Vacuum / Boost Issue

[TSi96drvr]

I am sitting at about -20 vac or so at idle. Under High Rev it'll get to about -10 vac.

I just did a boost leak test and with the car off, 15 psi in the tester, reading 15 boost on gauge.

What am I missing?

UPDATE: Do I need to be under load for it to register properly? I have read that it can't simply be parked and get proper boost.

 

[wicketywacker96]

I am not an expert by any stretch but I will tell you that at idle, my car reads the same thing. Only while I am driving, will it change and show boost and so on. I thought I did something wrong until I took it out after installing my kit. Take it out and see if it changes.

 

[the_mork]

The car needs to be under load in order for the turbo to spool unless you have a very free flowing setup. On a mostly stock car you might see close to no vacuum but probably not any boost. Some cars can build a small amount of boost at the line and with an automatic you can build a lot by brake boosting.

 

[sirsol66]

Just as its been said, you usually can't built any (or a very small amount with tiny turbos like the t25, etc.) boost by free reving. Put some load on your engine and you should see boost pressure rise to whatever level its been set at. If you put a load on your motor and it still wont boost then you have other issues like massive boost leak, bad turbo, etc.

 

[TSi96drvr]

Thanks guy.

I would have taken it for a spin sooner, but I wanted to get a few things tested and out of the way (had it towed to my house when I bought it - risky, i know). Anyway, tests completed, I took it for a spin and now not only does it spool, but it goes way past the 15psi I thought I had the MBC set up for.

So the question I am pondering now is.. do I have a stuck wastegate or a bad / improperly configured MBC.

Time to search for the answer.

 

[the_mork]

I would be improperly set mbc. Start by backing it all the way out and then screw it in again just enough to to keep the screw in and then take it for a drive. Turn it in each time by 1/2 turn until it starts turning the boost up then only turn it up by 1/4 at a time until you reach your desired boost level.

 

[TSi96drvr]

thanks mork.

I was wayyy to far in there... I backed it all the way out.. and did a few tests with a vacuum pump and I think I am at least much closer..

 

[the_mork]

A vacuum pump would help you get close but IMO it isn't perfect because of the way that a lot of MBCs bleed air. The only way to test it for sure is to put the car on the road and run it starting from the bottom. When you take your car out be ready to let off fast the first time since you've turned it in some. It only takes about 10 minutes to dial in the MBC on the road so I wouldn't worry about getting it right while the car is still in the garage.

 

[TSi96drvr]

Yeah, I absolutely understand, but with no tags, no insurance and not even the car registered yet, I don't see myself going on the road much... especially where I live..

I need to really fix the backfire issue that I have first and then at least I can take it on the road without stalling or backfiring.. :\

Once I can get it on the road, I can't wait to have it tuned in.

Thanks.