Smoke (MFI)

My Carrera 2.7 (MFI) has been bit a little smoky since the day I bought it twelve months ago. But now, when it's dead cold, the engine will emit clouds of blue smoke during the initial warm-up cycle (60 seconds); some cold starts are better than others, but there's always blue smoke until it's warm enough to back out of the garage and to drive. It's never been this smoky (when cold) before.

Once I start changing gears, the smoke returns, but only when I apply the throttle after a moment or two of throttle inactivity; the smoke is not as blue as it is during the warm-up cycle, but it's not as black as it should be if the smoke is related to the fuel mixture. It's always been like that, but now it seems worse than before. I've been told to allow for a bit of smoke with early 911's, but this is getting embarrassing. Let's say I turn into a main road, rev it to about 4-4,500rpm, and shift into second: I will always leave a puff of smoke behind me. I used to think it was entirely related to the way throttle is applied: stabbing the pedal as opposed to a slower, more modulated technique; but sometimes I get a smoky surprise when adopting the modulated technique, but only in first gear. When I engage in a bit of hard-charging stuff, say if I want to redline it in second, smoke will be spewing out of the tailpipe until I lift off the throttle, or until I change into third. Then there are times when I ease off from rest: I leave a little cloud of smoke behind before I lift my foot off the throttle while changing into second.

Now, since I'm not leaving behind a constant haze, then it can't be that bad; it's actually okay if I'm doing some cross-country driving as the throttle is not used as an on/off switch as with city driving. A mechanic-friend of mine, who used to work on old MFI BMW 2002's, seems to think it has something to do with fuel delivery shut-off when coasting or going downhill, and the storage of fuel accumulated during periods of throttle inactivity. I have only a vague idea of this system works (shame on me); the guy also said I could have worn valve-stem seals or valve-guides, but I do not want to entertain such thoughts right now. That's not to say that it's not an oil-related problem, but I'd rather rule out a fuel-related problem first! I must admit, I'm having trouble shaking off the thought that I may have bad ring, but I'm willing to be talked out of that thought!

The engine was rebuilt 100,000 kms ago, and I'd like to think that stuff like valve-stem seals, valve-guides, and rings were attended to before the engine was put back together.

So, what the heck is wrong with my engine?



[This message has been edited by Matt Holcomb (edited 04-02-2001).]

You need to chart your oil consumption. That will tell you right away if it is a fuel problem or actually oil being burned. As much as you may not want to hear it, the guides/upper end is probably where the problem lies. Good luck.

If you're burning that much oil the rear of your car will be coated with it. If it is fuel you should be able to smell it.

I'm burning quite a bit of oil - 2 quarts in under 500 miles, but I have a lot of little oil leaks to take care of, so I'm not sure exactly how much oil it's really burning - yet.

I can certainly smell fuel when I start the car cold, but that really doesn't tell us a lot; well, it's looking grim fellas!

I'll have an update soon!

Thanks guys!

Matt, my oil consumption was about 1 quart per 200 miles. I know your embarrassment about the quantity of smoke because I felt the same way. On my engine('88 3.2) when I removed it 2 weeks ago for rebuild this is what I found: All guides severely worn. ALL valves out of spec and had to be replaced. Pistons and cylinders were fine, although new rings will be used. I went completely into the crankcase and found everything inside in perfect condition. Summary, I could have stopped at the heads and my problem would have been solved. I found though, that once the engine was out, and the heads, piston and cylinders were off, it was really straighforward to check and refurbish to bottom end. I now have an engine that runs perfectly, was checked top to bottom, for a very reasonable cost.

By the way, I had no oil 'film' on the back of the car due to burning. It just simply blelched blue smoke at the most inopportune times.
Tom

Matt,

Depending on whether or not the latest 'orange' valve stem seals were used in the rebuild, or not, you may have already worn out another set of valve guides! The exhaust valve guide 'play' should be checked ASAP ... at 10 mm lift, press sideways on valve tip with large screwdriver to see if any noticeable play is present. Do it one side at a time after jacking up that side to minimize oil loss.

The blue smoke certainly doesn't sound like the rpm 'switch' or closed-throttle microswitch could be causing a problem with too rich mixture on overrun above 1800 rpm!

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Warren Hall
1973 911S Targa

wasted fuel creates black smoke. oil and water vapor come out white or blueish. sounds like the engine is getting old. check your oil for heavy fuel dilution. some poorly setup MFI engines run so rich that you can have a crankcase full of gasoline.

Hello

Check your Oillevel and how much fuel is in the oil. Read all MFI technicals on

http://www.pelicanparts.com/techarticles/911_MFI/TipMFI.htm

Grüsse

Guys,

As I've seen his car first hand, I know what Matt is experiencing! I wish I could share his pain...

It raises a question that I've been meaning to ask for a while. I own a 76 CIS 2.7 that has been totally rebuilt (less than 5k kms ago), it has a new pair of crankcases, new bearings, rings etc etc. My oil has a slight gasoline smell to it. I know it's a trait of dry-sumped engines, but I have decided on 3000km (1800 mile) oil changes.

Is this too soon? I'm open to suggestion, but the motor has been freshly overhauled, so I'm definitely looking to protect it. I'm not even sure it's fully run-in, so I'm still taking it easy (as easy as I can! )

I'm fortunate with leakage, as there is none. But when I sniff the oil tank cap (not a habit, I'm over it now!) the smell of gasoline is unmistakable.

Any ideas/comments, guys?

AC



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Adam Chaplin
adamchaplin@optushome.com.au
1976 911S Coupe

Guys,

Thanks for your replies/advice/tips/condolences!

I've just printed out this topic and faxed it to my mechanic.

Stay tuned!

Hi Matt

If your problem persists speak to John Gregory at Spyder Automobiles. He is recognised as the guru for earlier cars, being one of the first authorised (if not the first) Porsche repairer in Australia. Not unusual to see cars sent to him from some of the large P repairers, who use him to fix pre ’85 cars they can’t diagnose. Great guy to speak to and always has time for enthusiasts. I know for a fact he knows MFI inside out. If you want his details please let me know.


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Paul
911T'69

Paul,

John Gregory's details would be great!

Matt, check your e-mail

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Paul
911T'69

Hello

Fuel in Oil is very normal in coldstart runing MFI. But should be avoided.

Fuel in Oil with CIS is an other stroy, check your injectors fast. If not your cylinder will be washed out and start rapid wearing.


Grüsse