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GT40 Fuel In OIL

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  • GT40 Fuel In OIL

    Hello Folks,

    I have a 2000 model year 196 with the GT40 engine. Recently I discovered that the crankcase was 3-4 quarts over full. It almost certainly is fuel because the oil looks normal but is very thin (not brown/tan in color and not foamy) and no water separated from the oil when left in a glass jar for several days. It also has started idling fairly roughly. Sometimes when you bring the power back to idle abruptly, it will stall. At higher power settings it seems to run normally.

    I have done the following:

    1. Replaced all 8 fuel injectors with new 24 lb Ford Performance injectors.
    2. Scanned the computer for failure codes. No codes are present.
    3. Checked fuel pressure with a gage. Readings are normal per PCM maintenance manual.
    4. Checked vacuum line from pressure regulator to plenum for fuel (temporarily replaced the vacuum hose with a clear hose to visualize any fuel getting sucked into the plenum). No fuel in line.
    5. Checked injectors with a stethoscope at idle. All injectors can easily be heard clicking on and off.
    6. Changed the plugs.
    7. Measured resistance in plug wires with ohm meter accounting for wire length. All wires well within specs per PCM maintenance manual.

    After accomplishing the above, I changed the oil and filter and ran the boat for about 1.5 hours over a weekend. After that time the dipstick showed the crankcase over full by about 1 inch (roughly 1 quart). Has anyone seen this happen? Any thoughts would be appreciated!


  • #2
    Taking a stab at it. But, could you have a sticky injector and when it's off, still under pressure, it's leaking into a cylinder and getting past the rings? Not a mechanic but, about the only thing I can think of.


    • #3

      A leaking injector(s) is what I thought the problem was as well. What are the odds that my new set of injectors includes a leaker?


      • #4
        Originally posted by BigC View Post

        A leaking injector(s) is what I thought the problem was as well. What are the odds that my new set of injectors includes a leaker?
        As far as I know the only way that so much gas could make it to oil is through a injector.
        I would do a compression test just to be sure.
        Also when you turn off the engine does the fuel pressure stay up for at least 10 min?

        Another place where I would think fuel could leak is the fuel pressure regulatory. A bad membrane could leak fuel to the vacuum system. But it would make the mixture way to rich and the engine should die or just burn the addional fuel.
        Bit of a mystery I would say.

        Sent from my SAMSUNG-SM-G870A using Tapatalk


        • #5
          Thanks to all for their responses!

          Compression range is 135 to 150 PSI. I checked the fuel pressure regulator to see if fuel was getting sucked up into plenum by swapping out the vacuum hose to the regulator with a clear plastic hose and ran the engine at various speeds. No fuel in the hose. I guess I will pull the new injectors and make a bench tester to check for one that is not holding pressure.

          The pressure regulator does bleed down over a minute or two. I was thinking the regulator was bleeding down back through the pump because the injectors are brand new but that may not be the case.


          • #6
            I have to do some work on mine later I double check the fuel pressure but I believe it stayed up way longer than a few minutes.
            Further I think this has to happen when the engine is of.
            If compression is good and a injectors leaks (running engine) gas would be burned of or send out the exhaust. You should also see it on the spark plugs.

            Did you have ignition on and engine off for a long time?

            Does your engine have a distributor?

            Sent from my SAMSUNG-SM-G870A using Tapatalk


            • #7
              So I checked on mine I use a aftermarket ECU and run higher fuel pressure. I turned ign. on fuel pressure goes to 48 psi (yours should be around 34 if I remember correctly)
              Turned ign off and let it sit took 35 min. to drop to 15 psi.
              If yours drops way faster I would try to find out where the fuel goes if you think its the regulator you can block the return fuel line to test it.
              I think you have to take the intake of to get all injectors out. If you do so you can save some time by using a borehole camera and leave the injectors in place.
              You can use the priming pulse to fire the injectors.



              • #8
                What is the "priming pulse"?


                • #9
                  Originally posted by BigC View Post
                  What is the "priming pulse"?
                  When you turn on ignition the ecu opens all injectors for one pulse to inject some extra fuel for start up.

                  Sent from my SAMSUNG-SM-G870A using Tapatalk


                  • #10
                    Interesting, I missed that important bit of info (priming pulse) in the manual!

                    I performed a bench test on the original set of injectors today (as I mentioned before, I replaced the injectors with new ones) and none of them leak and function normally . I will block off the fuel return line to see what happens. Thanks for the info!


                    • #11
                      Subscribed. This is really odd and it seems like something here doesn't line up

                      3 to 4 quarts overfull. Of fuel? Hard to imagine the engine operating correctly after that. That's like a 1:1 ratio of fuel and oil; the oil properties would be destroyed and you'd have cylinder wall / bearing damage. Also your crankcase pressures have been off the chart with that much extra volume and I would think you would have front/rear main seal issues. Did you check your PCV would likely show signs of that much does it look? When you drained the oil the first time, it would have reeked of gas...did it?

