Smoking

[Scott R]

Well I am hoping this will not result in a new engine, but here goes. 1985.5 supercharged. I am blowing a little smoke under high boost around 6k rpm. When I let the gas off it puffs a bunch of smoke. Blue in color and smells like gas. Any ideas?

[Bob's944]

blue smoke is oil.... black is carbon... white is coolant....

[Scott R]

Yes but, why oil on boost? Also I am running VERY hot at late so I ordered a radiator from Pelican I was going to install it this weekend, but now I don't know.

[javier]

rings are the first thing that comes to mind. Have you ever had the head off of your puppy.

Pull the dip stick, does the oil smell like it has hint of fuel in it.

Also, it's probably compression check time.

[Bob's944]

is your supercharger supplied engine oil? i'm guessing it is, if it was leaking into the intake, then all the plugs may show the same type of fouling?? if only one plug is bad, then you have a problem with one cyl instead of the charger.... just a guess

[Scott R]

OK, update. I pulled the plugs and they are all showing carbon tracing. But no a drop of oil! Very weird. Also I have no consumption from the engine. I also did a compression check just now here are the results.

1. 145 2. 143 3. 141 4. 145

Could this all just be a rich condition at high rpm?

[Scott R]

Sorry, yes the supercharger is supplied engine oil. This stinks, it's never something easy!!!!

[wolfrpi]

Those compression numbers are really low for an N/A

------------------
Erick

86 951

http://www.pelicanparts.com/cgi-bin/pmpre/pm.cgi?action=display&login=aka_951

[Scott R]

My Haynes manual says 145 is the norm, being that it is usually wrong what should they be at?

[Blackfoot]

Originally posted by wolfrpi:
Those compression numbers are really low for an N/A

yes they are. in a healthy engine, to find good compression numbers, take your compression ratio (9.5) and multiply it by 18-19. you should be around 170. if you did the comp test correctly, you are running on a worn engine.

you are definitely burning oil if you see blue smoke, no matter if you think you aren't losing oil.

also, if you are burning considerable oil in the combustion, it acts to lower your octane effect, and in a forced induction car like yours, that's the last thing you want to happen.

[Scott R]

Ok, so the numbers are low, the motor has 130K on it. But I have 0 oil residue on the plugs, I mean none at all. They are in the wrong teperature range but thats it. Also this has all started since I installed my H2O injection system, but it still does it now with the system disabled.

[Blackfoot]

sorry for that bad news, but you have a couple of things going for you. one, burning oil in of itself does not necessarily mean an immediate rebuild is in order. my 951 burns quite a bit (although i can't see smoke), and you may be able to put up with your smoke & adding oil on a regular basis. two, your comp numbers are very uniform, with little variation across the cylinders. at least you don't have a cyl that's say 15% lower than the others. if you don't detonate you may be able to run this way for a while.

[Scott R]

Ok some more info for you guru's. This is now only happening when I run it up to 6000 then let the gas off quick! What I am thinking is that I should remove the supercharger and check the roots and intake channel for excessive oil buildup. I notice now that the supercharger is leaking some oil from the front pulley. I wonder if it's leaking inside as well.

[MAS]

My 87 924S is:

170/175/170/175

Although the Porsche guy a few months back said that this was pretty good. I think that in the mid 160's is more normal.

-MAS

[marksportcts]

Scott, it is unfortunate to say, but your rings may be gone, possibly even the pistons. When I ran my car at 7psi with stock n/a pistons, it knocked. I didn't realize it was that bad until I took the motor apart. I didn't even bother with a compression or leak-down test. All the pistons out, the first 3 shared 7 hairline cracks along the ring land. My friends told me that the exhaust smoked when I revved it.
If you have to rebuild it, get 951 pistons.

[Scott R]

Ok, I made an appointment with a a shop here in Colorado that was mentioned on the 944 garage web page. They are going to do a 100psi compressed leakdown test. Then if necessary they are going to rebuild with the turbo pistons and sleeves if it comes down to that. Basically they will take it apart and build it back up stronger. I asked them about stroker kit, but they recommened against it saying that a lower compression ratio offered by the turbo pistons would do me good on my setup.