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Need help white/gray smoke... but only with 3" cat-less exhaust

 
Old 05-25-2011, 10:14 AM
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Clown
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Default Need help white/gray smoke... but only with 3" cat-less exhaust

Hi I am just finishing up my 944 Turbo project which I built myself. I received the car in peices having never owned a 944 Turbo or driven one I am often times curious how one should drive and behave. Here is what his happening...

I am getting white/gray smoke out of the back tail pipe of my lindsey 3" exhaust but only after about 20 seconds of sitting and idleing but there is a twist keep reading....

Here is what happens: Come back from a drive around town and pull into driveway. It idles great and sounds great. About 20-30 seconds after sitting and still running it makes a breif regurgitating/quieter rummble sound and then I know what is coming next the white/gray smoke out the exhaust pipe. I can repeat this time after time. I do not see any smoke when I am driving and the car seems to run and idle great to me otherwise...but again never driven one before I rebuilt this one and modified it.....Dont jump to conclusions now.....Here is the catch. I put on the Stock 2.5 exhaust with Catylitic converter and no more smoke no matter how long I drive around and let it sit in driveway running...No Smoke! Kept the stock exhaust on for a few weeks until I recently passed emissions (the first time I took it in!)......Well guess what I just put the
3" lindsey cat-less exhaust back on yesterday took it for a drive brought it back home and yes once again the Smoke has returned after sitting and running for 20-30 seconds in driveway. ??? WHY???
Additional Info: Car seems to be running rich with dark black deposit on tailpipe...

Here is what I have on car: 1987 951 ,Rebuilt 2.5 Longblock, Tial 38mm WG, Lindsey/Garret medium sized turbo (not currently watercooled), Full 3" Exhaust Cat-less), MBC, New Vacuum Hoses, alluminum BOV medium spring, Adjustable Fuel Pressure Regulator, brand new 55# injectors, Max Chips, Lindsey Quad-MAF, Currently running 15PSI

You guys have been a wealth of information thanks for your help!
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Old 05-25-2011, 10:55 AM
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Can you take a video of the smoke? Big difference in potential causes if white vs. gray....
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Old 05-25-2011, 11:05 AM
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Have you installed a new O2 sensor? I had a car doing a similar thing and ended up being a bad O2. And another car that was bad seals in the turbo.

Last edited by PorscheDoc; 05-25-2011 at 11:26 AM.
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Old 05-25-2011, 11:25 AM
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"(not currently watercooled)"

What do you mean? is it a water cooled turbo with out any waterlines connected to it? is the turbo DBB?

Isn't white smoke usually mean H20? ..water not sure what gray is?
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Old 05-25-2011, 11:47 AM
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not sure on the smoke, but just out of curiousity let me know if you want to get rid of the lindsey 3" exhaust, i can test it on my car and see if it smokes
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Old 05-25-2011, 01:46 PM
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Thank you for your replies. I can take video just not sure if I can post video. The O2 Sensor has not been replaced but that sounds like a good place to start. Thanks PorscheDoc.

I just am wondering why aftermarket exhaust would smoke and the stock one does not?? It is not a DBB and has ports for both water and oil but currently is just Oil cooled. I had a problem wrapping the coolant neck around the large turbo and still clearing the intake manifold.....so left it off and converted to oil only. I am thinking the smoke is more white than gray but my gut is telling me it is not coolant but it may be running rich.
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Old 05-25-2011, 02:45 PM
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As far as grey smoke goes that would be fuel I think. Ive seen a 964, I believe it was, that had a bad cylinder head temp sensor (not coolant temp but cylinder head temp) and it was running very rich and smoking light grey/blue/white smoke. It smelled exactly like unburnt fuel though so have you smelled the smoke?

**Edit: but since yours only smokes with the aftermarket exhaust and we don't have cylinder head temp sensors (or do we?) my experience doesn't really help you. Unless its running rich enough that the catalytic converter burns the excess fuel with the stock exhaust and without the catalytic converter the excess unburnt fuel is not burnt and would create a grey smoke...
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Old 05-25-2011, 03:14 PM
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Thats an interesting theory about the Cat burning the excess fuel, but do cats burn any fuel? Anyone live in Connecticut want to stop by and check this car out. I am at a loss sometimes because I dont know how it should feel and have a million questions. The car feels fast but I dont know what stock feels like either. I just am amazed I put the thing together myself and it drives down the road...one step at a time I guess...
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Old 05-25-2011, 03:31 PM
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As slapsalot suggested, what does the smoke smell like? Burnt coolant, oil, and fuel have distinctly different smells.
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Old 05-25-2011, 04:22 PM
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How do you know he slapsalot? Anyway...I can smell the smoke but not sure what either smell is supposed to smell like. I am not a mechanic and this is the only car I have ever owned that smokes. Any tipps?
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Old 05-25-2011, 04:28 PM
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Originally Posted by Clown View Post
How do you know he slapsalot? Anyway...I can smell the smoke but not sure what either smell is supposed to smell like. I am not a mechanic and this is the only car I have ever owned that smokes. Any tipps?
Hahahahahahahah no comment on that.

The job of the catalytic converter is exactly to burn excess fuel and other byproducts of combustion. And I don't know if I could describe the smell of unburnt fuel vs. water vs. antifreeze but someone else might be able to chime in on describing the smells...

The best I can do is, antifreeze smells slightly sour/sweet and unburnt fuel smells like fuel and **** mixed together.
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Old 05-25-2011, 06:23 PM
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Originally Posted by SirLapsalot View Post
The best I can do is, antifreeze smells slightly sour/sweet and unburnt fuel smells like fuel and **** mixed together.
They all taste like chicken!

Any sign of coolant levels going down?
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Old 05-25-2011, 11:29 PM
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Very interesting I suppose the cat may be burning the excess fuel. No sign of the coolant going down so far but have not driven it enough yet as I just got it registered. I may also try replacing O2 sensor. Thanks for your help guys. If anyone else has thoughts please chime in.
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Old 05-26-2011, 12:23 AM
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Is it using oil or water ? However sounds like a turbo leaking oil into the exhaust side . Need to do leak down test or just a compression test to see the cylinder condtion. I had one doing this a few years back ended up being a turbo .
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Old 05-26-2011, 07:37 AM
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Yes I agree the turbo may also be causing the smoke. I really do need to run some cylnder tests soon. The turbo was a used Garrett unit and not sure the condition before I put it in allthough there was no shaft play and upon taking it apart it looked in great condition. How did you determine your turbo was smoking anyway. Is there anyone way without replacing the unit first? C Anderson: Where did you get that front splitter?
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