C4ProjectCar

Once my engine warms up, it develops a pulsating whistle that sounds like a bad accessory bearing or squeaky fan belt. This began occurring immediately after I reinstalled the engine in January. Recently, I finally figured out the cause - a vacuum leak in the crankcase. The second I pull the PCV hose or the breather line on the other side, the whistle subsides, and it immediately resumes when I reattach said fitting. It's pretty embarrassing, especially when I shut off the engine, and the remaining vacuum bleeds off in a several-second-long wail that sounds something like an elk bugle.

I was hoping it was just a leak around the pan gasket, so I put it on the ramps and tightened the pan bolts to spec with a torque wrench. Unfortunately, that didn't fix it. As far as I can tell, this leaves a couple possibilities: the timing cover, either china wall, or the valve cover gaskets. It doesn't sound like it's coming from the valve cover gaskets, and snugging down the bolts didn't help. (The valve covers are quality machined units, and I took care not to overtighten, so warping is not an issue there.)

Of course that narrows it down to the two most difficult fixes. I really don't feel like tearing the whole top end off the engine to reseal everything in hopes of fixing this (especially because The Right Stuff is a PITA to chisel off the china walls), so do you guys have any suggestions of what I can do to pinpoint and/or fix it? It's not like an intake leak where you can spray carb cleaner around and listen to the engine idle - I don't think enough airflow goes through the crankcase for that to have an immediate effect, and I also just don't wanna have solvent sucked into my crankcase.

It's worth mentioning that I slightly bent up the timing cover in the process of replacing the crank seal. I carefully straightened it out, and I laid it on something flat to make sure it would seal. Any remaining imperfections should have been sealed by the RTV I put on the gasket, but who knows.

Edit:
Car is a 1990 base model. The engine has heads, cam, SuperRam, and headers, though the problem began before I installed the headers.

383vett

Normally a leak in the areas you mentioned would be accompanied with a loss of oil. Why don't you do a smoke test with the engine off and the source of the leak should be easily detected?

Tom400CFI

I do. When it's making the noise, take a piece of rubber hose and place it agains your open ear, run the other open end of the hose around the engine. When the open end of that hose zero's in on your dying elk....you'll know it!

C4ProjectCar

Actually, I am losing a bit of oil. Yesterday I saw I was below the fill line. It doesn't drip much, but I can smell it burning off on the exhaust manifolds. I'd chalked it up to valve cover bolts incessantly working loose, but it makes sense that it would be associated with the vacuum leak.

Smoke test? As in pump a bunch of smoke into the crankcase? I do have a fog machine; not sure if that could react with my oil or something.

I meant to mention it, but I gave that a shot. (As an aside, I was amazed how well that let me pick up on the tiniest engine noises!) I couldn't pinpoint it, although it seemed like it was coming from the front/bottom of the engine. If I'm feeling brave this weekend, I might try listening from underneath.

C4ProjectCar

I removed and replaced the intake manifold in the hopes that the leak was occurring at the front or rear china wall, but unfortunately the leak is still apparent. I put my car up on ramps and got under it with the engine running, and it sounds like the whistle is coming from the front bottom of the engine - as I feared, the timing cover.

Not only is the leak annoying because of the sound it makes, it seems to be causing other issues. While coasting, the car's idle swings greatly (approximately 500 - 1400 RPM, IIRC), which I am almost certain is from the vacuum leak. Also, my car has been burning a significant amount of oil: about a quart every 1500 miles. Initially I chalked this up to leaky valve cover gaskets and/or china walls, but I've sorted that out, so I'm guessing the leak is causing too much PCV flow which is sucking oil mist into the intake manifold.

I tried reaching up the front of the engine and smearing some Permatex around, in the hopes I'd cover the leak, but that didn't help. Can you guys think of any solution other than replacing the timing cover gasket?

Tom400CFI

I want to know why a leak to your "oiled areas"/crank case, would have any effect to idle? Or why you're drawing so much air into your crank case that you've got a whistle/hiss that you can hear?

First; your crank case vacuum should be limited to ~9 CFM, by the PCV valve...which ain't enough to cause hissing/whistling that you could hear.
Second, by FAR, the easiest path for make-up air to enter the crank case should be through the nearly 1/2" hole in the ducting that runs from the air TB (air filter, essentially) to the passenger's side valve cover.

If it takes several seconds for your crank case vacuum to subside after shut down....I'd be having a close look at your PCV valve and then the fresh air intake and/or the oil separator on that side.


.

C409

….. As Tom suggested … The way the PCV system is "supposed" to work is to draw fresh air through the engine via the PCV valve on one valve cover (drivers side) and a hose on the other valve cover (passenger side) that goes to the throttle body … if that second hose is MIA or plugged it could cause the vacuum scenario that you are describing … PCV air is a non-metered , but known (to the ECM) quantity and impeding it will affect your idle operation …..

bjankuski

Bingo,
Check the breathe on the opposite valve cover, it sould be open and attached to the throttle body on the port that is ahead of the throttle blades but still filtered. You are getting a vacuum in the crankcase from the PCV and the whistle is air leaking in around the crank seals when the engine is running. This problem will not happen if the breather is hooked up correctly.

