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Discussion Starter · #1 ·
Hi all, I'm trying to find a boost leak I'm pretty sure I have in my Gen2. I've got the tester attached just after the AFM. I tried to pinch off the PCV hose to the valve cover with a Vise-Grip, but wasn't able to get it completely closed off that way, so I disconnected it and plugged it. I've read comments on here saying I also need to close off the air hose from the idle air control valve, which I've tried to do, but I'm not certain I have the right hose. I think it connects underneath the throttle body on the left side, and runs under a pair of water hoses. Anyone know if I'm on the right track here?

So I can only get the gauge on the tester up to about 3psi. I hear a hissing sound that as best I can tell is coming from the bottom of the throttle body. I don't think it's in the short hose between the cold pipe and the throttle body; I removed and inspected that, and it seems okay. I think I might have a bad gasket on the throttle body, but I can't feel any air coming out, nor is the soapy water any help -- can't see down there. I guess my next step is to remove the throttle body.

Anyone have any other hints? The smoke trick seems like a good idea, but I don't have any handy way to generate any, or to get it in there.
 

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I’d be removing IACV and rebuilding it as it’s a common fail point. Clean it up and bench test TPS as well as Idle Control. Beware of coolant lines leaking so best to pinch these off first.

Jimb
 

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I get all tree huggy ... I used an incense stick . If you do that at dusk then shine a bright light in it , it works really well .

Sent from my LM-Q910 using Tapatalk
 

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The TVIS seals always gave me trouble with boost leaks. Here is how to replace them or you can delete the TVIS completely and get a phenolic spacer.


 

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I tried boost leak testers as well as the smoke method, and I like the smoke method. It is not pressurized (though you can make/buy one that does pressurize close to boost pressure), but it does give a great visual on leaks that I didn't see with compressed air and soapy water. There are some youtube videos on how to 'build' your own or you can order something simple from Amazon.

In terms of setting the test up with compressing air - it sounds like you have it set up right if you are right after the AFM and the line from the IACV that goes back to the intake is distal to where you have your tester hooked up (i.e. it is all contained within the circuit). The line from the IACV joins up to the metal lines that then go back to the intake piping (I think one is AC idle up and the other is the IACV, but I can't recall exactly off hand). When testing AFTER these lines recirculate (i.e. they are out of the circuit and will leak air) I just cap it at the metal line with an appropriately sized heater hose rubber cap.

There was a post recently where someone set up their tester with a simple pump via a brake booster line and plugged the intake (so bypass the turbo and IC circuit totally) which was sorta cool.
 

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Discussion Starter · #7 ·
Thanks for all the replies. I don't normally do my own engine work, but I decided to give this a try because it sounded like it might not be too hard, at least to find the leak if not to fix it. I certainly don't have my own machine shop -- I had to look up the meaning of "swage" :)

So I haven't tried disassembling the throttle body to remove and test the IACV. Maybe that's something I could manage, though.

The incense idea is genius. I tried it. Some smoke came out of the oil filler port with the cap off; with the cap on, it was primarily coming out of a rectangular hole between the valve cover and the timing belt cover. See the green arrow:
20210403_201824.jpg


This struck me as strange, but it could just mean I'm still leaking test pressure to places that actual boost wouldn't go. I did try pinching off that hose again (the one I think connects to the IACV), but it didn't seem to make any difference. I do have the PCV hose from the turbo inlet to the valve cover plugged, along with the hose from the IACV back to the AFM (I have the tester connected just after this point).

I might try connecting the tester directly to the throttle body. So far I haven't seen any indication of a leak in the intercooler or its piping, so this might make for a more focused test.

Anyone have any idea how smoke would have gotten to that opening?
 

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Discussion Starter · #9 ·
Usually less than 1 psi. It won't hold much — if I hold the hand valve open for several seconds, the tester gauge gets up to maybe 3 psi.
 

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Something's not right that's a huge boost leak. You need to at least get up to the pressure you are boosting to. What are you using as your compressed air source?
 

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Discussion Starter · #11 ·
Right -- that's why I don't think I have the test set up correctly yet. I bought a 6 gal. compressor from Home Depot, along with a hand-operated valve of the kind often found on air pumps at gas stations. I had the regulator at 50 psi, though I turned it down to 25 to try the incense.

I'm wondering whether it might be easier to close the IACV electrically rather than by trying to pinch off the hose. Anyone tried this? I have an adjustable bench power supply -- just need to know how much voltage/current to use. (Well, will also have to figure out how to reach the connector.) Or do I just have to turn the ignition switch to ACC?
 

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The IACV uses 12v to the centre pin then earths through the RSO or RSC pin on the ECU. It cycles this earthing to adjust how much air can get though. It pulses open and shut rather than adjusts a set opening like a stepper motor. These valves do not seal perfectly hence the reason to pinch or block the hose connecting to it.
 

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Discussion Starter · #13 ·
So I eventually gave up trying to do this myself and took it to the shop I use. I hadn't thought that they knew anything about turbos, but it turned out that they do have one guy who works on them (mostly Subarus). They just replaced a couple of vacuum hoses (including to the VTV), and put clamps on the rubber connector between the turbo outlet and the hot pipe. This fixed the problem! The turbo no longer hisses and the top end is much better.

I had noticed that that turbo outlet connector didn't have clamps on it, but I got preoccupied trying to get the system to hold pressure. I'm not sure exactly how they got it sealed, but they say that it did hold pressure after they did the above. In retrospect, I should have just clamped that connector to begin with — I suspect that was by far the most important thing they did.

Anyway, thanks for all the help!
 

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So I eventually gave up trying to do this myself and took it to the shop I use. I hadn't thought that they knew anything about turbos, but it turned out that they do have one guy who works on them (mostly Subarus). They just replaced a couple of vacuum hoses (including to the VTV), and put clamps on the rubber connector between the turbo outlet and the hot pipe. This fixed the problem! The turbo no longer hisses and the top end is much better.

I had noticed that that turbo outlet connector didn't have clamps on it, but I got preoccupied trying to get the system to hold pressure. I'm not sure exactly how they got it sealed, but they say that it did hold pressure after they did the above. In retrospect, I should have just clamped that connector to begin with — I suspect that was by far the most important thing they did.

Anyway, thanks for all the help!
Thanks for the update really glad to hear you have solved the issue 🙂

When they changed the small hoses on the VTV did they clamp them at all? I'm just wondering if mine need clamping also? I just got a brand new VTV because the old one was broken when I got the car, I added zip ties but I was to scared to pull on them too hard I'm not convinced the zip ties clamp it in any way. I did however replace the hoses to the VTV with new.
 

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Discussion Starter · #15 ·
There are clamps on those hoses. I believe they were already there. I would think the clamps would be a standard part; shouldn't be hard to find.
 
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