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smoke on deceleration

13K views 20 replies 15 participants last post by  billszoo1 
#1 ·
after my 350 sb (vortec heads, mild cam) has been out on the highway for about 30 miles (at 70 mph) a bunch of smoke comes from the tailpipes on deceleration onto an off ramp. i rarely take it on the highway, it sees mostly in town driving. the bottom half of the engine only has about 12k miles on it, while the vortec heads have about 22k miles on them. the car never uses oil and doesnt smoke in town unless i slam it to the floor, which puffs out a tiny bit of smoke. i was thinking maybe worn valve stem seals, but, it never smokes when i start it. i have also noticed that after taking it out on the highway there seems to be a litlte bit of oil thats been sucked up into the pcv hose.

does anyone have any ideas on what might be the problem here? i'd like to be able to take 'er ought on the highway without showering the people behind me in smoke when i exit on the off ramps :rolleyes:
 
#3 ·
How can you say rings if he hasn't done a leakdown test?! How bout this, before you take this dude's advice and go ripping the entire motor into pieces because it needs to be done "ASAP," do a little checking first to see what your problem is. My experience is not really that extensive, but if I saw a motor puff off some smoke when its rapping DOWN the RPM's, I'd say valve guides and or seals, not rings. If I see a car idling warm with a continuous stream of light blue smoke coming from the pipes (especially if its just one pipe) I'd say rings.

Do a test, stuff some steel-woll in the PCV baffle (to keep it from sucking up your oil) and take your time, could be a number of things.

K

PS, re-reading your post I'd say PCV almost for sure.

K
 
#5 ·
My experience with smoke on decelleration has always been a problem with valve seals. Also, the times I have had this were all on different SBC with various cubic inches. PVC valve problems can also cause this smoke.

In addition though, I also had blue smoke during a cold start for a few seconds but you don't seem to be having that.

Anyway, the valve seals are pretty easy to look at. Pulling one valve seal will tell you if they have hardened over time, and if so it is replacement time. Easier than a ring job or a total teardown when you might not need either one.

Chev283
 
#6 ·
Somkin' in the Boyz room

Doc here:pimp:

First, Let's determine the Color of the Smoke....

Comes in 3 designer colors...White (usually cooling related) Black (Usually Induction related) And the ever popular ... Blue, Blue/grey ( oil related )

Which is yours?

Is it Black when you Stomp it, Then Blue on shut Down?

If so, you may have a rich Condition on top of Bad Valve Seals/guides. My experience has almost always been Bad valve seals/guides with Smoke on De~acceleration.

If you Suspect a malfunctioning PCV, simply plug the Vacuum line and drive it a few miles See if the condition goes away.

The LEAST likely Cause will be rings ... most notable as "Killer" said Steady "Blue out the Back" regardless of engine demand.

Plug condition will tell you a lot too...

Doc:pimp:
=======================

Death is just nature's way of telling
you to watch your airspeed.....
 
#11 ·
Valve seals bad and check the guides.

Troy
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#12 ·
skizot said:
the bottom half of the engine only has about 12k miles on it, while the vortec heads have about 22k miles on them.

Doc here::pimp:

He said , The Bottom end is fresh at 12k and the Vortec heads have about 22 k miles on them, and who knows how long they have sat around drying up seals, waiting to be installed...OR what they went through on the donor car.

My opinion, I agree with Troy~Curt ... look at seals / Guides , If the PCV doesn't stop the problem.

Doc:pimp:
===================
Twin Engine Airplanes are very safe.
There's always enough power in
the remaining engine to take you
directly to the crash site.
 
#15 · (Edited)
I replaced the PCV valve about 4 months ago (when I was last trying to diagnose this problem). One of my friends suggested that I get one of those crankcase evacuation kits made by Moroso to aid in removing the gases. Does this sound like it would fix my problem?


Also, I've got the vacuum line that's going to my PCV valve T'ed, with the other end going to my power brake booster.
 
#17 ·
decelleration smoke

When you decel. fast the vacuum jumps up high. Sound like trans fliud, or brake fluid coming through the booster. I take some long trips and watch the fluid lost-age.
 
#18 · (Edited)
PCV

Doc here:pimp:

  • Look inside the Vacuum hose or tee to the booster / PCV........ Is it
  • Oily inside?Check the inside of the air cleaner also, Is it Clean and dry... any oil in there?

    If not, move on CUZ it Ain't Suckin' oil....

    [*]The only way you could get Trans Fluid into the induction system, Is if the Transmission modulator Valve was shot......It would smell Sickly sweet And blow tons of white smoke all The time.....Also evidenced By poor Shifting and Loss of ATF.

    [*]If the Power brake booster Were passing Brake Fluid to any degree, you would have decreased power assist (and it would run like crap in a can), and if the master Cylinder Was leaking that badly, By now, probably little or no brake pedal....Besides the Fact... The Brake Booster Has a check Valve (one way valve) At the Booster It would have to pass backwards through...

    [*]If It were Fuel mixture (Carb) The Smoke would Be Black (or a shade of Black) and Smell of raw Fuel. It would Smoke on hard Acceleration, Not So much on De~acceleration...The Pipes (and Plugs) Will Be Dark and Sooty Black (if you put you finger inside the pipe you'll get soot like from a fireplace Chimney.)

    You Mentioned you had a Vacuum Gauge installed, Does it "Bounce " rapidly Between 10 and 20 Hg at idle? or in all driving ranges? It should drop on Acceleration and return at speed, and hold relatively Steady at steady throttle...If not this is a good indicator of Seals/ Guides or Valves.

    You never answered back about the
    COLOR Of the smoke so we are all going on the assumption that it is Blue / Blue~grey Is this accurate?

    You said "It never uses oil" Does that mean... 1/2 qt every Three or four tanks?? ... or you have never had to add oil? Seals don't usually Consume Large quantities of oil (unless excessive wear is present) To make smoke...

    [*]What do the plugs look like, Black and Sooty? Gummy and oily? Clean and white??

    [*]Do a "Wet" And "Dry" Compression test... note major differences Between the two.

    What is the history of the Vortec's? Have they Sat in somebody's garage after 22k of use, for a few years until you came along and scored them?

    If so the Seals Could be dried up, cracked or just shot...Do you know about the engine They came from? Did the Guy run oil like my Girlfriend....30 Grit....and never change it...?

    Have you tried a "Good" oil additive / Sealer for Oil Consuming engines...? Might be something to try, to see if it stops.. and if the seals are just real dry, they might just expand and do their job.

    Doc:pimp:
    =======================
    "A human being is the best computer
    available to place in an Aircraft. ...
    It is also the only one that can be mass
    produced with unskilled labor."
 
#19 ·
smoke on decelleration

I just caught your post and wanted to throw this in. You said your power brake vac was on the same hose and teed off. There is a possibility that it is sucking (especially on deceleration) brake fluid from the vac. The power vac could have a small leak from the master cylinder and it is getting in when you are letting off the gas. It doesent have to be a big leak( you may not notice that much loss in the master cyl.) but it is possible and will drive you nuts trying to find it. Check that side of the hose for wetness from the vac. Just to make sure before you do some uneccesary repairs. Good luck
 
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