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Thread: 911S 2.4: Gas getting into the oil

  1. #1

    911S 2.4: Gas getting into the oil

    As I sit and wait for delivery of my new Glacier Blue "S" I've been reading through the Service Records provide by the Seller (G&W). I noticed that on several occassions the car was found to have a significant amount of fuel in the crankcase (oil). The motor has approx 25K miles on a rebuild with a total of 138K miles on the car. It appears that before the rebuild was done fuel was getting into the oil and after the rebuild fuel was found in the oil again. Each time the shop replaced the "cold start valve". It was also noted that when the motor was rebuilt the MFI pump and throttle bodies were rebuilt as well.

    I don't have a great understanding of MFI's yet, but isn't there a "switch" that shuts off the fuel when the throttle bodies are closed? And if I understand correctly the only way fuel is going to get into the crankcase is through the MFI injectors in each cylinder. So I'm thinking the throttle bodies and/or pump need attention . . . yes?

    An interesting note on one service document said "two quarts" of fuel was found in the crankcase.

    It should be very interesting to see the condition of this motor when it finally gets here (10-14 days).

    If anyone has experience with this I would greatly appreciate any information on this problem.

    After all I was planning to drop the motor . . . now I'm thinking it's going to come apart so I can repair any damage done to the rings/bearings/etc.

    Thanks,

    Tom C.

  2. #2
    The MFI has a cold start circuit that dumps raw fuel into the stacks when you crank it and continues to do so for a few more seconds when a timer shuts if off. You can use the "Check, Measure, Adjust article on Pelican to find the particulars on this system.

    The MFI pump is a peculiar device in that it pumps fuel at a very high pressure through spring loaded valves and always having some pressure on the fuel lines. This presure can seep by the pump pistons and enter the crankcase through the oil that is pumped through the bottom of the fuel pump.

    Having the oil and the gas inside the same device at pressure is a flaw, AFIC. Some racers eliminate the flow of oil to the pump and simply fill it and let it lube itself. Or course, they do a much higher level of maintenance. To me, that would be a way to get by temporarlily.

    I hope that there is no damage to your engine internals, but you must monitor the situation closely. I believe a small amount of fuel is enevitable. Driving untill the oil reaches 180* each outing will evaporate this small amount. Mfi pumps that sit for long periods want to leak fuel into the oil. Mine did, but sealed itself up weel enough that I don't gain any volume in the oil. I lose volume, which is good to a certain extent. I don't have any stats on that as I have spent a lot of time working on the car and not that much driving it long distances. When I do go out, I get it hot and drive it hard. That'll use oil, FS.

  3. #3
    Ok, so that makes sense . . . the oil system lubes the MFI pump as well. So a significant amount of fuel in the oil could also be the result of the car "just sitting" for an extended lenght of time. Or, the car only driven on short trips not allowing it to hit full temp to burn off the fuel.

    I'm speculating here at best, but is it also possible for the injectors to leak gas into the cylinders? This would probably result in fouled plugs and other nasty things that could happen to the piston/rod/etc.

    Thanks Zeke for your input . . .

    Tom C.

  4. #4
    Moderator Chuck Miller's Avatar
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    Tom,


    Zeke is right...

    Even a newly redone MFI system will still contaminate the oil... it was/is always a problem.

    Frequent oil changes are what we do...

    Hopefully your system hasn't washed down and dried out some 'up'n-down & in'n-out surfaces that should be slippery...

    Hope your check finds all your parts OK and reusable.


    When you keep these things up you can flog'm for ever
    Chuck Miller
    Creative Advisor/Message Board Moderator - Early 911S Registry #109
    R Gruppe #88

    TYP901 #62
    '73S cpe #1099 - Matched # 2.7/9.5 RS spec rebuild
    '67 Malibu 327 spt cpe - Period 350 Rebuild

    98 Chevy S-10 Utility
    15 GTI Commuter

  5. #5

    Talking Thanks for the help

    Thanks very much for the input. I actually feel a bit better knowing it is a common thing with MFI systems. So I'll change the oil "muy pronto" and then simply monitor the oil over a period to see what happens.

