Engine stalling, rough idle, rpm fluctuation.

[rdezs]

.... Same for the dipstick. If it lifts out with absolutely no resistance, time for a new o-ring.

 

[OBSalsoNNBS]

.... Same for the dipstick. If it lifts out with absolutely no resistance, time for a new o-ring.

Dipstick is rather loose. No change in rpm when taking it off or plugging the hole.
I checked the oil filter cap too. I think it fits well and I'm almost sure there was a slight RPM change when taking it off. Tried a few times.

I was referring to the fill tube in my post. It was a wobbly codjer. I ended up taking it off, breaking the locking ring, with the engine running. Doh! Thank God it just fell right down and I was able to retrieve it after searching for 20 minutes for my long reach needlenose...it fits better now but no change in idle roughness.

Anyway, I'm not understanding how the oil orings are related to engine vacuum/idle. Maybe the filler makes sense, but not the dipstick? To me at least.

This is the first modern engine I've run, so hopefully I don't sound like too much of an idiot.

 

[rdezs]

Your PCV system pulls a vacuum on your engine crankcase. It also pulls some fresh air in through the connection on the passenger side valve cover. (The hose usually connects near the throttle body. Some applications directly into the intake tube.) This air is calculated through the mass air flow sensor, which is used in figuring out your fuel mixture along with the O2 sensors.

If the o-ring on the oil filler cap, or the oil filter tube or the dipstick is not sealing, you have additional air entering the crankcase from the outside and not having been measured by the mass air flow sensor. It will give you a slightly lean condition, a change in the idle, etc. That's why you'll notice on a brand new engine, if you just lift up the dipstick an inch it's suddenly acts like a vacuum leak and the idle picks up a little bit.

Now in a high mileage engine with a lot of blow by past the rings, as well as past the valve guides and seals.... It can actually overcome the vacuum from the PCV system. Sometimes this results in idle issues, fouling spark plugs, and the ECM struggling to keep the mixture where it wants it. It also builds up a lot of sludge in the engine. On a well maintained LS engine, that can be at 300,000 plus miles. Eventually the catalytic converters get fouled from too much oil mist from the blow by being burned.

You'll be surprised how much those o-rings really smooth out an idle....

 

[rdezs]

As far as your old small block Chevy with a four barrel carburetor, it's basically the same. There's a vacuum pulled through the PCV valve, and the opposite valve cover draws in fresh air. Only you get to adjust the mixture on the carburetor itself... easy enough to adjust to compensate as the engine wears and the internal blow by increases.

Without this PCV system pulling in fresh air, mixing with whatever blow-by exists, and getting sucked into the intake to be burned.... You would get condensation building up in the bottom of the oil pan, and acidic environment and a buildup of sludge. That's why it's always a good idea on a high mileage engine to periodically remove the PCV hose going to the intake and cleaning it to make sure it's not plugged. You'll note that it should have an insulated cover over it. That's to prevent the water vapor from condensing inside.

 

[rdezs]

..... Believe it or not, every part of that engine has had a lot of thought go into designing various functions. Right down to how many threads do we need on that bolt to hold that item. (And remember, their target for the item to function is as long as the warranty it seems. Think of the LS engine exhaust manifold bolts)

So after digesting all of that about your PCV system, you may ponder why is it necessary to have the amount of vacuum it has. It's because every engine always has some blow by past the piston rings, even brand new. And that amount increases at full throttle. Other than keeping the inside of your engine clean, the other very important aspect is it prevents the crankcase getting pressurized by the blow by gases. If it gets pressurized, it starts pushing those gases mixed with oil vapor out the weakest seals or gaskets. A plugged up PCV is usually spotted first by an oil leak.

 

[OBSalsoNNBS]

Haha digesting is the exact word!!
Thanks for your informative replies! I'm saving this thread. It's impossible diagnose if you first don't understand function.
I didn't realize how technological and involved the 5.3 was compared to my old 350 when I bought it. I really do enjoy it, driving it and the engineering aspect.
And I'm getting new orings and fill tube with my 02 sensors for sure!

 

[rdezs]

If you want to go overboard and be a perfectionist.... I actually have an LS filler cap that I drilled and tapped threads to mount a 4AN fitting. Then I have a 4AN female to a vacuum line hose barb and connect it to my vacuum gauge to check crankcase vacuum at idle and at 2,000 RPM. I like to see about 7 inches of vacuum at idle, which usually nets me about 4 inches at 2,000 RPM, and down around 1 to 2 at full throttle. If you can achieve that, you'll insure no oil leaks from an overpressurized crankcase.

So how do you fine tune it? The newer revised valve covers for LS engines have no PCV valve, but rather a very small orifice. Over 100,000 miles it's normal to have some more blow-by than the new engine.... Removing the valve cover and increasing the size of the orifice with the next size up drill bit, will increase the crankcase vacuum a bit.

 

[donjetman]

That uncontrolled leak at the oil filler cap is allowing UNFILTERED (dirty) air into the engine to wreak havoc on the oil, etc.

 

[OBSalsoNNBS]

If you want to go overboard and be a perfectionist.... I actually have an LS filler cap that I drilled and tapped threads to mount a 4AN fitting. Then I have a 4AN female to a vacuum line hose barb and connect it to my vacuum gauge to check crankcase vacuum at idle and at 2,000 RPM. I like to see about 7 inches of vacuum at idle, which usually nets me about 4 inches at 2,000 RPM, and down around 1 to 2 at full throttle. If you can achieve that, you'll insure no oil leaks from an overpressurized crankcase.

So how do you fine tune it? The newer revised valve covers for LS engines have no PCV valve, but rather a very small orifice. Over 100,000 miles it's normal to have some more blow-by than the new engine.... Removing the valve cover and increasing the size of the orifice with the next size up drill bit, will increase the crankcase vacuum a bit.

I'm far from perfectionist due to lack of skill, but that sounds like something I would do. I do wonder how mine stacks up? How many miles on your truck? There are 156K on mine. I don't have a vacuum gauge...yet!

I had wondered about the PCV valve since NBS LS had them but NNBS don't. Any chance that orifice can get blocked/plugged?

 

[rdezs]

On a high mileage engine with a lot of blow by, yes that orifice can get plugged.