travisgreen

if you think it may be leaking or suspect you have another leak that could cause the issue too. pressurize your intake and test for leaks first since that's easier and less invasive

divil

I didn't have much luck with the intake pressure test before. I could not get it to hold any air for more than a few seconds. It was strange because I knew I couldn't have a vacuum leak THAT big, or the engine would surely have been much worse. It seemed to be coming from the rear of the intake somewhere. A lot people seem to run into this problem. Maybe you need a really big compressor. I read that the AOS seals typically leak under pressure and only seal under vacuum, but I couldn't tell exactly where the air was coming from.

Can the position of the factory boost/vacuum gauge indicate a problem? Mine does not sit at the exteme left when idling - it's a little to the right.

travisgreen

As far as the gauge I wouldn't worry about, they are far from accurate. As far as the pressure test there's a few things you can try,

Bypass the aos when your doing the test, pull it from the j boot and plug the hole of the j boot where it was. Then you can narrow down leaks much easier

If your doing it with the aos hooked up, make sure your oil cap is on tight. But whenever I pressurize the system I bypass it

User 52121

I have a cheap 5gal compressor I bought at a local Farm&Fleet 15 years ago.

You really shouldn't have anything coming out of the AOS. Nothing you can hear anyways. If you can hear ANY hissing then you have a leak somewhere that shouldn't be there.

Note that the sound of the hiss echoes really well... I learned that when chasing after everything on my car. Stick your head down in there to listen more closely. Stick your head in various places. I thought I heard a leak coming from behind the intake manifold but it turned out to be a pinhole in the ICV hose where it connected to the manifold. The leak was on the underside and the sound was echoing from under the manifold.

travisgreen

I only bypass AOS when doing pressure test when im pressurizing to 20 PSI, a lot of times the aos will leak under 20 psi but never leak under vacuum. its much easier to hear other leaks when its bypassed and not echoing in the oil fill

jerome951

Something's wrong, then. It should hold pressure for quite a while. If you can't hear it leaking, you have a large leak somewhere.
I can pressurize my intake w/ my small pancake compressor using the Arnworx adapter to ~10psi, remove it, and have ample time to track down small leaks.

Also, your boost gauge could indicate a problem of not enough engine vacuum due to a leak in the intake system.

divil

OK. Sounds like I need to give the pressure test another shot! It's been a while since I did it.

I seem to remember from Van's video on this on youtube that there was air leaking from the AOS all the time, I think he said this was normal. But I will try it again. One thing I was thinking of was to actually run the car with the AOS connector on the j-boot plugged. If the problem is with a leak in the AOS then that would clear it up. I presume there is no problem with startng the engine like that, just for a quick test?

travisgreen

No just make sure you don't plug the hose from aos

User 52121

For the record I didn't do anything with the AOS when I did my pressure testing. The only reason your AOS would have any pressure is if pressure is leaking past the rings.

divil

It would have pressure if you pressurize the intake, because the AOS is connected to the J Boot.

travisgreen

aos sees pressure during pressurizing intake if your doing it at the boot. AOS never sees pressure any other time it sees vacuum. that's why they are more prone to hearing leaks when being presurized

divil

OK, just did the pressure test again. Firstly, without plugging anything, the air is definitely leaking extremely fast from the AOS. I can hear it hissing - when I unscrew the oil cap the hiss changes pitch and I can hear all the air coming out of the oil tube. With the oil cap on tight, using a rubber hose as a stethoscope, I can clearly hear the air coming from the top of the AOS. There are 2 rubber hoses there, one on the top (which I replaced before), and one on the side which I didn't have a replacment for when I was in there before. But it might be the o-rings that are leaking the air. It empties my 1.5 galon compressor in a few seconds without building any pressure at all.

But, with the J-boot to AOS hose plugged, I discovered my throttle body is definitely leaking, between the casting and the intake manifold. I was never able to find this before without blocking off the route to the AOS...but once I did that it was obvious. I sprayed soapy water on it and it bubbles all the way around the square flange. We are talking tiny bubbles here, but I suppose it still matters, especially since it's over a large area.

Luckily I have a TB reseal kit already so I can get started on that. But it looks like I might also have to do the AOS seals?

travisgreen

well im glad you found the TB leak! its def not going to hurt to do the aos seals, If they are leaking THAT bad then they very well may be leaking under vacuum. If they are leaking under vacuum. altho someone that knows more about the AOS might want to chime in bc im not sure a leak in your AOS will change your metered air or not. it seems to me that it wouldn't but I could be wrong. either way it would be a good idea to change them. do your TB and see how it runs

divil

Well that didn't help at all

Resealed the TB and reinstalled. I did a quick pressure test and the TB leak was obviously gone. Then my home made adapter broke so I didn't get to test any further, but with the AOS line plugged the intake was definitely holding some pressure, which was an improvement.

But on the first startup, the problem was there, the same as ever - zero improvement.

I warmed it up and tried the idle setting procedure again. I think maybe the idle when warm is slightly more stable than before, but still not stable enough to set it with any precision - here's what it's like idling when warm, with the digital tach hooked up. It still jumps up into the high 900s occasionaly. I thought maybe it's doing that in an attempt to correct because it's too low, but turning it up didn't make it any more stable. Next I think I will start it cold with the J-boot->AOS line plugged.

travisgreen

that idle sounds absolutely good to me, am I missing something?