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Thread: '91 M5 Fuel in Oil

  1. #1
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    '91 M5 Fuel in Oil

    Hey guys, just like the title says i noticed that I have fuel in my oil. I pulled the dipstick while investigating a different issue, and noticed the heavy gasoline smell. There is no coolant in the oil, but it is a bit darker in color than usual. I'm going to run a compression test later today, but I'm not sure what else to do to diagnose the issue. I might hop over to harbor freight and grab a fuel pressure tester to see if it might be that as well. Any suggestions?

  2. #2
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    Request an oil test kit from blackstone labs and send in a sample of your oil to confirm suspicions.

  3. #3
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    Quote Originally Posted by jmile46 View Post
    Request an oil test kit from blackstone labs and send in a sample of your oil to confirm suspicions.
    Unless you have other symptoms, OP, I agree with jmile46^ wholeheartedly.

    Give Blackstone your email so you can get the results more quickly.
    - Brent
    www.angry-ass.com

    Quote Originally Posted by danespann View Post
    Every E34 needs the same things in the end.

  4. #4
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    A leaky injector can fill a cylinder with gas while the vehicle is off which can seep past rings. Check that fuel pressure does not drop when car is turned off.

    Fuel in oil is bad for the engine as it dilutes your oil causing increased wear. What's the mileage and maintenance like on this vehicle?
    Last edited by zubbie; 03-15-2019 at 12:34 PM.

  5. #5
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    Quote Originally Posted by BleedsBlue View Post
    Unless you have other symptoms, OP, I agree with jmile46^ wholeheartedly.

    Give Blackstone your email so you can get the results more quickly.
    I'll look into getting this done. I was going to replace the oil and fuel injector o rings to see if that solves my issue. Should I hold off until I have analysis done?

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  6. #6
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    Quote Originally Posted by zubbie View Post
    A leaky injector can fill a cylinder with gas while the vehicle is off which can seep past rings. Check that fuel pressure does not drop when car is turned off.

    Fuel in oil is bad for the engine as it dilutes your oil causing increased wear. What's the mileage and maintenance like on this vehicle?
    I'll grab a fuel pressure tester kit today and figure it out. Thanks for the advice. I was going to replace injector o rings and oil to see if that helps at all or if the oil gets dilluted with fuel again.

    The maintenance was kept up with by the previous owner, but it seems like it's rarely been driven in the last 8 or so years. He gave me extensive records of service performed. What services should I look for in the records? It currently has 127k miles and had 120k when he bought it in 2011.

    Sent from my ONEPLUS A6013 using Tapatalk

  7. #7
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    Replacing the injector o rings isn't going to stop the fuel from leaking into the cylinder. Yes the o rings should be replaced assuming that they have not been replaced recently and you will need to disturb them to remove the injectors for testing but o rings are not the source of your problem. A bad o ring would allow unmetered air to be sucked in around the injector, causing cylinder to run lean. What seems to be your case is the injector is failing to close fully close internally (it's just a valve with a nozzle). When the engine is running, it probably isn't affecting much but after the car is shut down the pressure in the fuel rail is leaking thru the injector and ultimately into the oil. You can jury rig a bench tester to find the leaking injector. Check youtube for videos.

  8. #8
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    Quote Originally Posted by gdavid View Post
    Replacing the injector o rings isn't going to stop the fuel from leaking into the cylinder. Yes the o rings should be replaced assuming that they have not been replaced recently and you will need to disturb them to remove the injectors for testing but o rings are not the source of your problem. A bad o ring would allow unmetered air to be sucked in around the injector, causing cylinder to run lean. What seems to be your case is the injector is failing to close fully close internally (it's just a valve with a nozzle). When the engine is running, it probably isn't affecting much but after the car is shut down the pressure in the fuel rail is leaking thru the injector and ultimately into the oil. You can jury rig a bench tester to find the leaking injector. Check youtube for videos.
    Ah, that makes sense! Would the faulty injector be easily repairable? I was thinking about just replacing the whole set.

