Hey guys, now does this motor have 2 seperate fuel pressure regulators? One in the cool fuel box and also one on the back of the Intake pendum. 2 hoses come off of the intake which are connected to a 90 degree elbow. One hose goes to the cool fuel, and the other curls around and goes to what appears to another fuel pressure regulator which looks like it is bolted to the pendum

I performed my fuel pressure test tonight, with the fuel psi only topping out around 18-20 on the gauge with the motor running. the motor only ran for about 30 seconds and stalled, with us not being able to get it to fire again. the pressure readings were Exactly the opposite as everyone has been saying if it were the regulators. I've been told that normal psi with the motor running at idle is 38-42. With these findings I would have to make a guess that the mechanical fuel pump is still operating, pumping around that 18-20 range, and the elctric (boost) fuel pump isn't working at all. Tomorrow I might see if I can actually disconnect the wiring to the electric fuel pump and crank the motor and see what the psi on the guage will read. Any thoughts?

Wow, well that explains why you're running like crap, you have to have 40 psi. The thing that looks like a regulator on the plenum is called a fuel damper, and does not regulate the overall pressure. The pressure regulator is in the cool fuel box and has likely failed. You will not get 18-20 from the mechanical fuel pump so either the electric pump is weak or the regulator is stuck wide open. I didn't pay enough attention to your first post, the backfiring is almost always due to lean condition. Now that I think about it the electric pump could be running weak because the mechanical pump has failed. Do you by any chance have fuel in that hose that runs between the mechanical pump and the intake?

Ted, thanks for the response. Tomorrow I will check the hose you are talking about for fuel between the mechanical pump and the intake. My theory after tonight's readings on the pressure gauge is that the injectors are not spraying fuel like they should, but more like a light drip, therefore the air, fuel mixture is not burning due to the lack of proper fuel pressure and that explains why you can smell raw fuel. I might also add, before I started the boat tonight, I did pull a spark plug and could easily smell raw fuel on the plug.

Now to go with what you are saying: Another fuel psi reading I noticed before I even started the boat was around 10 on the gauge with the key turned on, therefore the electric fuel pump was building a pressure before the motor was running? Now that might mean the electric fuel pump is actually working? And with the motor running, the mechanical pump may not be working at all with the electric actually building the total 18-20 psi I saw? If the pressure is supposed to be around 40 under normal operating conditions that it make sense one of those pumps are not working since I'm getting half I should have. And it makes sense that it could be the mechanical pump because I do build some pressure with the key turned on. Also, is there another to test the pressure regulator alone, that way I can narrow the search down a little farther?

A 500EFI has a mechanical fuel pump??? Just a thought but couldn't a faulty injector that is stuck open be dumping fuel into a cylinder and causing low fuel pressure? That would explain why it runs better at higher rpm and the smell of fuel at lower rpm.

To check the regulator remove the hose from the regulator to the fuel filter canister (#30 in the illustration below). Now plug it off, cycle the key on a couple of times (don't crank the engine) and see if the pressure goes up (be careful, there can be a lot of pressure there), if it raises up over your 20 psi then the regulator is bad. You could also remove the feed line from the mechanical pump (#50), put it in a jar or can and crank the engine, that would show how much it is pumping, if at all.

http://www.mercruiserparts.com/Show_...nd+Fuel+Cooler

The electric fuel pumps don't suck well, so they feed it with a mechanical pump. If an injector was stuck you wouldn't lose that much pressure, they have really really small openings. Although we have been seeing lots more sticky injectors because of the ethanol, so they could have issues too. Mine were checked and cleaned 2 years ago but I will do them again this winter.

Got ya. I just thought it was odd that he has low fuel pressure but could smell fuel.

Interesting on the fuel pumps as mine only has an electric pump.

What did you come up with? I am having the same issues. I've changed plugs, wires, cap, rotor, fuel pump, filters and regulator and still having issues. Boat is a 36 Outlaw

I'm actually having the same issues! No codes showing. Plugs are wet and smell of fuel, loads up and stumbles when idling through No Wake and spits and sputters until on plane then it cleans out. Have checked all of the above mentioned and fuel pressure is about 40# at idle at the rail. I DID however make the mistake of putting 93 octane fuel in it and am being told that that may be my issue. 500efi isnt built and tuned to run premium and isnt burning all of the fuel and therefore loading up. Hopefully that is my issue.