Fuel Starvation?

[Pete215]

TIA for any info, I've already done a search for this problem and picked up some good tidbits on other subjects along the way.

So, problem is: After doing some maintenance yesterday (1998 Merc 5.0 with a carb), with the engine running fine, it suddenly quit. Re-started ok, ran 10 seconds, then quit. Repeat this four times.

It "felt" like the engine just ran out of gas, so I took off the newly installed fuel filter and discovered it was 1/2 to 3/4 full. Since it was brand new and the engine ran fine last week on the old filter, I swapped them, same problem. Put new filter back on, same problem.

After reading through the search results, my suspects are the fuel vent or anti-siphon valve on the tank. It's on the tank itself, right? Or maybe an obstructed or cracked fuel line? (only smelled gas when I took off the filter, not before)

Am I on the right track?

The boat is in the water, no trailer, so checking the outside vent isn't too appealing - Marina canal bottom is muck and has it's share of debris, fish hooks, etc.

I'm moderately capable on repairs, so you might have to dumb down anything too technical. :redface:

Thanks,

Pete

 

[Haut Medoc]

Re: Fuel Starvation?

Welcome to iboats.......
Do you have a mechanical or an electric fuel pump?........​

 

[Robj]

Re: Fuel Starvation?

How about a weak fuel pump? Maybe you should check the fuel pressure. If you can fill the tank OK, then probably the vent is OK. If the vent was plugged I think you would have problems filling the tank due to the back pressure.

Have a great day,

Rob.

 

[Pete215]

Re: Fuel Starvation?

Do you have a mechanical or an electric fuel pump?........[/LEFT][/QUOTE]


I'm fairly sure it's electric, mounted on the front of the engine, about midway between the filter and the carb.

I was leaning away from the fuel pump since it's downstream of the filter (I think)

On the tank vent, I haven't been to the gas dock yet, still using last year's gas (with stabilizer), not that I can even get to the gas dock right now.

Also, I checked the screen in the base of the carb, which was clean.

Thanks,

Pete

 

[Don S]

Re: Fuel Starvation?

If it's a 98 engine, it's electric. To be honest, if you can't look and tell if it's electric or mechanical, then you should probably find someone to fix it for you. But if you want to try, here goes.
The fuel pump after starting the engine is not running. That's because the oil pressure switch has either corroded terminals not making contact or the switch itself is bad.
When the engine is being started, power to the fuel pump is supplied from the starter. once it's running and the starter is no longer running, the oil pressure has built up and connects the fuel pump to power.
Here is a wiring diagram that should explain it.

 

[Pete215]

Re: Fuel Starvation?

Thanks, that seems to fit the situation.

Actually, I was 99.9% sure about the pump being electric, but since I wasn't near the boat to take a quick look, I was just hedging my bet.

I was going to take the boat into the dealer this week for something else, except I can't get it there right now. If cleaning the switch contacts works and I can keep it running long enough, I'll be happy to let them work on it. There's a local mobile mechanic, but he can be a little hard to track down.

So, at the moment, that leaves me.

So far, this still falls within my comfort zone. I'll take a look at it tomorrow.

Thanks again, it's a great feeling that total strangers took the time to help me out, gotta love the internet!

Pete

 

[Pete215]

Re: Fuel Starvation?

Update:

I checked the oil pressure switch with a test light, it had power, so I left it.
I then took a local mechanic's advice and bought a new fuel filter and pre-filled it, something I've never done before.

Problem solved - either the filter was defective, or there was air somehow trapped inside.

Boat now runs great, or did,
the sterndrive impeller went South two days ago and the "up" solenoid on the trim pump seems to be failing.

Oh well, at least they're not expensive repairs.

 

[Coors]

Re: Fuel Starvation?

You might still have a leak, sucking air, before the pump.

 

[dafar]

Re: Fuel Starvation?

I am having a similiar but not exactly the same problem. I have a 1999 mercruiser 3.0 in an 18 foot bayliner classic. I believed it was a mechanical fuel pump, but during my recent troubleshooting i verified it was pumping fine becasue we disconnected the fuel line fronm the carb and turned the motor over, lots of gas cam out.

I had some bad gas which really wreaked havok on me. I pumped the tank down transfered the gas and refilled the tank with fresh gas. In addition I added an additional feul filter(not sure that was a great idea). I also checked the in line mesh filter by the carb and it was clean.

Now the issue is different. I hvae a hard time getting the motor started, she will kick over run up and then die(as an old cold blooded truck used to do) After alot of tries I will get it running.

The motor now runs great at high speed but is dieing or running very rough at slow or idle. this is making slow speed manuvering very dangerous as I cant keep the motor running when tryin to dock.

my thoughts were these, maybe plugs? or the feul pump filter, ( a bowl that sits under the pump) or even my new filter could they be clogged from the previos water issue,,,, Help?