  9. #9
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    You can run fuel injector cleaner through them to some avail (with them out of the car, look for videos), it may be enough to get the faulty injector sealing again but the best route would be either sending them out to be professionally cleaned or replace them. The really can't be rebuilt as they don't really come apart, you can replace the o rings, spacers and caps (if they have them, I'm not familiar with yours) but the internal mechanism can only be cleaned by flushing them out and through ultrasonic cleaner.

    When you pull the injectors out, you may be able to tell which is leaking if you look and smell carefully. Also bleed the pressure off of the fuel rail before you start pulling injectors to avoid dumping the residual gas down the side of your engine.

    On second thought, I believe this is a pretty rare and expensive engine you have, the safest route would be getting a new set from a reputable vendor.
    Last edited by gdavid; 03-15-2019 at 02:27 PM.

  10. #10
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    Quote Originally Posted by E34M5ProjectCar View Post
    I'll look into getting this done. I was going to replace the oil and fuel injector o rings to see if that solves my issue. Should I hold off until I have analysis done?
    I sure would. It's easy to throw money at it, especially if you're in a hurry. While the advice in the thread so far is tracking in the right direction, if you actually have fuel in your oil, I would want that blood sample first before replacing anything. Again, unless you have other symptoms.

    S38 money escalates quickly, my good man.
    - Brent
    www.angry-ass.com

    Quote Originally Posted by danespann View Post
    Every E34 needs the same things in the end.

  11. #11
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    What's been said above.

    Blackstone labs are in Indiana, you can go on their site and prepay for the analysis, $28. They'll email you an order number and send you the kit which is prepaid for return postage. Fill the sample bottle, pop it back in the container and send it straight back. It usually takes them around 3 or 4 days to get the analysis back to you via email. We do it with the race cars after every event, the more info you give them the better they can help diagnose any issues.

  12. #12
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    not an m5 guy myself...

    can you remove the injectors while still maintaining fuel rail pressure? Then you can easily see if one injector drips when the engine's off. A leak, in conjunction with fuel rail pressure dropping, would be conclusive.

    as for injectors, there are plenty places that will ultrasonically clean, then bench test your injectors, giving you the results. Or they will match injectors for you and give you back a set that are close to each other. How close is close, I dunno, but theoretically the closer the better.

    If you have access, reading the fuel trims for each injector may also be of use. One injector badly out of whack versus the others would point to a problem.
    Charlie

    Your mission, should you decide to accept it, is to add value to these threads, either by pictures or by descriptions, so the next person with the same or similar problem stands on your shoulders.

  13. #13
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    I would definitely do the analysis if its really that cheap. FWIW, injector servicing is fairly inexpensive. There are loads of guys on ebay doing it. For less than 100, you send them your injectors and they clean and flow test them.
    -Alex

  14. #14
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    Why waste time with an oil analysis ? There is fuel in the oil, and it didn't get there from the oil or the metal in the engine. Could have only gotten there from the injectors. There are two ways to check this. First shut down the car for the night. Next morning, pull out all the plugs and stuff a hose down each one and sniff. You should not get a strong smell of gasoline from any of them. A trace - maybe - old injectors will be very slight leaks, but nothing strong and unmistakeable.

    The second way to check is much easier. Shut down for the night after a drive, then next morning, unscrew the holding bolts for the fuel rails and lift it up a few inches )that's the furthest they will go. Prop it against the manifold with something. Put a hose down each injector port and sniff.

    Third way is to lift up the fuel rail slightly and put a paper towel above each injector port and lightly place the rail and injector tips on it. The next morning, remove the paper towel and see where the leaks are at and how bad they are.

    After fixing this, change the oil if you are due for an oil change. If not, just run the engine at idle ro go for a short drive, and then remove the dipstick. The heat will cause all the fuel to vapourise and vent out either through the ccv during driving, or through the dipstick tube when the dipstick is removed. The oil will be thinned down a little but its not a showstopper.... it takes very little gasoline to produce a strong smell in the oil.

