1995 Mercruiser 4.3

[sjm32157]

Last evening, first time in the water this season, boat is running fine. About an hour later, it starts to sputter, sounding like it is starving for fuel, will only run from just above idle to 1/4 throttle. I had a problem like this in previous years but it was the anti-siphon valve causing problems. I replaced it with a plain nipple (I know it's a safety feature but my tank is well below my motor) and all was fine. Last night, I spun off my water separator filter and replaced it with a new one. Boat runs fine but still starves for fuel when I get near full throttle (into the 4bbl). I haven't checked my fuel tank vent line or pickup screens yet but I'm starting to think that my electric fuel pump is getting 'weak'. I am pretty sure it's the original, 20 years old. I don't have a fuel pressure gauge to provide readings. Any input or ideas appreciated...

 

[hikick1]

Do mercruisers have a priming bulb? Also my fuel lines were so old (original) that they deteriorated inside from gas and clogged my filter continously. Just a thought but I suspect your fuel lines are very old and possibly deteriorating inside.

 

[sjm32157]

No fuel bulb on my boat. Fuel line is only a year old, replaced last year.

 

[tcschweitzer]

I have a 94 merc 4.3l. I had similar problems a few seasons ago. As soon as i'd get on plane the engine would sputter like it was starving for fuel and sometimes die. It died so many times one day I burnt my starter out trying to start it. I had the local marine shop tune the boat up replace all the spark plugs, fuel filters, spark wires, clean the carbs, etc. Didn't make any difference. They told me they couldn't fix it (after 2 grand in repairs) and I took it home and ripped it apart myself.

Believe it or not I was working on removing some of the seats while the engine was running. I happened to trip and fall backward and landed on the instrument panel. Guess what! the engine sputtered.

I found out the ignition wire that connects to the back of the ignition switch was loose! Every time the boat would list, vibrate or hit a wave it would short power to the engine and fuel pump causing what seemed like a fuel problem.

3 weeks in the shop and 2 grand later it was a 5 second turn of the screw to fix all the issues.

It's probably a long shot that this is your problem, but save yourself the trouble and just check it before tearing the motor apart. Get under the dash and inspect the 4 wires that connect to the ignition.

 

[sjm32157]

I will definitely look at the switch tonight and may give it a wiggle when running on the garden hose muffs. My thinking is that when that anti-siphon valve was the issue the fuel pump wasn't able to overcome the faulty valve. I removed the valve and engine ran fine. My water separator filter was due for a change and when I swapped it out the engine ran better but not 100%. I haven't checked the vent lines or pickup screen yet. Fuel pump may be tired. Years ago I fought the same issue with a car. Changed filters, added dry gas, checked spark plugs and wires, still ran rough. My Dad came home from work and tells me to pop the distributor cap and check the condenser (this was many years ago on a '68 Merc 302) It was loose, tightened and car ran great. Sometimes you can't bang your head on the wall hard enough....

 

[Bondo]

My water separator filter was due for a change and when I swapped it out the engine ran better but not 100%

Ayuh,..... Did ya check the Contents of the old filter for water, 'n crud,..??

My guess is, some of the water, 'n crud made it into the carb,.....

 

[sjm32157]

I did give the old separator a quick look and didn't see any foreign material. I put it on the muffs last night and noticed right away that half of my exhaust manifold drain plug was missing and putting a stream of water into the engine compartment. There are a couple of purple wire connections not far from where the water was splashing so I am wondering if that would have caused any problems with my electronic fuel pump. I am still going to check the vent line, pickup screen and tank but now I have to repair the manifold. The nipple in the manifold broke off immediately as I tried to get the remaining piece of the drain plug out. Ended up pulling the exhaust riser and manifold off of the boat. Now I have to find a 3/4-14 pipe tap and drill.