390 smoking while holding back

[390owner]

I noticed yesterday while pulling my camper that my 390 is smoking going down hills. I shifted to 3 rd and let the engine hold back the camper. Blue smoke was rolling out the drivers side exhaust. No smoke while pulling or at idle. The engine was built by a professional about 10 miles ago. Any ideas

[My427stang]

Smoking on engine braking is oil being introduced through high vacuum, could be a number of things

- Intake gasket leaking from the bottom
- Valve seals
- Loose guides
- Also could be a PCV getting a dose of oil from an unbaffled air cleaner

If you start pulling plugs you can see how many cylinders are doing it and then start to narrow it down

[cleandan]

Good reply from My427Stang already.
I have diagnosed the wrong PCV valve many times.....remember the auto part stores have gone as universal as possible so the "right" part may well not be so right these days.

Anyway, if your rocker area is being flooded with oil (FE's are well known for this when the oil system is not properly modified), and you are running valve covers that do not have oil splash baffles (or some kind of baffle) and you are running the wrong PCV valve (the weight of the plunger determines the vacuum level when it opens and closes) you could easily be sucking in oil on deceleration because the vacuum is very high at that time, often in the 25+ In/Hg.

Like already mentioned, check your spark plugs to help narrow down the issue.
If all plugs have oil burning signs, the oil is being distributed among all the cylinders...Like a PCV feeding the intake manifold.

If only one bank of plugs has oil it is likely isolated to that side of the engine.
If one plug has oil signs it is likely happening in that cylinder.

[1964Fastback]

I was thinking PCV, possibly combined with too much oil in the heads.  Is this the usual configuration with the PCV valve in one valve cover, breather in the other?  If you can reproduce the problem then I'd try leaving everything hooked up but before you get to the hill, pull the valve out of the valve cover.  If that fixes the smoke, then look at better baffling the valve cover.

10 miles on the rebuild?  Is that enough time for the rings to seat?  Maybe.

Pat

[390owner]

10000 miles. Stock valve civers

[390owner]

Ok I think the problem is the pvc valve. Where do I get a good one or the right one not just a universal

[390owner]

Ok I got my oil catch can installed on my 390 .It has a little air filter on the top of it. It whistles and is driving me crazy. My questions is can I remove the filter and run a hose to the bottom of my air filter on the engine to vent the oil catch can

[RustyCrankshaft]

If the stock PCV valve doesn't work with the current engine build you can use an adjustable one such as:

http://mewagner.com/?p=444

Or use a PCV from a different application that has a different spring.

[390owner]

A little pricey but well worth looking into.

[390owner]

So I have a oil catch can installed on my 390. I also installed a vacuum gauge. When i go down hill pulling a trailer or my camper I usually go to third gear and let the engine hold back to help keep the brakes cool any way the vacuum gets from 20-25 inch pounds then the smoke starts coming out both exhaust pipes. When I get home there is barley any oil in the catch can. Is it just sucking the oil through the can?. If it was the bottom of the intake how can I test this without pulling the intake?

[My427stang]

When the engine was rebuilt, what did you do the heads (guides, new valves, etc) and which valve seals were used?

[390owner]

It has new valves and guides not sure what seals but he usually uses the hood part   I know it has Molly rings

[390owner]

Here is my oil catch can. Do I need the breather on the top or not?https://flic.kr/p/2oQyPTV

[390owner]

IMG_7178 by Daniel Crymes, on Flickr

[1964Fastback]

I would say no to the breather.  Remove it and be sure to plug the hole.  I don't have one on mine.  To me it defeats the purpose of both the PCV system and catch can.  The PCV system because that hose between the manifold and PCV valve is supposed to be air tight with the valve sucking fumes from the engine.  With the breather in, it can also pull in fresh air too, reducing the amount of fumes being sucked in.  It seems like it would also act as a big vacuum leak.

For the same reason, it would also reduce the effectiveness of the catch can.  That's supposed to separate oil and oil fumes from the air being pulled from the valve cover and air coming from the breather would just dilute that.

Maybe I'm not understanding how the breather works on the catch can, like if there's some internal restriction/valve/plumbing and others will jump in.  But my catch can does a pretty good job and is "closed" to outside air.

Pat