  15. #15
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    So, an update on the fuel problem. I think there was fuel in the oil because the car had been sitting for a while before I bought it. I ran a cold compression test, and came back with numbers between 130-140psi on each cylinder. I gave it a fresh oil change and checked all the fluids. I decided I would drive it around this week to see if the issue returns. So far everything has been great, and the car runs like a dream!

    Edit- I check the dip stick everyday for any gas smells, and there doesn't seem to be an issue.
    Last edited by E34M5ProjectCar; 03-21-2019 at 09:59 AM.

  16. #16
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    Quote Originally Posted by Thomas525 View Post
    Why waste time with an oil analysis ? There is fuel in the oil, and it didn't get there from the oil or the metal in the engine. Could have only gotten there from the injectors. There are two ways to check this. First shut down the car for the night. Next morning, pull out all the plugs and stuff a hose down each one and sniff. You should not get a strong smell of gasoline from any of them. A trace - maybe - old injectors will be very slight leaks, but nothing strong and unmistakeable.

    The second way to check is much easier. Shut down for the night after a drive, then next morning, unscrew the holding bolts for the fuel rails and lift it up a few inches )that's the furthest they will go. Prop it against the manifold with something. Put a hose down each injector port and sniff.

    Third way is to lift up the fuel rail slightly and put a paper towel above each injector port and lightly place the rail and injector tips on it. The next morning, remove the paper towel and see where the leaks are at and how bad they are.

    After fixing this, change the oil if you are due for an oil change. If not, just run the engine at idle ro go for a short drive, and then remove the dipstick. The heat will cause all the fuel to vapourise and vent out either through the ccv during driving, or through the dipstick tube when the dipstick is removed. The oil will be thinned down a little but its not a showstopper.... it takes very little gasoline to produce a strong smell in the oil.
    I will definitely try one of these methods, just to make sure that the problem is not persisting. I think I'll go with method 3.
    Thanks for the detailed reply!

  17. #17
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    Good advice in this thread.

    What part of Los Angeles are you in? I am in Ventura and I know of a few other M5/E34 guys around.
    Current Fleet:
    E34 1991 M5 Macaoblau on Complete (ruined)Leather Champagne - http://forums.bimmerforums.com/forum....php?t=1705166

    Past:
    E34 1989 535i 5-Speed AlpineweissII on Natur - Parted
    E34 1992 525i 5-Speed Islandgrun on Pergament - Parted
    E34 1995 540i 6-Speed ShwarzII on Shwarz - Sold to Sneezy.
    E34 1995 525i 5-Speed Calypso Red on Parchment - http://forums.bimmerforums.com/forum....php?t=1748143 - Sold locally.
    E39 1998 528i 5-Speed Black on Black - Sold locally.
    E34​ 1993 M5 Alpinweiss on Black - http://forums.bimmerforums.com/forum...lpinweissII-M5 - Parted


  18. #18
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    I'm on the east side in Glendale. Maybe we should set up an E34 meet sometime.

  19. #19
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    Update: http://imgur.com/a/IsbobgN

    I changed the oil and filter and proceeded to drive the car for a week with no problems or signs of gas seeping into the oil. I switched cars and let the bimmer sit for a couple weeks. When I went back and inspected the car the oil had a strong smell of gas and the engine idled like shit. I was back at square one.

    The album above details this:
    I tried to see if I could verify the fuel leak with a really sketchy test I made up. I decided rebuilding injectors was cheap enough to try it out and got them cleaned and rebuilt. I just put them back on the car and replaced the oil. The rebuilder guy said it was very unlikely that the injectors were stuck open, as they weren't dirty enough.

  20. #20
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    Flow test results

  21. #21
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    Square one (+) it is, since your injectors are now better behaved than before.

    Oil analysis is still be your best way to assess how much gas in in your oil, and will tell you other things as well.