    Chuck - I've read many of your posts and learned much. I recall you had your motor rebuild recently . . . yes? What shop did your motor? I ask because I will also need some help with mine in the near future.

    Thanks again,

    Tom Ching

  6. #6
    CHange all fluids and the rubber brake hoses in any car as soon as you buy it.

    Avoid driving for less than 1/2 hr at a time -- keep the oil warm and it will volatilize water and gas in it.

    Also, check all the rubber suspension bushings - they are probably ready to be replaced. Enjoy your new car. They don't build 'em like that anymore.

  7. #7
    Originally posted by RandyWebb
    CHange all fluids and the rubber brake hoses in any car as soon as you buy it.

    Avoid driving for less than 1/2 hr at a time -- keep the oil warm and it will volatilize water and gas in it.

    Also, check all the rubber suspension bushings - they are probably ready to be replaced. Enjoy your new car. They don't build 'em like that anymore.
    Amen.

  8. #8
    Moderator Chuck Miller's Avatar
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    Tom,

    I've promised to write a 3 part article in the ESSES about the whys, whens, hows, ...what didn't work, and what did on my rebuild...starting with the issue after the one that's now coming out.

    What I will tell you is that I did the rebuild in my garage at my house with the help of a professional Porsche mechanic who 'freelances' on the weekends. He helps with a small group of client's cars... I feel very lucky to be on the list.

    Give me a PM and we'll talk...

    Cheers,
    Chuck Miller
    Creative Advisor/Message Board Moderator - Early 911S Registry #109
    R Gruppe #88

    TYP901 #62
    '73S cpe #1099 - Matched # 2.7/9.5 RS spec rebuild
    '67 Malibu 327 spt cpe - Period 350 Rebuild

    98 Chevy S-10 Utility
    15 GTI Commuter

  9. #9
    As Randy said, try not to drive the car without getting the oil warm. My 2.4 E had the exact same problem recently when it was in a body shop for a couple of weeks for some touch-up. They kept jockeying the car around due to the tight floor space. When I picked it up the guage was pegged and the dipstick was wet almost to the top. Oil seemed very thin and smelled like gas. Once I changed the oil it was fine and I have not seen the problem come back.
    Tom Morgan
    Charlotte, NC
    '18 Carrera T - R #368, S #692
    1973 Giulia Super 1.3

  10. #10
    Need a sanity check on this topic. So, my engine is newly rebuilt. The MFI wasn't as the PO/Restorer said it didnt' need it. Well come to find out that nobody can tune this engine right. To rich at idle, too lean at midrange. All the settings need reset as it appears they've all been mucked with by who knows. In addition, the engine blows black smoke under acceleration (extra fuel), and white/blue smoke under heavy throttle breaking (at warmed up temps, assuming its oil burning). The PO/Restorer has agreed to check into the MFI and 'make things right'. He pulled the injectors last week and took them to Pacific (gus) to test on a bench. One of the injectors was clogged/bad, spraying sideways??? He says that Gus says that the fuel for that cyclinder would not burn right, excess would drop down into the crank and mix fuel with the oil. Does this make sense? Would this explain the blue/white smoke under decelleration? The car was going through a lot of oil (about 2,000 miles since rebuild, but all miles done with engine poorly tuned, been sticking under 6500 RPM since ~1000miles, under 5,000RPM for first 1,000 miles). I need to know what else to ask, to have checked.

    Next he's going to re-tune/re-set all the linkages, idle screws, etc... to spec, then start to re-tune. I've read all the Pelican Tech notes from Lee Rice. They are great, but I need another voice of guidance.

    I'm on a plane tomorrow am for a few days of FlyFishing on the Green River in Utah, so not sure when I can check for responses before Friday evening. Thanks for the help (in advance).

    Chris
    Chris Purpura @civilizedmisfit
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    72T aka The "Civilized Misfit" Build - Helicopter Cooled! See: https://www.excellence-mag.com/issue...vilized-misfit
    2019 911 Carrera GTS (sold, no regrets)
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