                      And picking up a quart of fuel in the oil after 1.5 hours of operation? That would be very significant amount of leakage - when it's running. If it's overfueling that much, I would expect the plugs to show signs and the exhaust to smell very gassy from running rich. Does it? How do the plugs look? Even color? Dark? White?

                      The only way fuel is getting in the oil is past the rings. And it has to be unburned fuel meaning cylinder(s) aren't firing - this is line with the rough idle. However, when operating, most unburned fuel will exit via the exhaust system, not leak past the rings and you should smell it. You can get some fuel in the oil when you shut it down from injector leakage but that's not line with the description above. I can't get the symptoms to align....

                      If it were me, I'd carefully look at plug colors to try to reconfirm if you're really getting fuel or water in the oil. From your description above, I agree it doesn't sound like water but it's hard to imagine that much overfueling leading to your crankcase volume increase. It's more likely to be water...and you'd see as milk shake oil. And I have to ask - are you super positive your volume is actually increasing?

                      If you can, I'd also do another compression test and - if possible - do a leakdown test.

                      Super odd. Hard to come up with a scenario that fits the description. Fingers crossed for a happy outcome.

                      Last edited by SilentSeven; 08-17-2019, 11:29 AM.
                      2004 206 Air Nautique Limited - Black with Vapor Blue
                      1997 Masters Edition Nautique - Zephyr Green (gone)
                      1982 Mastercraft Powerslot - gone (and missed)
                      Bellevue WA


                      • #12
                        Silent Seven,

                        I am with you, never had anything like this in my 50 plus years of messing with engines. It can"t be water because it does not look like a milkshake (I have seen that scenario more than once). As I said, the 50/50 mix of oil and fuel (what else could it be) did not separate after a week in a jar on the work bench. I cant say that it smells particularly gassy in the jar (smells mostly like oil to me). I agree there might now be some bearing, ring, cylinder damage but the compression is pretty good for a 1000+ hour engine. I really do not smell anything crazy rich in the exhaust either. There are no leaks at the front and rear crank seals.

                        The thing is, other than a slightly ragged idle, it run fine with good power. The pressure regulator exhibits normal pressures (per the PCM GT40 manual) at speed and at idle. The regulator did bleed down after shutdown so I replaced it with a known good one which now holds full pressure for several minutes. Haven't changed the oil and run it with the new regulator but i doubt that is going to change anything. I have also changed the MAP sensor with a known good one as well but have not run it yet.

                        The PCV valve and hose are completely clear, and work normally. I put a vacuum gage on the plenum and it is very study at about 14 in of mg. I have another boat with the identical engine so I have had the luxury of swapping parts and comparing fuel pressure and manifold vacuum with no difference between the two.

                        I have also checked the resistance of both the air charge temp and coolant temp sensors and compared the resistance the the same sensors on the other boat. All read almost exactly the same value. I suppose it is possible that there is a high resistance (short or chaffing) in the wiring harness making the ECM think the engine is dead cold thus making it command a rich mixture.

                        At the first of the season oil change in May of this year, I changed the plugs. The old ones which were run for about 4 seasons looks really great. After all this has happened, I removed the new plugs and put the old ones back in just in case I had a dead plug in the new set. I also ran a spark test on all cylinders and all are firing normally, at least at idle.

                        Next step is to change the oil and run it for an hour or so to see what happens. This will test the new pressure regulator, the potential of a dead plug from the new set I had previously installed and the known good MAP sensor.

                        If the oil levels rises again, I am going to get an oscilloscope and look at the pulse length and voltage at the injectors. I suppose it is possible that the ECM in somehow holding the injectors open too long at speed. As I said before, I checked with a stethoscope to see if the new injectors could be heard opening and closing at idle, which they were.

                        Thanks for taking the time to respond.


                        • #13
                          I went thru the exact same thing a couple seasons ago. changed the injectors...etc...ended up being a stuck open thermostat...I'm having some similar issues again with fouling plugs, and now wont start, so i'm waiting delivery of a new ignition control module/coil...might have been related? Ran great except for off idle to around 10MPH


                          • #14
                            Originally posted by 93Euro View Post
                            I went thru the exact same thing a couple seasons ago. changed the injectors...etc...ended up being a stuck open thermostat...I'm having some similar issues again with fouling plugs, and now wont start, so i'm waiting delivery of a new ignition control module/coil...might have been related? Ran great except for off idle to around 10MPH
                            Did you experience lots of fuel in the oil?


                            • #15
                              yep. exactly like you're describing. My temp gauge never moved, so i assumed it wasn't working. I had other gauges vibrate wires loose in the past. Didn't think much of it. Boat was always running cold, never got up to temp, so always ran rich