PatternDayTrader

Bad pcv valve.
Its stuck open.
You are supposed to have almost zero flow through the PCV during high manifold vacuum conditions. This is how its designed.

Tom400CFI

PCV air is metered, actually, since its' drawing the "fresh air" from the TB...which is after the MAF.

C4ProjectCar

Hey guys, thanks for the responses.

Tom, as I understand it, a vacuum leak can cause a hunting idle. Is that incorrect? I've done my best to understand the PCV system, but honestly I'm a little stumped. It seems like both valve cover lines run to the manifold, where vacuum should be consistent, so I don't get what causes flow. My only thought is that perhaps I missed something, and the passenger side line runs to the throttle body in *front* of the throttle blades?
Also, I'm not sure that it would take that much air to make a whistle. You can place a blade of grass between your two thumbs and cause a pretty loud shriek without blowing too hard.
I've checked the PCV valve, and it seems to be functioning properly: when I blow on it, it allows air through, and sucking on it closes the valve (i.e., it allows air to leave the crankcase but not to enter).
I'm not sure what the fresh air intake and oil separater are; are these possibly equipment found on a different-year car? Mine is a 1990.

C409, both hoses are present. However, I'll have to check, but I'm nearly positive the PCV valve is found on the passenger's side with just a regular hose connector on the driver's side. Is this backward?

Tom400CFI

This is correct. But the PCV system is accounted for in the fuel metering and shouldn't be a vacuum leak.


Correct. The PCV line from the right side goes to "atmosphere". In old carbed cars, it would just plug into the air filter housing. In more modern cars, like yours, it's plugged into the air duct, after the MAF. On the TPI and LT1, they ran it into the TB for "cleanliness" (aesthetic reasons), but the function is still the same and it's pulling air from ahead of the throttle blades....you're correct.


You're right about this too...but the fresh air side inlet (on the pass VC) should be essentially completely free flowing, so you shouldn't have the vacuum building in the crank case in the first place, to generate a "whistle" through anything.


The valve sounds like it's working, but the other job it has (besides a valve that opens and closes) is to meter air at, like I mentioned above, a max of about 9 CFM. W/o that function, you would indeed have a massive "vacuum leak", and way too much air flow through the crank case. I'd replace the PCV valve, simply b/c you can't test "9 CFM" and they cheap.


The device inside the valve cover where the PCV plugs in and the vent tube on the other side are designed to separate oil/air so that you don't draw oil into the intake. If one of those or the ducting (including the TB port) on the passenger's side were plugged, you'd pull some high vacuum in the crank case.


That's backward. Air go:
Air filter >MAF >TB housing>Hose to passenger's side VC>through "crank case" > PCV valve >Hose to plenum > Plenum/runners/cylinders to get burned...with any crank case contaminates.

Tom400CFI

cardo0

Just curious C4, do have excessive fuel tank pressure when you remove the gas cap? More than a small puff but enough to make your hand wet from the fuel vapor gusting out?

C4ProjectCar

Hmm. I'll have to run out and check, but I'm almost positive my system is set up so that it would be impossible for air to flow that direction. I swear, if the problem has just been that my PCV system is backwards...
You wouldn't believe the amount of stupid problems like that I've had on this car from the PO's mechanic. When I first got it, I had problems overheating, and a new serpentine belt I put on got instantly chewed up. Found out the PO's mechanic put a V-belt style water pump on, which has a different pulley alignment and is designed to spin the opposite direction!

Can't say I've noticed that. I'll double-check when I run out in a minute, but I'm almost sure I've never noticed anything more than a little hiss.


Edit:
Alright, PCV is on the passenger side, and it allows me to blow, but not suck. (On another note, anyone got a good way to wash motor oil residue out of your mouth? Swished some diluted dish soap and I can't say I prefer the taste.)
That would mean air is attempting to flow out of the lower intake manifold, down into the crankcase through the driver's side valve cover, back up through the passenger's side valve cover, and into the throttle body. That's the opposite of the above diagram. So I guess I need to switch the PCV valve to the driver's side?

cdm747

These are pictures from my 88 which should be the same as your 90.

Passenger Side


Driver Side With PCV Valve

C4ProjectCar

Thanks for the pics, cdm. I went back and looked at pics from shortly after I got the car, and mine was wrong even then, so I guess I've been operating without a proper PCV system for 4 years.

I'll be darned. Swapped the elbow and the valve, and the squeak seems to be gone. Granted, sometimes it takes a little while to show up, but since I determined it's vacuum-related I am certain that fixed it. Might just be me, but driveability feels a bit better too. Seems like the stumble that made starting from a dead stop difficult has disappeared, but maybe I'm just imagining that. I hope I don't see an oil leak from where the vacuum sucked a gap in the timing cover gasket.

As mad as I am at whichever of the PO's mechanics screwed that up, I'm just as grateful to you guys for helping me sort this out. You have no idea how annoying this noise was, and it was also a bit embarassing to have a car I put so much work into sound so ill-maintained. Just wish I would have caught this before I drove 3000 miles across the country.