Pressure reg/Vapor separator

[Diamond Dave]

I have a 1995 Merc150 E.F.I. Black max XRi The motor was sitting for about a year after the magnets came apart on the flywheel and tore up the stator. I?ve replaced the flywheel and the stator the motor starts now but, it?s pissing fuel out of what appears to be a vent hole in a little brass fitting that a vacuum hose goes to that comes off the fuel pressure regulator. Motor is defiantly running rich. HELP! I?m thinking the fuel pressure reg is bad. What?s the deal with this vapor separator that the pressure regulator is mounted to??? Does it have anything to do with the function of the reg??? THANKS

 

[jimc_LA]

Re: Pressure reg/Vapor separator

Dave, I had a similar issue about a month ago while rebuilding the fuel system on my '00 200 EFI. I had changed the high pressure fuel pump and filter and cleaned out the VST, replaced fuel hoses. Pumped the ball up and discovered fuel leaking from the same fitting you reference. No one on this forum chimed in because I don't think this is a very common occurrence, certainly isolated to fuel injected models.

After working my way through the rest of the fuel delivery system, what I finally discovered was as follows:

If you follow the (2) fuel hoses (supply and return to/from the fuel rail to the VST) to a double fitting at the fuel rail housing, remove this fitting via the (2) phillips head screws. You are going to see the ends of (2) aluminum tubes that "bridge" the gap from this fitting to the end of the fuel rail. there are o-rings at each end of each of these tubes. In my case there was a split in one of these o-rings. They are an odd size and I had to go on-line and order some from an o-ring mfr.

If you look at this area, the only way for fuel to come out of that vent hole in the fitting is if the space where these tubes run gets fuel into it. From what I could tell, the only way that could happen is if these o-rings were leaking. Turns out they were and after replacing it fixed my problem.

By the way, I pulled these tubes out using needle-nosed pliers and twisting/pulling at the same time. It was fairly difficult to get them back onto the holes in the fuel rail as you have limited space to work in. I ended up coating the o-rings with lube and using a wood dowel while tapping with a small hammer. They eventually seated, but I was worried that I was going to cut them while installing. Could be that the proper way to install them would be to remove the fuel rail assembly and install outside of the housing, not really sure. If mine ever leak again, this is what I will de when I replace them.
The outer end seems to slide over the brass fitting fairly easilybecause it has a good taper to it.

Although this is a different engine, it sounds exactly like what I was faced with. Let me know if you have any questions.

Good Luck.

Jim C.

 

[Diamond Dave]

Re: Pressure reg/Vapor separator

Jim,

Thanks, I can?t begin to tell you how much I appreciate the help. I'll let you know what I find. Thanks again.

Dave

 

[jimc_LA]

Re: Pressure reg/Vapor separator

Dave,

I doubt that there is anything wrong with the fuel pressure regulator. I initially thought that mine might be bad and ordered another ($100). In fact it just came today. In the meantime, I have run it and everything is fine with the fuel system and fuel delivery. I may change it out anyway.

VST (vapor separator tank) acts as a holding reservois for the high pressure fuel pump. Your oil pump actually injects oil iinto the VST so that it is pre-mixed with fuel prior to being sent through the fuel rail to serve the injectors by the high pressure fuel pump. The low pressure (pulse) fuel pump keeps the reservois filled and there is a float with needle valve in there. You should hear the high pressure fuel pump come on when you first turn the key to the "on" position (not start). It'll run for about 15 seconds or so and shut off. High pressure pump should put out about 32-34 psi. Fuel pumps into the fuel rail throuogh one of the two tubes previously mentioned and whatever is not needed by the injectors comes back through the second tube, through the pressure regulator, to the reservois. It's like a small closed high pressure loop. There is a discharge valve (looks like a tire valve) adjacent to the presure regulator for discharging the system. Beware, if you need to open the VST, there is an o-ring gasket that is not going to be re-usable and you'll need a new one (about $30) as the old one stretches too much to re-fit it into the groove on the tank. If you have fuel delivery issues (bogging when you try to throttle up) and your high pressure pump is working, it may be that the filter at the bottom of thhe pump is varnished up and clogged (it has a very fine mesh screen). You can clean this with a degreaser and re-use it if you are careful. It removes with a clockwise twist of about 15 degrees then pulls off. If your high pressure pump is not coming on, it could be gummed up. I've heard that they can sometimes be made to work again by soaking them in Seafoam or Berriman's B12, but I didn't try. A new one will cost you $400-450 at an aftermarket outlet or $600+ through Mercury. Comes as a kit with a new filter and carious o-rings.

If all you are experiencing is the leakage through the vent fitting, it's most likely just the o-rings because that part of the system is under pressure from both squeezing the ball and from the pump once the key is turned on. Pull the hose fitting off as I described and pull the fuel tubes out and inspect the o-rings. If you need to order them, go to an aftermarket o-ring supply house. You'll need to measure them (ID and thickness). I bought extras ( they're about .25 each). If you go to Mercury, they're not available separately, only as part of a kit that costs aboout $250.

Let me know if you have any other issues regarding the VST. I just finished dealing with mine a few weeks ago and know this part of my engine fairly well.

Jim C.