Hey guys,
I'm chasing down a boost leak after replacing an injector so trying to find the culprit. I was hitting 1.4 bar before but now only hitting .9 bar. I have replaced the intercooler piping (and f hose )and also had to pull the large air plenum to replace the injector so that's where I am looking.

I took the air plenum out again tonight after not being able to see any visible leaks after pressure testing from the lower boost hoses prior. When I did pressure test, all ic pipes were fine but I heard some noise from the middle of the engine (throttle body area). Since I wasn't in there before the low boost I figure I should start where I already was, as I doubt it randomly started the same time I was messing with the injector.

There appears to be a white check valve under the diverter valves, with a black line then a clear line coming out of it. Upon further inspection that line is running nowhere. I wasn't sure if it was supposed to vent to atmosphere or possibly run over to plenum behind throttle body.

A. Where should this go?
B. Could a small vacuum leak like Thai cause a reduction in boost from 1.4bar to .9?

Thanks for anyone who can chime in and help!!

 

isn't it item 21 on this picture, in fact a check valve…. It goes to a T and the top portion of the diverter valves….

 

This distribution block has a line coming out of the right side that bends up and ts into the diverter valves... Is that correct? You can also see that check valve under the f hose in the top left of this picture.

 

When I rebuild the top of the engine I used these …You should be able to figure out where they go with these drawing….

 

so looks like it runs over to the plenum, does that look accurate?

 

Sorry I don't have access to my car tonight and I don't remember having a vacuum line going over the plenum. I do remember a line going under the plenum to the n75 valve (parts cat item #44) with is besides the fuel cooler, line 42 on the parts cat picture.

 

And item 45 (change over valve) attach to the check valve you mention, got a line #27 that goes to a T on top of the diverter valve...

 

hissing noise from the tb/plenum area is probably the check valve and boost will be lost like a vac leak. they simply get old and crack.

 

the check valve that i posted a picture of, or a different one? Got a p/n or a schematic?

 

i dont i'm sorry. the check valve in the schematic #22 that jp posted is most likely the culprit. it IS the one closest to the plenum ( iirc ) and there are two. they are so inexpensive i would replace them both and the n75 also same time. it eliminates them as the cause which they are likely to be. particularly if you heard any escaping air when pressure testing from the turbo inlet.

worked for me. two check valves and the n75.

 

What information are you looking for? My car is currently torn apart and I just checked/replaced both of those black/white check valves (one of them had failed). I can grab some pictures or explain the routing if you need.

#21 listed in post 2 is the correct part number (there are 2 #21 check valves). One end, the black end, of the check valve you posted goes to part #45, the change over valves (controls the bypass valves). The white end of the check valve leads to the plenum(post throttle body) via a white, hard plastic line.

The ends of the hard plastic lines can sometimes pull out of their rubber connectors. I zip-tied all rubber connectors so they hold the hard plastic lines better.

 

one of those posted pics has it listed as 21 the other as 22 but that may in fact be a line. i also believe the #21 that jp outlined in RED is correct.
all you need to know is there are ( two ) and they should both be replaced if in doubt. n75 is insurance since it is the boost recirc valve!

 

Found it!! On the plenum behind the throttle body!! Time to put it back together and test again.

 

Easy fix! While you're in there, zip-tie all the other connections. Even if they aren't falling out they can still be loose and leak air.

 

thats the one way for the dvs.. in goes to the left side of the plenum....