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Fuel leaking into the oil 5.7L Mercruiser 2002 570 hours

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lenny35

New member
Hello to all,
I have a 2002 5.7L Mercruiser MAG with 570 hours on it that has oil leaking into the oil crankcase. I had it to the repair shop (Mercruiser dealer) twice and the first time they said #8 injector was bad and fuel line pressure was bypassing the injector at low idle and/or motor stop and getting into crankcase. The second time (within 30 hours or less) for the same issue they said the #2 injector was bad so they again replaced that one. they suggest replacing all of them at one time as I was told they might all be bad. I understand that to some degree but it seems ironic that it is going from one to the next. At the moment I am planning on purchasing the other 6 and replacing them my self. Here's my question. Before I do that is there other ways fuel can get directly into the oil other than through the injectors? I am also wondering if the fuel pressure regulator may be bad and possibly over pressurizing the system and forcing fuel to bypass the injectores? Any thoughts on this or any other things someone might suggest to check? Has anyone had this issue before? I am new to this forum and I am still searching it to see but so far I have not found anything. Thanks in advance, your time is greatly appreciated. -Lenny
 
Welcome to ME.com

Being as your setup doesn't have a mechanical fuel pump, the injectors are the only common path for fuel to be introduced internally...the only addition would be if the fuel pressure regulator is manifold referenced and I can't recall the setup on that particular engine...

A fuel pressure gauge on the fuel rail will tell you its operating pressure...whether the injectors are leaking requires their removal and testing.
 
Makomark, Thank you for your reply and input. That is what I thought but I wanted to do some research and thinking before I just go on a one track method. Your time is much appreciated. Have a great day.
 
I believe it is a common rail but I do not know off hand if it has 2 fuel pumps. Is there a specific pressure gauge for these marine engines or can I use the same one as a car has. Maybe a dumb question but I have found other things that are marine specific.
 
Found something interesting last night. I am getting fuel in the oil and again I was told another injector had probably failed by the mechanic I called yesterday who worked on the motor the last time to replace the number 2 injector. I now have (2) new injectors in cylinders 2 & 8. Anyway, last night when I was looking at the motor to copy down serial numbers and such I noticed the vacuume line was disconnected from the fuel pressure regulator that is attached to the fuel rail on top of the motor. What effect could this have to the motor? Could this create the fuel entering the crankcase issue? The boat ran fine on Sunday when I had it out or so it seemed to be running fine. Any ideas or suggestions? Thanks again to all who weigh in on this issue.
 
An auto gauge will work...just need to make sure the fittings are compatible or get an adapter...

The vacuum line going to the regulator sets the reference point it operates at....when connected to the intake, the regulator keeps a constant fuel pressure across the injectors...

If the regulator is referenced to the atmosphere, then the pressure difference across the injectors would increase with the engine running...if the injectors are marginal, it is possible this could increase what leaks from the injectors...
 
I'd ask the mechanic why he did not find this, and why a fuel rail pressure test was not done.... if for no other reason than for curiosity's sake.


.
 
this ( mechanic ) might be making work for himself.
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Not all mechanics follow a standard troubleshooting process; visual inspection first, analyse the syptoms then proceed w/tests of suspected parts. Some just replace parts w/o testing because they have limited analytical skills. Anyone can miss the obvious now and then.
 
I talked to the mechanic today and he apologized 7-ways from Sunday for missing the vacuum line connection. He agreed that it "may" be a possibility of the suspect fuel leak for the same reason that makomark describes but he added that the injectors should handle much higher pressures than would be created by leaving the vacuum line off. I think I am going to change oil, verify the vacuum line is attached and do some water testing while monitoring the oil and see if the problem is resolved as it I was told it was after replacing the #8 & #2 injector. I sincerely appreciate all the comments, thank you.
 
One way to verify if vaccum line has an effect is check fuel rail pressure with line connected and then diconnect vaccum line exposing it to atmosphere and check the difference in fuel rail pressure. But I think you have solved the problem IMHO. Good catch.......
 
I'm with MM - I've heard of one injector being replaced for an issue but when more than one is bad it is usual and customary to renew the entire set...
 
Well, it the disconnected vacuum line to the rail mounted fuel pressure regulator was not the problem. Still getting fuel in the oil. Ordering a set of fuel injectors today so I can replace them this weekend hopefully. I'll keep you posted to what I find if anyone is still interested. Thanks
 
OK, I still need help if anyone can offer more. Well I replaced the remaining 6 fuel injectors as I was told by the service shop that that is what they intended to do if I had them do it. Still no good. I still have fuel leaking into the oil. I have been told that the only place fuel can get into the oil is through the injectors or through the fuel pressure regulator. Well after replacing the injectors, all of them, I assume that would be next?? I was told there is no other possible way for fuel to get into the oil. I only have about 1-2 hours at most on the boat since I replaced the injectors and I have 2 quarts of additional fluid in the crankcase. Any ideas of where to go. I know I maybe should bring the boat back in for additional diagnosis but after being told the last 6 remaining injectors neede to be replaced and that would solve it,, and it did not, now I am hesitant to listen to them. Help...please??
Thank you in advance
 
I replaced the injectors and I have 2 quarts of additional fluid in the crankcase.
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That is 2 quarts of fuel! 100% sure it is fuel? Pump out the liquid and pour some into a clean jar and place a lid on it. Let it settle overnight. Or send a sample out for oil analysis for accurate lab results.
 
I`d do the OBD hook up next to see what the computers doing. Any type of regulator connected to a fuel source would be suspect. If the diaphram is ruptured it could draw fuel BUT this would be drawn into the manifold to be burned not introduced into the oil.
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