CentralCoaster

Car is up to temperature, and idling. If I bump the throttle, I hear a sucking for maybe 1/4 of a second before the engine noise picks up. Is this possibly a vacuum leak, or just the air intake, or maybe the engine pulling a vacuum on something like the EGR or something?

BTW, I'm under the hood so I'm opening the throttle by hand. It's not a loud sound, but still noticeable.

I replaced all my vacuum lines two weeks ago, and they're not leaking. The only thing I wonder about is if maybe the EGR is leaking vacuum when I get on the throttle. I guess I need to remember when the EGR operates before I can make that assessment though. Maybe its the K&N filter?

Any help? :confused:

ittlfly

You shouldn't be getting any EGR when in park or neutral. So if you are hearing a vacuum loss from there when your under the hood, there is a problem with the unit/ solenoid.

MrNuke

Still sounds like a Vacuum Leak.
You won't hear your EGR at all, unless it is loose.
You could also hear a sucking noise if you are running an open-element air filter right on yoru throttlebody. I have not seen many C4's with that, but have seen TPI engine like that.

CentralCoaster

When is the EGR supposed to open? I'm guessing when engine is above ### rpm and the car's moving 25? mph. And I'm guessing the egr solenoid controls vaccuum to it, (no vacuum = closed) and the egr switch just sends trouble codes to the computer. Am I on track?

Err.. I guess I could go search the archives, but I can't do that when I'm sleeping. -gnite.
:sleep:

Solenoid does sound like a suspect then. I'm trying to track down a rich condition - and the EGR is filling my TB with soot.

Maybe I'll try just plugging the vacuum line to it. The egr only saves me a little gas and makes me smog legal, right?

ittlfly

the ERG operates above 50mph,TPS is between 8-30% open and no more than .4% change in the TPS movement. (taken from the 92 service manual). The solenoid is is controlled by the ECM and allows vacuum from the intake manifold to the EGR valve. If you are hearing a vacuum loss in the area at idle, I'd pull the vacuum lines (to and from the solenoid) and check for leaks / crackes by blowing throught it and plugging the other end.

CorvetteZ51Racer

Does the "vacuum noise" sound likie a quick rush of air, and then it goes away? If it is, what you're hearing is the air going through the choke point on the air filter box. You only hear it for a second because the engine noise drowns it out once the engine catches up in speed.

The EGR open and closed positions depend on year, and can also be tuned with ECM mods. Like someone said before, the ECM controls the EGR solenoid which controls how much vacuum reaches the EGR valve. It's the vacuum level at the EGR valve that determines how far open the valve is.

The EGR will not fill the TB with soot, as the EGR empties into the base intake manifold on the TPI, not into the TB. If your TB is getting filled with soot, it's likely from the PCV system blowing oil vapor into the intake.

TA

If you have opened the lid for your air filter, this can make a sucking type sound :yesnod:

CentralCoaster

I think you're right about the air rushing sound.. probably no big deal.

SH-T! That means my crankcase is overpressurized right? Which means bad rings right? I've heard of some PCV fittings being designed to reduce this pressure. Is this just a quick-fix that'd only mask my problem? I have high oil pressure too. Could blowby be a factor in this? And oil getting nasty real quick?

This doesn't sound good. What are some other symptoms I should be looking for?
:sad:

CentralCoaster

Ok.. I think i was overreacting. I have good compression.

Sounds like my PCV valve is clogged. Stupid little thing can cause such a mess. Also, there's no PCV filter on a Corvette right, because it comes in downstream of the air filter?


[Modified by CentralCoaster, 2:17 AM 3/7/2003]