Dyno and Exhaust Smoke

JohnyD05 · May 3, 2009

I had the mustang dynoed yesterday.
It put down 248.8 HP at the wheels and 296.7 TQ. I was pretty happy with the power for an N/A motor.

Problem is I see some black smoke at higher RPM which I believe it is running rich and using the stock computer tuning. What scared me though was I was seeing blue smoke (oil burning) as soon as the dyno operator let off the gas and the engine was spinning down on the dyno. There was a pretty significant amount of smoke. on the 2nd and 3rd pull it was same thing. It continued with some blue smoke idling for 20-30 seconds or so. The car has 96k miles on it and has not been driven easy.

Are the rings worn?
Someone said it could be a bad PCV valve so I replaced that today. But I have no way to tell if I have the same problem.

HELP?!

bhuff30 · May 3, 2009

Most likely, it is valve seals. The high intake vacuum from idle and decel in gear tends to pull oil past old valve seals. If you start to notice it a lot at idle, you may want to replace them, but in normal driving, it may not cause much trouble. If it is the valve seals, it is not related to being driven hard, but just the age of the seals.
The black smoke is definately from running rich. The stock tune in my 97 is pig rich up top and it just gets even richer when the computer sees higher than expected airflow (ie, other airflow mods). Get a tune and you can probably pick up a bit more power.
Mind posting up a dyno sheet?

stang74 · May 3, 2009

I noticed that on mine too, the blue smoke when the operator lets off the gas. My car has only 10k miles I doubt the valve seals are going bad..

JohnyD05 · May 3, 2009

1999 Mustang GT
Dark Green
5-Spd
Leather and all the options

Pypes Catted X pipe
Mac flowpath cat-back with 2.5 inch tips.
Steeda Underdrive pulleys
Densecharger CAI
Ported and polished upper plenum
75 mm Throttle body
Stock Timing

Bullitt Suspension (shocks, struts, swaybars and Springs.)
'03 Cobra Brakes - Front and Rear
Steeda Tri Ax

Someone said that cause I let the car sit in the garage for the winters the valve seals could of dryed up.

bhuff30 · May 3, 2009

The car is 7 years old and obviously doesn't get driven much. It is because of age, not mileage.

stang74 said:
I noticed that on mine too, the blue smoke when the operator lets off the gas. My car has only 10k miles I doubt the valve seals are going bad..

MaxedGT · May 3, 2009

A little valve seal leakage isn't anything to worry about, as long as you don't go through a lot of oil. If you go 1000 miles before adding a quart you're more than fine.

Don 95Vert · May 4, 2009

As far as the black smoke goes.... I assume they were using a wideband on the dyno. If so, what did it say? I would not say it DEFINATELY was running rich - because a car that's running lean could do that. How? When an engine detonates, and often before you can even hear it, you see black puffs of smoke coming from the tailpipe at higher RPMs. As a tuner, we use this indicator all the time - if we start seeing black puffs of smoke at high RPMs, even if we don't hear anything - and often we can't especially with loud exhausts, we know it's time to abort the run and change things up a bit in the tune. Could also be something as simple as carbon deposits burning off...

JohnyD05 · May 20, 2009

don there wasn't any kind of A/F on the dyno. It was at a car show with a mobile dyno. All I can say is hopefully it wasnt running lean! At some point I will prob go for a dyno tune.

First I think I need to get the valve guide seals replaced.

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