    One thing you could try is taking a sample of your engine oil (suck it out the dipstick tube) and in a carefully controlled environment away from the car, see if you can light it on fire. Try a sample of clean new oil as a comparison. This isn't to say that ignitable oil is bad, as it doesn't tell you how much gas might be there, but it's a qualitative test that may be illuminating for for what it does, and what it does not, tell you.

    I note that your compression test is kinda low at 130-140. Rings, pistons, or valve sealing are the suspects. A leak-down test is in order to assess ring and valve sealing. But it could also show that you need to spend real money. How bad do you want to know?
    Charlie

    Your mission, should you decide to accept it, is to add value to these threads, either by pictures or by descriptions, so the next person with the same or similar problem stands on your shoulders.

  22. #22
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    Quote Originally Posted by Honolulu View Post
    Square one (+) it is, since your injectors are now better behaved than before.

    Oil analysis is still be your best way to assess how much gas in in your oil, and will tell you other things as well.

    One thing you could try is taking a sample of your engine oil (suck it out the dipstick tube) and in a carefully controlled environment away from the car, see if you can light it on fire. Try a sample of clean new oil as a comparison. This isn't to say that ignitable oil is bad, as it doesn't tell you how much gas might be there, but it's a qualitative test that may be illuminating for for what it does, and what it does not, tell you.

    I note that your compression test is kinda low at 130-140. Rings, pistons, or valve sealing are the suspects. A leak-down test is in order to assess ring and valve sealing. But it could also show that you need to spend real money. How bad do you want to know?
    I'm about to send a sample of my oil to be analysed from my previous oil change. Hopefully that will have a conclusive outcome.

    Note that the compression test was done with a cold engine. I imagine it would be much higher if I had let the engine warm up. I think I'll run a leak down test in the future just to have that bit of information as well.

    I've been mentally preparing for the reality that I might need an engine rebuild while performing these tests. I think if it comes to that I will go for a completely different direction with this project. A much louder and more dangerous direction

  23. #23
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    Quote Originally Posted by E34M5ProjectCar View Post
    I'm about to send a sample of my oil to be analysed from my previous oil change. Hopefully that will have a conclusive outcome.

    Note that the compression test was done with a cold engine. I imagine it would be much higher if I had let the engine warm up. I think I'll run a leak down test in the future just to have that bit of information as well.

    I've been mentally preparing for the reality that I might need an engine rebuild while performing these tests. I think if it comes to that I will go for a completely different direction with this project. A much louder and more dangerous direction
    Maybe 15psi higher. Not significantly higher.

    Unless you’re in Denver... 130psi in any hole on an s38 is bad news.


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  24. #24
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    Quote Originally Posted by NikosX View Post
    Maybe 15psi higher. Not significantly higher.

    Unless you’re in Denver... 130psi in any hole on an s38 is bad news.


    Sent from my iPhone using Tapatalk
    I didn't notice any blow by when removing the oil filler cap. I know that's not a very conclusive result. I'll do a leak down test and see what's going on.
    Last edited by E34M5ProjectCar; 04-25-2019 at 10:35 AM.

  25. #25
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    an open injector killed my engine with cylinder wash, my engine had 13 quarts of oil/gas in it. when I had the problem it would just flood the engine. just replace your injectors or get them cleaned. if the oil seems thin and it smells like a 2-stroke blend you probably have an injector stuck open or leaking intermittently. hopefully you havent damaged the cylinder walls.

    edit: I see you had them checked out. did you change your fuel filter? has the car sat and if so how long? my 540 sat for a while like 7 years and even when I put my new engine in and had all 8 brand new injectors and a new filter 2 of them became clogged from all the sediment in my fuel lines. just my 2 cents. also if you do a leak down test if the rings are good even with the valves a little open you should still feel some pressure in the cylinder. I normally do it at 80psi at my job and anything within 15% is accepted.
    Last edited by 401michael; 04-25-2019 at 10:54 AM.

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