I have a 2005 vette with about 82k miles. I bought it 2 months ago and have not ran into any problems at all. I decided that I want some more sound so I picked up a pair of used cats and gutted them out then threw them on. Since then I have found that every time that I release the gas pedal and start to decel there is a small amount of smoke that comes out of my tailpipes. To add on to it, it only happens when the engine is warm and mainly when dropping down from 3k+ rpm. It is very light and hard to see the color but I would say it looks more blue then anything. I have been checking my oil levels a lot and have found that it may be burning a little bit. My question is why would it only start to burn oil when the cats are gutted? Is it because there is no back pressure? Or has it always done that but the cats filtered it?

After doing a lot of research, most forums point to bad valve stem seals, which means having to open up the engine. I don't have much knowledge on this type of job so if anyone could give a ballpark range on price it would be appreciated. And since it seems that this has to be done some point soon I am also wondering what I should do since it is going to be opened up. Heads, Cam, etc.

 

If it's just valve seals, only the valve covers need to be removed. Of course, you need to know what you're doing so you don't drop a valve; if that happens, the heads come off...

Nick

 

If the mole is grey or has a blueish tint it could be the cable seals. There is also the possibility this is oil from the chamber meaning it got past the rings as they are wearing. Probably a good idea to let a shop take a look and get their opinion.

 

Most likely it is valve seals leaking and this is a common thing.

Reason you are seeing blue smoke with the gutted cats is that with stock cats, they are digesting the oil and turning it into exhaust gases.

As for replacing the seals, I don't think most people would consider this as "opening up the engine.

An this is a relatively simple job that you can do yourself with a few tools. To replace the seals, you remove the spark plug wires and remove the valve covers. The valve springs are removed with a valve spring tool. Then it is as simple as using a pair of pliers to remove the old seals. Then use a socket of the correct size and a small rubber mallet to press and seat the new seals. To do this, you need to support the valves so that when the springs are removed they don't fall into the cylinder. To support the valves, a fitting threaded into the spark plug hole is used and a compressed air line is connected to the fitting. Another way to support the valves is to actually used the piston by turning the crank until the piston is all the way to the top of the stroke. The advantage of this method is that with compressed air, if you lose pressure or the line pops of the fitting, the valve will fall. Not so if the piston is in the way.

You can find write ups and videos online on how to do this work.

 

Say what?

Tom

 

The way an advanced diagnostician shall approach this issue (above typical mechanic)
1. determine crankcase pressure and intake pressure during decel
2. Fix PCV system accordingly
3. Fix decel manifold vacuum accordingly (throttle cracker / rolling idle)
4. Ensure complete fuel cut during decel
5. Complete inspection & replacement of ignition & aspirate components e.g. spark plugs & Intake ports & cover baffles for residues of oil and washing them out as needed to reset the engine conditions (fixing the problem by itself is only half of the solution you also have to clean up the oil mess that the problem produced in the first place).

Even if the engine has worn out valve seals this procedure would still work to fix the problem(s) and may be applied to any engine.

 

I would think the diagnostics would be compression test followed by leakdown test.
Had a very similar situation. New valve stem seals. All better.

Luck!