vac = 10 at idle, can't boost past 5 psi

[kc92awd]

Like the title says, My vac is reading 10-11 at idle. I can't build more than 5psi boost. Car is running very poorly.

I pulled the hose to the wastegate. That didn't help.

The compressor spins freely, no shaft play.

I pressure tested the intake. There is a leak in the throttle body seals. But, I didn't have a problem holding 20psi for a while. I don't think this is keeping my boost at 5 psi.

I found another thread where the timing belt slipping one tooth caused a vac of 10, but it didn't say anything about that affecting boost levels.

Thoughts?

 

[ImportModder]

good vacuum is about 20, so if you have a healthy engine, it should be near that. When the timing belt jumps a tooth, the valves aren't where they are supposed to be at. Meaning, a intake valve would be open at the same time as an exhaust valve. Well, then there goes your boost. Check to see if your cams and crank all line up. If your car did jump timing, it would run poorly.

 

[oldman]

I question the fact that you're able to hold 20psi for a while with a shft seal leak, I find that hard to believe with my experience with boost leak tests. In any case, I would definitely check the timing marks. Are you still on stock cams?

 

[kc92awd]

Okay, the two problems were unrelated. The wastegate actuator arm slipped off the wastegate. The cotter pin was missing. Boost is back to normal.

Vac is still at 10. I'm believe this is because of the throttle body seal leak.

 

[importboost]

a boost leak will def make your vac not read correctly. but if you did your boost leak test right you would know that your seal was bad.

 

[kc92awd]

a boost leak will def make your vac not read correctly. but if you did your boost leak test right you would know that your seal was bad.

?????
I do know my seal is bad. Read again.

There is a leak in the throttle body seals. But, I didn't have a problem holding 20psi for a while. I don't think this is keeping my boost at 5 psi.

Vac is still at 10. I'm believe this is because of the throttle body seal leak.

 

[importboost]

but my ? is how did you hold 20psi with leaking seals...shouldnt be possible

 

[kc92awd]

but my ? is how did you hold 20psi with leaking seals...shouldnt be possible

I wasn't saying I held 20psi for 30 seconds. I was saying I could easily pump 20 psi with the compressor and air didn't rush out quickly.

It hissed slowly out of the throttle body and remained above 5 psi long enough to make it obvious that a boost leak wasn't keeping the turbo from pushing more than 5 psi.

This proved to be accurate as I can hold 15 psi with no problem now that the wastegate is hooked up properly, but the throttle body seal leak remains. I think it would have to be a huge and obvious boost leak to keep max pressure at 5 psi. That's why I believed I had some other issue, such as a timing belt problem.

I'm sure that the seals going bad is a slow process and they leak at varying degrees. Perhaps you have seen some very bad ones that seriously hindered the intake piping from holding pressure. Mine are apparently not that severe yet. But I do think they are bad enough to screw up my vac at idle.

 

[importboost]

ah i understand now. thanks for the clarification. yeah fix those seals. will def run better. also double and triple check that timing just to make sure.