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Old 06-21-2004, 02:16 PM
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smoke on deceleration

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
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Old 06-21-2004, 02:26 PM
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rings. you need new rings, do it ASAP

you have blowby and oil is getting past the rings into the heads
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Old 06-21-2004, 02:33 PM
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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
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Old 06-21-2004, 02:57 PM
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I had a similar problem a while ago.when I came off the gas it would blow white smoke which was leading me to head gaskets .
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Old 06-21-2004, 03:36 PM
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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
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Old 06-21-2004, 05:26 PM
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[color=yellow][size=2]Doc here

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...

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Old 06-21-2004, 05:28 PM
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Valve seals, guides..........................
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Old 06-21-2004, 09:05 PM
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I would guess it is the valve guides and seals. By the time those go out, your rings are most likely bad as well. They both go hand in hand. The moral of the story...time for rebuild.
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Old 06-21-2004, 09:53 PM
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man I seriously doubt a 12 thousand mile motor has a set of rings that are shot. Questionable on the valve seals and guides too unless something is setup incorrectly-

K
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Old 06-21-2004, 10:41 PM
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That's right he said it had 12k on the rebuild.

I think it is questionable about the quality of the rebuild.
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Old 06-21-2004, 10:58 PM
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Valve seals bad and check the guides.

Troy
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Old 06-22-2004, 01:07 AM
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Re: smoke on deceleration

Quote:
Originally posted by skizot
the bottom half of the engine only has about 12k miles on it, while the vortec heads have about 22k miles on them.

[color=yellow][size=3]Doc here:

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
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Old 06-22-2004, 08:11 AM
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The key here is he said it never uses oil. It would sound to me like it could be a carburetor problem. If it was smoking that much on the highway you would notice some oil consumption but since it doesnt try looking into the carb settings.

Ben
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Old 06-22-2004, 08:15 AM
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Replace the PCV before condemning the valves and guides.
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Old 06-22-2004, 11:25 AM
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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.

Last edited by skizot; 06-22-2004 at 11:43 AM.
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