Generation III External Engine - Vacuum Leak?
04-28-2012, 09:46 AM
I just picked up a six speed 2000 Camaro Z28 a few weeks back. I'm going over everything that the PO's haven't addressed, and I'm a little stumped by, what I believe, is a vacuum leak.
I found one hose with a 1/4 hole in it, and subsequently replaced it. That seemed to make a great improvement. But, I could swear that I can hear another leak. Here's what I have, and you can tell me if I'm nuts...
When the car is cold, the noise is the loudest. This leads me to believe that the sound is the IAC valve bypassing the the TB. I used a short length of tubing held to one ear as a "stethoscope" to try to pinpoint the sound. It seems loudest between the intake and valley cover.
Is there anything on the bottom side of the intake that would even provide a source for a vacuum leak? Is the intake just that "loud" and resonating the air flow noise to the underside?
I am led to believe that there is still another leak somewhere, as the engine does not return to idle as fast as I feel that it should. That's kind of a subjective observation, I know. But, if I blip the throttle, I expect it to return to idle in 1 to 2 seconds.
Most of my experience is with late model SBC's, so I may be way out of line with my expectations anyway.
Can someone set me straight here?
04-28-2012, 04:34 PM
stock intake or aftermarket intake?
04-29-2012, 09:35 AM
This is the OE manifold for sure. It even has the poor fitting OE air box (the one that leaves a gap between the intake tube and the air box lid). The only thing that I can see that is aftermarket on this car is the off brand "turbo" muffler. I'd like to slice it off and weld in a Flowmaster.
I wish that I had another LS1 to compare this to. My only other experience with an LS motor was my 2000 Silverado. I don't recall there being this much intake noise on that engine. Then again, the 5.3 didn't have piston slap either...
05-02-2012, 03:46 PM
So, I’m thinking that there must be something under or behind the intake that is producing this sound (and I still believe that it returns to idle far too slowly). When I picked the car up it had, what I would consider to be, a fairly massive vacuum leak on one of the hoses behind the TB. The afflicted hose had the appearance of chlorine degradation.
I’m familiar with this type of failure as I work with dairy equipment. Dairies use chlorine in their detergents and sanitizers. When rubber is exposed to chlorine, it turns to what I can only describe as gummy. If you rub your finger on it, it smears onto your skin like tar. This is how the vacuum hose was. In fact, it had collapsed under the vacuum of normal operation.
I would have to assume that most intake gasket leaks develop on the upper port of the intake port, simply by virtue of the inherent clamping forces found in an angled mating surface. I may be wrong, but I speculate that is the case.
So, I would guess that I’m looking for a vacuum leak in one of the hoses. I suppose the most logical approach would be to disconnect and cap off vacuum lines until the sound changes (if it does in fact change). Aside from that, I’m stumped.
05-02-2012, 07:49 PM
Just so that I get this straight...
There are three ports into the crankcase for the PCV system? One on the front of the pass side valve cover, one on the rear of the passenger side valve cover, and one somewhere else?
I checked the rubber "Y" under the cowl. It seemed to be ok. I disconnected the vacuum line going to the "Y" from the TB and capped it off. The idle return seemed ok. Subjectively it seemed better. I still can't physically find the leak here.
Purely for my own amusement, I used the old poly tube stethoscope trick, and checked all around the intake. I hear a hiss coming from underneath it.
So, I ask again... is there anything underneath the manifold that could produce a vacuum leak?
Am I basically just looking at an R&R of the manifold gaskets?
05-02-2012, 07:56 PM
Hang on. I'll get a pic in a min
05-02-2012, 08:00 PM
Right below the fuel line is the "y" on my old motor that goes to the driver side valve cover. It wont cause a vac leak. Who know how long mine was like that. I never knew it til I pulled the motor out and I put that intake like 2 yrs before this
05-02-2012, 08:03 PM
05-02-2012, 08:19 PM
I'll throw this out there since I just saw it a few days ago. On a Professional Products intake and throttle body, the gasket between the TB and intake was sucked in at the bottom of the TB. Similar location, and not easy to spray fluid onto to find it.
05-02-2012, 08:23 PM
Yeah, I checked out the Y in the back. I was able to see and touch it. So, with the motor running I reached back behind and prodded around. No evident leak... unfortunately.
So, there's nothing tucked under the manifold?
My best guess is that it sucked an o-ring in or something. I suppose I need to have a look at the manifold gaskets. Looks like it should be 2 hour job, tops.
05-02-2012, 08:43 PM
Not so much on tucked under. Just the valley cover and 2 knock sensors
Not that bad unless it's ur first time. Worse is the two long bolts in the back. It's fairly simple since u don't have to drain the radiator. Only spot coolant runs is on the bottom of the TB unless someone did the TB bypass trick
05-02-2012, 08:44 PM
If I can find a pic of the inake off I'll post it up
05-02-2012, 08:54 PM
the tube in the port is the one that runs to the side of the TB. i just stuck it there to get it out of the way
watch the oil sending unit on the back. the brake booster tube may catch it and break it off if u try to just yank it out
05-03-2012, 09:39 AM
This will be my first time yanking an LS style intake. But compared to some of the other stuff that I've worked on, I'm not too worried. I'm not a mechanic (anymore) and don't claim to know everything, but it is just a machine.
Thanks for the heads up on the OP sending unit! Are Fel-pro's ok for use on the LS1's?
I suppose this will be easier than my broken glowplug the LBZ.
Purely for your entertainment...
I'll give it a shot this weekend... ambition permitting.
05-03-2012, 10:54 AM
Way easier. I personally have never done glowplugs but I've heard stories for my buddy who own a diesel shop. Once I get home from work, I'll see if I've got some more pics of the intake off in the car. Easiest way to not break the OP is by un-doing the brake booster line. The two bolts on the back suck Bc they hit the cowl or at least they did with my FAST intake. Can't rememeber on the stock since it's been so long ago. My old '00 z28 was all original with 155,000 miles when I bought it so I learned alot from all the parts I put on
05-03-2012, 10:58 AM
If I have an issue with clearance in removing the rear bolts, I could always unbolt the trans cross member and let the engine pivot down and back a bit on the clam shells. I haven't looked too closely at it, but there seems to be a lot of room behind the motor.
Thanks again for the info here!
05-03-2012, 11:09 AM
Its tight. I took this the other day for another post on here. This is the back of my BBK SSI on my '01 SS. Don't know how well u can see everything. I took it from the passenger side. He was also have a vac problem and I assumed it was that small line the way he was talking
05-03-2012, 11:13 AM
Ow, and check out ls1howto.com. ALOT of good right ups