Yanmar 3GM30 losing power and dying after motoring continuously

[Wrong]

Originally Posted by njb

Thanks all for the thoughts and sugestions. I need to get over to the boat to test out some of these theories....

The lift pump is original (as far as I know) but the engine was new in 2000-2001 and has about 1100 hours, seems premature for a failure? When you say the fuel should come out in strong bursts, is that from operating the manual lever, or with the engine running?

Is the lift pump replacement something I could easily do myself? I guess the interim fix (assuming that's the problem) is to just keep the fuel topped up!

Sparrowhawk: You're right I may have too many variables at play here. I will try to isolate. When the engine first died a few weeks back, It would restart but die immediately (within 30 secs). After replacing filters I was able to run the engine fine at idle for a 20-30 minutes, then ran over to the marina to have the fuel polished/tank cleaned (10 minutes of motoring). Then ran over to the fuel dock to top off the tank (another 10 minutes). This would seem to indicate that the fuel level (and thus the lift pump) are not the main culprit? Hard to say. As I mentioned, the engine ran strong for about 20-25 hours since that work was done. Then the loss of power and slow death recurred.

Possible your fuel source is selling contaminated diesel?

Do your filters show signs of this and any water in the bowl?

[SkiprJohn]

You could try isolating the tank from a fuel source by tapping in a fuel container and running your engine for a time. That would either eliminate or point out the tank or pickup tube as the problem.
Good luck in finding the culprit.

[sanibel sailor]

How about a partially kinked fuel hose starving the filter of fuel, then refilled from vacuum during rest?

[Ex-Calif]

I like the idea of the low fuel bad lift pump. carry a Jerry can and when it loses power top up and try running it...

[svrevelations]

Originally Posted by njb

Hello All,

A few weeks ago, I was out in the boat and ended up motoring continuously for a few hours (more than usual, my standard practice is to just use the motor getting in and out of the mooring field and anchoring occasionally). Shortly before getting back home, the engine started to lose power, and then died. It would restart, and then sputter and die again.

As I was overdue for a filter change, and hadn't put any fuel in the tank for over a year, I replaced both fuel filters, changed the oil, and then had the tank polished and the fuel cleaned.

Fast forward to this past week, I was out cruising and using the engine more consistently, probably put about 20-25 hrs on it over the course of the week (since the previous maintenance). After motoring continuously for a few hours yesterday, the engine again lost power, died, and then would restart but die again.

My mechanical knowledge is limited, but I found it suspect that the fuel level in the tank seemed to have been drawn down to roughly the same level during both episodes (approx 3/4-2/3 full). Given that filters and the fuel are all supposedly in working order, I am wondering if this is an air leak/vacuum issue associated with the tank??? Or the pickup in the tank?

Any thoughts or advice would be appreciated.

Thanks,
Nick

Allied Seawind 30

This sounds awfully similar to our experience! We spend a lot of money chasing down the problem - new filters, extra filters, fuel polishing, etc. In the end, we found a couple of pipes were loose and air was getting into the fuel line system. We tightened all the hose clamps and all our problems were instantly gone. I suggest you start by tightening all your fuel hose joints and you might save yourself a bit of money, frustration and time.

[Seadaddler]

Also check your hoses for leaks and maybe sucking air,sounds like a fuel related
problem.
Nick

[glynhome]

The lift pump is a mechanical lever driving a diaphragm and I had mine fail at around 10 years old. In my case it dumped 4litres of diesel into the engine sump, so I would advise that you check it over anyway.
Sadly you can't just buy the diaphragm, you have to purchase a new pump it's not difficult to fit.