[mariah1stnow]

I have a 96 Mariah Shabah 180 and I have issues with the boat running in the water. It starts fine on the trailer but then it dies shortly after being unloaded. I disconnected the fuel line before the carbs and there was absolutely no gas spitting out when I tried to start it. Do you think this is an issue with fuel pump or the electrical system and what can I do to fix it?

[WetWilly]

Hi mariah1stnow,

Well to start off with, it would help to know which power plant we're dealing with because Mariahs came with a 3.0L and a 4.3L SO to help our members get you the correct information when you post, please add the year, model, motor size and outdrive type of your Mariah to your user id. This will explain how by clicking here.

Ok, that said, being the fuel pump can depend on whether you have a mechanical or electric fuel pump (since you said carbs, I assume mechanical but just checking). If it's mechanical, it should pump whenever the motor is cranking, there is also a clear tube from the pump to the carb, if there is fuel in this tube, pump's diaphragm is gone, time to replace pump. If electrical, then there is a few things involved. BTW, when did you last change your fuel filter?

WetWilly

[mariah1stnow]

Sorry, I was in the middle of looking at the boat and left out some details. It's the 4.3LX Gen+ with the aplha one. The boat has an electric fuel pump which I can never hear kick on. I am ordering a new fuel filter for it today.

[WetWilly]

Hey mariah1stnow, that's better, now we know what we dealing with so let's see about getting you back on the water pronto!

If the fuel filter doesn't fix the issue, here are some other things to look at:

1) Check your motor's oil level. The manual shows there is an oil pressure safety switch in line with the pump's power and I believe it’s designed to shut off the pump if there is a drop in oil pressure.

2) Check the oil pressure safety switch. It looks like the power comes from the alternator then to the oil pressure switch and then branches to the pump and the starter. I think the switch is normally open when the motor is off so testing it will be difficult until the motor fires up and establishes some oil pressure. I believe that when you first start your motor, it's running off of the fuel in the carb, once the oil pressure rises enough, the oil switch closes, the pump turn on and the motor continues to run.

3) Check the pump. If you want to test just the pump, carefully jump the Pur/Yel wire on the pump straight to the positive on the battery, you should feel or hear it run. Of course the safest way would be to remove it from your Mariah before testing!

4) Check the wiring and connectors for any sigh of corrosion, clean as necessary.

Good luck and be careful,
WetWilly

[mariah1stnow]

Thanks for the info. I will check on it and let you know the results.

[lakelizard]

I have a '92 MX19 with the 4.3LX (175 h.p., 2-bbl carb), and had the same problem. In '92 and early '93, Merc installed an inline canister filter, which is no longer available through Merc. I purchased the conversion kit to swap it over to the spin-on filter, and was able to measure 5.5 pounds of fuel pressure, pulling through the new filter. The next day, when I got the boat out to run it, no go. I pulled the line loose at the carb, and no fuel. I disconnected the line from the tank, installed a fitting into the filter housing, and dropped a line into a gas can. It started right up. So, I disassembled the fittings at the tank, and there's a ball-and-spring check valve in the fitting on the tank, that the 3/8" line hooks to. It wasn't operating properly. After a little online research, I ended up removing the ball and spring, and reassembled the fittings and lines. Now, it runs just fine. From what I could tell from my research, most people were either removing the check valve, or just replacing the fitting. In addition to not starting/running, there were also complaints about a lean fuel situation burning pistons and such. Don't know if this will help, but you might check the fitting on the tank.

[lakelizard]

By the way, Wet Willy is right. The electric pump is not activated until the engine is actually being turned over. It does not kick on with the key being turned to power up the other systems. The oil pressure switch has to measure at least 4 lbs. of oil pressure to complete the circuit, and activate the pump. After that, if the switch fails to measure pressure, it will cut off power to the fuel pump. You can pull the two wires off of that pressure switch, and jump them to temporarily complete the circuit, to test the pump. The switch is located just above the oil filter.

[WetWilly]

Thanks lakelizard, it's great when a member with the same I/O setup can chime in and identify where everything is located!

WetWilly

[mariah1stnow]

Thanks lakelizard. Are you talking about the anit-siphon valve or something in the 90 degree elbow?

Ok, so I changed the fuel filter and it was full of clean gasoline. I still put a new filter on. It looks as if I am getting fuel to the filter but not up to the carbs.

I actually ran a line straight from the battery to the fuel pump. The fuel pump would kick on sometimes and sometimes it wouldn't. Does the pump have a feature which turns it off if I supply direct power too long?

I guess the next step would be to check the oil pressure switch by jumping the wires.

Thanks!

[lakelizard]

Yes, that's the fitting I was talking about. What I found with mine is that there was some corrosion inside of the fitting, and the check valve wasn't operating properly. According to the information I found online, this check valve was something that the government wanted installed, to prevent fuel from escaping the tank in the event that the boat capsized. I don't know if that's exactly right or not, but I figure if your boat is capsized, you've got bigger problems to deal with than that.

As far as the pump goes, there's nothing I'm aware of that would cause the pump to operate intermittently, except failure. The one thing I was warned about is running the pump for any length of time at all, if there was no fuel getting to it. That could cause pump failure pretty quickly, so I was told. Like I said, I was able to measure 5.5 pounds of pressure at the pump outlet, drawing fuel through the filter. According to the good book, you should have between 3 and 7 pounds on a carburated engine. Your problem sounds like an issue with the pump, if you had gas in the filter. There was no fuel in the lines or filter when I took mine apart.