BicuspiD

Sorry for the long post. I tried to post this before and got no replies, I'm hoping perhaps with the additional info I can get some insight.

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) - on and off the car, and pressurized them. They are all fine. Swapped out BOVs, and tested the CRV - 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. The motor boosts fine, if a little sluggish to get there. Transition happens, and the boost drops to ~5, but quickly rebuilds (all the time hearing the venting sound) 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. Again 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.

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.

BicuspiD

anyone?

DaleClark

iTrader: (55)

Have you pressure tested your system yet? Get an air compressor, remove your intake and plug up the intake. Find a suitable nipple on the intake tract, and pressurize the intake to around 10-15psi.

If you have a boost leak, you'll hear it and feel it - move your hand around feeling for air leaking out. You'll be surprised what you'll find - I've found all KINDS of odd leaks like this. From pinholes in rubber vacuum caps, to a tiny pinhole in a weld for a BOV flange, to real major leaks.

It's also possible if you're smelling fuel a bit that you have a leak around the injector grommets. They might be sealing well enough at idle to not make a vacuum leak, but may be leaking out at boost. It's quite common for them to be shot.

Good luck!

Dale

jwhite94RX7

I think you're on the wrong track.

It sounds like you're saying you think that when you blip the throttle perhaps air comes OUT of the engine at the LIM gasket.

Usually if the LIM gasket is leaking, air would be going IN to the engine because at idle and even during the blip the engine would be under vacuum. It takes a pretty solid push and hold to redline of the throttle to build any boost in order to push air OUT of the LIM gasket. Even then it's usually only 3-4 lbs for half a second.

If your LIM gasket is leaking, there's also usually an idle problem. Typically the idle "hunts" going up and down at 500 - 800 rpm at a one cycle per second rate.

Checking the LIM gasket usually involves squirting carb cleaner around the LIM gasket to see if the idle hunting changes. To facilitate this I made a tool for directing the carb cleaner spray to the LIM gasket:

I got a thin coat hanger, wrapped then end of it around a large nail at 90 degrees to the coat hanger. I trimmed of the excess coat hanger leaving a pigtail at then end of about a foot and a half of coat hanger.

Then I inserted a small plastic tube through the pigtail and taped the tube along the coat hanger. This gave me a tube end at 90 degrees to the length of coat hanger.

I slipped the other end of the plastic tube over the tube that's inserted into the carb cleaner nozzle. I taped them together, but if the plastic tube is small enough that's not really necessary.

This tool allows you to position the end of the small plastic tube at various places on the LIM and spray carb cleaner there. When the carb cleaner fills the gasket leak, the idle hunting changes. Work bottom to top so that carb cleaner doesn't run down to places you haven't sprayed yet.

I hope that answers your question, but as I said above, I think you're on the wrong track with the LIM unless you're seeing idle hunting.

jwhite94RX7

A couple more thoughts:

I forgot to say that if you do have idle hunting due to a LIM gasket leak, removing the electrical connector at the air pump will affect the hunting.

Also, you can get a plastic tube about 3/8 to 1/2 inch in diameter and use it to listen for leaks. Just hold one end in your ear and probe the engine with the other end like a doctor with a stethoscope.

DaleClark

iTrader: (55)

Good input there. I prefer using starting fluid for finding vacuum leaks - it dries very quickly and doesn't leave a potentially flammable residue behind.

I have seen cases where there was a boost leak and not a vacuum leak - the material that had failed (paper gasket, rubber coupler, whatever) would let air out, but would seal up when a vacuum was applied. Makes it very tricky to find the leak!

Also, most FD's I've seen with bad lower intake manifold gaskets had *high* idles - 1200-1500 RPM, and really rough. But, there are different levels of bad gaskets - some are more blown than others.

Good trick on making a leak detector, BTW!

Dale

BicuspiD

Thanks for the responses. perhaps I didnt post as clearly as I was thinking...


I was describing the wind/air from behind the UIM when the air pump is connected to see if this might signify a breach, and maybe make the fuel smell coming from the cats, through the (I think) split air pipe? I don't think the air pump is physically able to flow the amount of air I am hearing though.

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

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

jwhite94RX7

In your first post you said "behind the LIM".

So you don't really know you have a boost leak.
You just have a loud leak sound and an unexplained air flow behind the LIM, right?

Sounds can be deceiving. Loudness is not always indicative of large flow.
As for the air flow, try the "tube in your ear" trick I mentioned. You should be able to feel the air flow in your ear when the tube is pointed toward the source.

Good luck !

BicuspiD

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 ) 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 yeee HAW

Thanks for getting me off the LIM track Jwhite94RX7. If you are going to sevenstock tomorrow, I'll buy you a beer afterwards!

jwhite94RX7

Congratulations!