine. Are you using nylon tees? Don't use brass fittings, they're not so good. Have you checked the connection to the back of your gauge?

Don't use brass fittings? Why not?

The brass fittings can work their way loose since their threaded. We all know how much the Autometer ones suck.

Nylon tees simply the teeing method and they are certainly robust.

wait a second.

you are idling at 1800 rpm? when cold, warm, or all the time?

if you are idling that high, your AAC valve may be open too much, that would cause a lower vacuum reading. check and adjust your idle, and make sure your TPS is properly set as well. then see what your vacuum reads.

also make sure you aren't using the vacuum port usually running to the EGR. the hole for it is on the throttlebody right on the edge of the throttle plate, so when the throttle is closed, it blocks the hole; also makes for really funky incorrect gauge readings with throttle movement.

andris