99 mercury efi fuel coming from oil return

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Jesse00721

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I have posted on other forums and get no responses so I thought I would give this place a shot! Here is my issue, I have a 99 merc efi 150hp that I have not messed with for a few years. Now before it smoked like you just set off a smoke grenade. Recently started looking into it again. Engine actually runs well on a stand with even compression. Not perfect. Maybe 105psi in each cylinder. Smoke is not as bad now but the oil return line (line off the bottom crank which pulsates spits out premixed gas instead of what I think should be excess oil. If I put a return tank on it it would fill up with a mixture similar to a 50:1 mix. Now, I have tried 2 different mechanical fuel pumps, 2 different ecu!a and 2 different intakes with different injectors. Pulled all reeds and have less then a .020 gap on each. My original vst had a broken float and no one had one in stock so instead of waiting 2 weeks for a new float I bought a cheap vst but it was for a 3.0 liter. Hooks up the same, only real difference was the high pressure fuel pump was mounted in the tank instead of on the outside. Does not matter but no matter what is changed I can't seem to stop fuel coming out of the oil return. Does anyone have any idea what the issue might be? Thanks, Jesse
 
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Re: 99 mercury efi fuel coming from oil return

Hi there, Just throwing it out there but there is a 2 psi check valve that prevents gasoline from being forced into the oil lines. If the check valve is inoperable then it seems that oil and fuel could mix.

In the first link below, On page 3E-2 (#20) describes the situation. Page 3E-3 shows a diagram of where the check valve should be.

http://1manual.com/Mercury manuals/Service Manual PDFs/TwoStroke/824052r3/3e.pdf

Looking at a parts diagram, the only check valve I see at the moment is mercury part number 21-424811 item number 11 in the next link below.

http://www.mercruiserparts.com/Show...br=3743&bnbr=120&bdesc=FUEL+MANAGEMENT+SYSTEM

21-424811 CHECK VALVE, Oil Injection

This is just a guess, So good luck.:)

Also you need to ensure that the fuel pressure and regulator are the same specifications between the two VST tanks.
 
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Jesse00721

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Re: 99 mercury efi fuel coming from oil return

I can check the pressure but they do the same thing. I have looked at the first link many times but my issue is that appears to be carbs. So that check valve is not there. The fuel flow goes to the mechanical fuel pump, over to the fuel/ water separated then back to the top of the vst so no oil is being mixed there. The other valve on the parts diagram pumps oil directly into the bottom of the vst from the oil pump and mixes gas in the vst there. So if to much oil pumped in the bottom of the vst I could see an over mixture but neither seem to cause gas from the oil return line to me anyhow. Like there is too much gas in the crank instead of excess oil pulsating out. Thanks
 
Dukedog

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Re: 99 mercury efi fuel coming from oil return

Jesse00721 said:
Smoke is not as bad now but the oil return line (line off the bottom crank which pulsates spits out premixed gas instead of what I think should be excess oil. If I put a return tank on it it would fill up with a mixture similar to a 50:1 mix. Jesse
Click to expand...

You reference this "line" twice. Exactly which line is it? Where is connected on "both" ends? Is it tha one goin' from top ta bottom of tha block at tha crank bearings? Is that what ya mean when ya say "crank"?
 
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Re: 99 mercury efi fuel coming from oil return

That's a pressure "supply" for tha main tank in tha boat. Its a "one way" fitting. They're shouldn't be nothin' but air being discharged on tha pulse. Does your main tank (in tha boat) seem ta be "makin'" oil lately?.......
 
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Jesse00721

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Re: 99 mercury efi fuel coming from oil return

Yeah I thought excess oil would flow there, but instead it's a premixed gas intead of nothing but air. No external tank hooked up since I have it on a stand. I would not think one would need to be hooked up to prevent anything from air pulsating out of there, of course I had to pull the lower today to put on another engine so I'm short the lower unit now, about to remove the entire system and bypass the oil injection and make it premix only or put carbs on but I would hate to make an efi a carb engine. Guess it depends on how much longer I can't figure out the issue before a new approach is taken. Just can't figure out the oil gas mixture coming out there if it is just supposed to be air?
 
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Jesse00721

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Re: 99 mercury efi fuel coming from oil return

By the way, if oil ang gas mixture is there and you bypass it, where is that suppose to go, just burn off? Shouldn't there be some oil to lube the engine anyhow? Does it get exhausted out or will it slowly just fill the crank? Can't get the bypass concept of the excess.
 
Dukedog

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Re: 99 mercury efi fuel coming from oil return

Replace tha valve and rebuild tha mech. fuel pump if ya leave tha oiler intact. If ya dump tha oiler just rebuild tha mech. fuel pump..................
 
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Jesse00721

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Re: 99 mercury efi fuel coming from oil return

By the valve do u mean the one I referenced in post number 5? I can do the fuel pump. I got 4 of them but just could order a rebuild for one.

Thanks,
Jesse
 
Dukedog

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Re: 99 mercury efi fuel coming from oil return

Yessir. Are ya gettin' a suction and a discharge from tha valve? Pump kit is just a precaution. May/may not be a problem but an easy fix just in case...Kinda difficult doin' this on a computer! If ya do away with tha oiler be sure and add oil to tha existin' tank at 40/50 (your choice) ta one then run motor a tad "before" ya disconnect tha oiler........
 
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Jesse00721

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Re: 99 mercury efi fuel coming from oil return

Just an update, yes many air come out there, after checking a few other engines some gas mixture also vents out so I now believe this to be normal operation. Thanks for all the input.
 
Dukedog

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Re: 99 mercury efi fuel coming from oil return

So your sayin' your gettin' a pre-mix being injected ita tha main oil tank???
 
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Jesse00721

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Re: 99 mercury efi fuel coming from oil return

I don't have a oil tank hooked up. If you put your hand over the 4 psi check valve that pulses you get a little mist on your hand if you leave it there, checked 3 engines and the all do the same thing. Not shooting out but it does feel like a gas residue if you hold your hand there long enough.
 
Dukedog

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Re: 99 mercury efi fuel coming from oil return

Gottcha! I was picturin' a lot more, like a "squirt".....................
 
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