A little oil smoke

[gothicsera]

I noticed the other day that my '95 K2500 with 350 TBI smokes a little bit when you lift off the throttle. Not so much when you are driving, but if you rev it and then let the rpms drop it does give off a little bit of blue smoke.

So it's mainly under high vacuum that it does it.

The truck's only got about 130k miles on it, but I don't have a lot of history for it.

Would I be right in thinking that this could be as a result of:
Failed PCV valve
Worn valve stem seals

Anything else I should check out?

 

[Ironhead]

Do a compression test. Engine warm, throttle blocked wide open. Do it dry first, then on the second pass, squirt a bit of oil in each cylinder.

If you have good solid and high readings on each cylinder, it is probably not the valve stems or the rings. If the compression goes up quite a bit when you put oil in, it is indicative of bad rings.

If your engine passes the compression test, you are lucky. Now it could be PCV system, or possibly bad intake valve stem seals.

 

[slowburb]

What he said.

 

[michael hurd]

Bad valve stem seals or perhaps intake manifold gaskets are toast, and sucking oil in under high vacuum conditions.

 

[gothicsera]

Thanks guys. I'll run a compression check on all the cylinders and go from there.

When I changed the plugs last week they were all clean and 100% oil free.

 

[Ironhead]

One more thing, well, two actually: I'd measure how much oil it uses, by recording the mileage whenever you have to add a quart; and the second thing is that unless the engine performance is suffering, it is a lot cheaper to add oil from time to time than it is to get into an engine...

 

[gothicsera]

I was going to pull the heads and do some work on the motor anyway as the truck seems way down on power compared to what it should have.

Might even end up ditching the TBI and going down the carb route.

 

[gothicsera]

OK, done a compression test on all cylinders.

They are all 170-175psi cranking with throttle wide open. So they are all even. Sound about right?

 

[skylark]

Good compression. A tbi isn't really a power house. The cam is a small turd. You can warm it over with the usual hot rod tricks but it still isn't going to impress anyone who has had more powerful vehicles.