I have been tearing my hair out (both of them!) to find my boost leak.



I have checked all couplers (IC hoses and the Y-pipe coupler + 1 inch hoses) - on and off the car, and pressurized them. They are all fine. Swapped out BOVs, and tested the CRV (vacuum open/ - atmosphere/pressure closed)- all within spec. Vacuum lines, fuel lines, FPD, injectors cleaned, everything under the LIM redone about 6 months ago, and was working perfectly.



When I get on the throttle, I hear a loud audible boost leak. noticeable from 0 vacuum all the way up through to 10psi. The motor boosts fine, and transition happens, all the time hearing the Whoosh! venting sound, and builds up to 10 psi, then drops off (as is normal for my car - I think cat is clogged) but the leak is definitely there. When I get off throttle after a high-boost run, I can smell a slight fuel smell which does not exist at idle/low load. The car responds good, the gauge shows "normal" boost. But the leak is very loud, louder than the intake/exhaust noise! Sounds like I'm losing a ton of air somewhere.



When the car is idling, if I put my hand behind the LIM and blip the throttle slightly I can feel air moving from somewhere. If I disconnect the electrical connector at the air pump, this "mystery wind" seems to stop under the same test. I thought it was a leaking ACV but most people have told me a boost leak from the ACV is very unlikely. So I am leaning towards the LIM gasket - I am running out of places it could leak this much air from. I was guessing a turbo housing bolt might have backed out, and the compressor housing "separated" making the noise and leaking boost out the side, but that wouldn't explain the fuel odor.



Is there a way to test the LIM? If it has to be redone I'm gonna have to rethink my entire buildup plan, as this will be a lot of labor and I can do other things at the same time. I have a 99+ y-pipe on order to alleviate any concerns of the black plastic crossover pipe, but in testing it was fine.



Any suggestions you guys can give would be wonderful. I mean, theres only so many places you can lose air from that make such a loud noise. I am running out of places to check, and they keep getting to be more and more expensive to find/fix s I eliminate the low priced stuff

Sounds like a stud to either the turbo or exhaust manifolds. I bet John could diagnose it just listening to it in 30 sec and not charge you cause he's too busy to fix it "lol". Check to see if the nuts came off, came loose or the studs backed off or are missing or go to Mazdatrix.

i have the same exact symptoms on my car..... and i found the leak to be underneath the crossover pipe, it wasnt a small hole either, it is big enough to fit a finger or two

Seriously the best way to fix these types of problems is to remove everything all the way down to the turbos, inspect it all closely and then reassmble it all back using siicone couplers and "T" bolt clamps.

9times out of 10 it is something really simple like a shitty coupler od a clamp that wasn't seating properly. But unless you pull it all off finding the problem can be a real bear. And yes if you havent already replaced the original gasket between the UIM and the LIM with the updated metal one then that is a good possibility of harboring a leak as well.

Thanks for the responses



Supposedly when the motor was rebuilt (~20k miles ago) they used a new style LIM gasket. I dont think the old ones have been in production for the last 5 or so years, so I tend to agree, and dont think the LIM gasket is bad, just running out of places to check. If you heard the sound of boost escaping that I do, you'd expect to find the IC pipe disconnected!



The fact that I am reading 10+psi of boost on the gauge (plumbed to the nipple on the UIM) and the (relatively good) performance of the car boggles me. it also leads me to believe my turbos are working overtime and I'm beating the crap out of them.



I have removed, folded, inspected, and pressure tested all the couplers and IC hoses and they are solid. I have a 99 spec Y-pipe on order and am making some intercooler piping, so then it won't be an issue. I know its not going to solve anything though, other than future failure. I'll keep plugging away. I probably should wait until Monday to do this so I can bring my car to 7stock.....but I won't https://www.nopistons.com/forums/pub...DIR#>/wink.png



Thanks again for your input and Ill keep ya posted as to what I find

hmmm..... have you checked your intercooler?

Problem Solved!



The forwardmost nipple on the front half of the Y-pipe was broken off!



This caused the loud boost leak noise, explains how I could maintain boost with the leak, and also explains the fuel smell! The other end of the hose goes to somewhere on the LIM, under the injectors.



So I figure it was like this - I would boost... the vac leak was small enough that the turbos could maintain proper boost levels (but were sluggish), although large enough to make that godawful noise. Since it wasnt connected to the Y-pipe, the end of the hose from the LIM was spewing fueled charge air.(this is the only part I am assuming, but since the smell went away with the repair, its reasonable to assume. I still don't know where/what exactly this vacuum line should do, but its connected now https://www.nopistons.com/forums/pub...IR) More noticeable after a hard run was the smell, which also makes sense, as the residual excess fuel/air in the manifold from boosting was to be rerouted into the intake, only to escape to atmosphere.



I installed the Efini Y-pipe and a new O2 sensor, (plus changed out the BOV hose since mine was pretty bad), and viola! Boosts 11-8-12 and then drops off due to my clogged cat. yeee HAW



thanks for the suggestions guys, I figured I'd post the end results so if this comes up in a search, its complete for the searcher https://www.nopistons.com/forums/pub...IR#>/smile.png

Not sure which nipple this is? Perhaps you're referring to the charge control actuator chamber "A" nipple. This is supposed to get vacuum from the vacuum chamber. Vacuum applied to this actuator keeps the CCA butterfly plate closed from 0 to 4500 rpm, sealing off the primary boost from the secondary boost.

I can't seem to export the pic from the /pdf file, but if anyone has the service manual, in the fuel and emissions section, F-7 is a diagram of the entire system outline. The nipple that broke off I am referring to is labeled A with a circle around it.. you will see that it attaches to the other A which is on the LIM under the injectors..



i cannot find another reference of this nipple/connection in the service manual.



It is apparent on the vacuum diagram as the lowest pressure hose on the lower left - from Y-pipe to LIM - but what exactly is its function?



http://www.scuderiaciriani.com/rx7/v...ressurized.gif