XtinctZ28

iTrader: (57)

My car will not smoke at idle, while revving, or while screaming at WOT in gear. However, when I am cruising along and down shift to help slow down, especially into second from third, there is smoke coming from the exhaust. It doesnt seem to last for more than just a few seconds, but it only happens while using the engine to slow myself down. Any ideas?

The smoke is greyish in color, and car smells very rich(could be the ORY).

Any ideas would be appreciated.

98 M6 - 59,000 miles

red01z28

iTrader: (9)

it could very possibally be your valve seals leaking a little and letting some oil get down in there causing it to smoke its fairly normal it probally wouldnt be a bad idea to change them

DaddySS

Smoke on deceleration is a sure sign of valve seals leaking. Also double check your PCV, see if you have excess oil in the tube.

1QuickT-A

iTrader: (12)

If you ever let your car sit for a few days without cranking it up you will know if its the valve seals or not.. Cause when you start it up for the 1st time in a while you will more than likely see some "blue" looking smoke from the exhaust and then it will clear up.

BriancWS6

iTrader: (18)

Well explain why my pewter car would do it on decel on the dyno with NEW valve seals that I put in with the cam

BYE RICE

iTrader: (2)

LS1's do that..
Especially older ones(like 98's) that have been beat on..Usually M6's..It's got something to do with the PCV system/piston rings..
My car didn't smoke until I installed headers/ORY & a mild cam.
After that,It did exactly as you discribed..I saw it in my rear view,on the dyno,& friends driving behind me would always comment on my 'spy hunter' mod.
Oil consumtion went up also..
If you were to re-ring the engine,it would go away.
Might as well throw a Lunati stroker bottom end in it while you're at it..

pekkaz

Options are rings, excessive valve guide clearance, PCV... and the seals. I've had bad experiences using ls6 valve seals with 98 heads. New seals leaked enough to keep the exhaust port roofs shiny. Also seal install can go wrong..

XtinctZ28

iTrader: (57)

Okay. First, thanks for all the replies.

When I leave it set for a few days (the last time was 10 days) and start it up, it does not smoke at all. I really has not been beat on. It only smokes when I am forcing the revs down by downshifting then just letting the engine slow the car (from around 4500rpms down to 2000rpms roughly) So does it sound more like the seals, or does it really have to do with the rings?
I will check the PCV also. Maybe its nothing, I'm just paranoid.

Thanks

Tally TransAm

iTrader: (17)

it sounds like the pcv system sucking oil back into the intake

curious as to why you just dont use the brakes to slow down, they are more effiecient, cheaper to replace than say a clutch or piston rings, and dont turn your motor into a 346 cubic inch oil consuming vacuum pump

XtinctZ28

iTrader: (57)

I know I should just brake , usually its because I like the sound(Stupid I know) Thanks for all the input

VSGLS1

iTrader: (8)

PCV. I changed my valve stem seals and PCV after my smoking on decel issues. Problem solved.

XtinctZ28

iTrader: (57)

Thanks for the help. I will do the same and hopefully it goes away.

GuitsBoy

iTrader: (4)

Are you certain that the seals were pressed on hard enough to feel them click? Many people push them on, but not hard enough to have them click.

30th droptop

iTrader: (-1)

Deceleration creates very high vacuum conditions in the cylinder, so oil will be drawn in from wherever it can be (valve guides/seals, rings, etc). I've seen cars where there is no oil consumption at any time except deceleration from high engine speed in gear. It could be that oil is getting sucked past the rings under those conditions, and they're otherwise seating fine.

nytoy

iTrader: (3)

So basically without a leakdown test it's going to be impossible to figure out.

slowta99

right on the money with that explanation, most common is the vacuum is sucking oil right past stem seals,

nytoy

iTrader: (3)

Any update, I'm having the same problem and would like to know before I go pulling the heads apart. Thanks.