2000 4.3 Mercruiser starts but won't stay running

[maverick7687]

There seem to be a lot of these threads around lately.

Engine S/N: 0L658058
Thunderbold V Ignition
Don't remember the S/N of the carb but it is the factory 2brl with the Accel pump that has the 90 degree hook at the top and no check ball underneath.

I'm really wanting to bounce around some ideas and get some suggestions on what to check next.

I recently acquired this boat (2000 Bryant 196) and I am trying to get it waterworthy. It was stored outdoors with a slightly leaky cover and there was water in the engine bay when I picked it up.
I couldn't get it to start up so I replaced the spark plugs and the sensor inside the distributor. That did the trick. It will now start and run, it starts a little hard and will not stay running long (Average is 1 minute, sometimes 30ish seconds) then it dies like it's running out of fuel. Figured that should be easy, check flow to carb, maybe rebuild carb, done... Nope

Things that have been done already:
- New plugs
- Dist. cap/rotor
- Dist. sensor
- Verify fuel pump operation
- Rebuilt carb.
- New fuel/water filter


I had the carb apart twice, second time someone suggested recleaning the venturi section to no avail.
There was one time I swapped hoses from the boat tank to a portable fuel tank and let it run, it did the same thing a few times then ran for 5-10 minutes. Swapped back to the boat tank, ran for 2-3min and sputtered out again. Tried a few times with same symptoms as before. Swapped back to the fresh gas can and it wouldn't stay running like before. Could possibly need more time to run contaminated fuel out of the filter and get all fresh in but I thought I gave it enough time.

My next step is to keep trying the fresh can and connect a meter to the fuel pump wires to make sure it's keeping voltage (maybe oil pressure sensor intermittently cutting the pump?).
Pump seems nice and strong to me. Connected 12v to the pump alone and dropped a hose in a tank and pumped 5gal in about 7 minutes. Should be plenty to keep the carb fed, but I am a FI guy, never dealt with carbs.

It got too late and I couldn't keep starting it (live in the city, unfortunately, close neighbors) so I figured I would call it a night an do a little more research.

Any useful ideas from the experts?

EDIT: When engine starts to stumble out, pumping the throttle (I'm assuming because the Accel pump pours gas in) will make it pick back up and run for a short time.

 

[Fun Times]

Things that have been done already:
- New fuel/water filter

Did you install the new filter "before" any of the actual fuel system testing or after finally getting the engine to start and run with new sensor/plugs, etc. ??
What brand/part number filter did you buy and are you 100% sure the new filter wasn't accidently installed with the old filter O-ring still stuck to the upper filter housing assembly so that there might possibly be two O-rings in place? Also bear in mind that sometimes even new filters are defective.

There was one time I swapped hoses from the boat tank to a portable fuel tank and let it run, it did the same thing a few times then ran for 5-10 minutes. Swapped back to the boat tank, ran for 2-3min and sputtered out again. Tried a few times with same symptoms as before. Swapped back to the fresh gas can and it wouldn't stay running like before.

Thinking the filter is/became more on the empty side making the pump work harder. Until you get this figured out, For testing purposes, If you manually prefill the filter, it should help the engine start easier. Then if the engine seems to run out of fuel again, check the level of the fuel filter.

So it sounds like a possible problem on the boat side such as the fuel tank anti siphon valve (http://www.bakesonline.com/images/malantsiph_LG.jpg ) is gummed up or the plastic pick-up tube inside the tank may be cracked sucking air, the filter type screen at the bottom of the pick-up tube is covered in debris or the boat fuel line between the tank and engine filter assembly is internally disintegrating enough to cause splinters impeding fuel flow.

My next step is to keep trying the fresh can and connect a meter to the fuel pump wires to make sure it's keeping voltage (maybe oil pressure sensor intermittently cutting the pump?).

Yes you need to ensure you are not losing 12v to the pump as the oil PSI switch could very well be intermittent by way of lose/corroded electrical wires or internally failing.

Pump seems nice and strong to me. Connected 12v to the pump alone and dropped a hose in a tank and pumped 5gal in about 7 minutes. Should be plenty to keep the carb fed, but I am a FI guy, never dealt with carbs.

That flow rate seems good. If needed, try bypassing the oil switch with direct 12v to see if it stays running on both portable and boat fuel tanks.

EDIT: When engine starts to stumble out, pumping the throttle (I'm assuming because the Accel pump pours gas in) will make it pick back up and run for a short time.

Maybe because with a low level fuel filter, the pump is just struggling to get any amount of fuel it can to the carb.

Also you'll want to inspect your fuel pump thoroughly since your engine serial number falls just within this older mercruiser service bulletin -Stainless Steel Electric Fuel Pumps

And here is some helpful tips about fuel pumps, Electric Fuel Pump Troubleshooting - Marine Mechanic

 

[maverick7687]

Thank you for the suggestions. I hooked a meter to the fuel pump wires and fired her up. 12-13v, awesome. Turned the key off, turned it back on (Key on Engine off) 12v back to fuel pump with engine not running and oil pressure alarm sounding. Fired right back up and ran for 20-30min.

Conclusion: I am almost positive that the oil pressure sensor is bad, it was intermittently fals stopping and now it is sticking closed and keeping the fuel pump running 100% of the time.