fuel line mystery

[DCoulter]

Well it happened once more, the volvo engine in my 1982 CD-28 passed out again, perhaps the sixth or seventh time in two seasons. Comfortably motoring at 2200 rpm and 20-25 minutes later it just loses power and conks out. Then in about 4-5 hours ready to run again for another brief stretch. The fuel tank has been cleaned and polished, new filters installed, fuel only 6 months old with enzyme cleaner, new fuel pump, fuel pick up tube in tank ok, fuel lines vacuum/pressure checked out ok. Noticed last weekend a bit of diesel film on copper injector tubes, and I have not checked the fuel tank air expansion lines. Problem does not seem to happen if engine is just running out of gear at dock. The engine does give me a brief hesitation before it dies and I feel as though I must give it more throttle to bring it up to 2200 - 2500 rpms. I suspect some heat related problem so I wonder about the injectors. This becoming a regular occurence so I would sure appreciate any Sherlock Holmes sailors out there to help me with this frustrating mystery. Thanks, David

[Oswego John]

Hi David,

I have no clue at this time what causes your problem. The first thing that came to mind, and its a real shot in the dark, is I wonder if you have a vented cap on the fuel tank.

The premise is that as you consume fuel, air has to replace that fuel otherwise you will create a vacuum in the fuel tank. This will prevent or restrict fuel flow to the engine.

Just a wild and crazy guess. Maybe crack the cap open a bit and see what happens. I hope it is something simple.

O J

[Warren S]

I'm not sure how the 28's are configured, but the 270 uses a watertight (and therefore airtight) o-ring-sealed deckplate. None the less, I'll go with OJ to check the vent hose and transom (on the 270 anyway) fitting to make sure there isn't a mud-wasp living in there.

Another thought: does it do this regardless of the amount of fuel in the tank? We have found that on port tack, the sump will begin drawing air in choppy seas (right when you need the engine the most) and quit, with not to much as a pop on restart attempts. Tack the boat, and she starts right up. This is a long shot, as I think the 28 fuel tanks are located elsewhere then the 270, which is amidships.

[river-rat]

If you don't have one, suggest you install a vacuum gage between the fuel pump and the fuel filter. This can be very helpful if finding a clogged filter or other impediment to fuel flow. Some filters have a port for connecting a gage. If a clogged vent to the fuel tank is responsible the gage may show a slowly decreasing vacuum before the engine will fire again.

Used gages may be available at low cost.

There are several other possibilities including air in the fuel system and a malfunctioning injector pump. Injector pumps are very expensive so be sure that is the problem before buying a new one.

[tartansailor]

Once heard if a fuel line installation where the replacement line was
placed too close to the exhaust; the result being a vapor lock.

Dick

[Jim Davis]

Happened to a friend, one of his fuel hoses broke down internally, from the outside it looked good.

[Ron Brassord]

It would seem the cause of the stall is air intrusion somewhere in the fuel delivery system? An easy check is to install a short piece of cleay tubing between the injection pump and the fuel pump. This will show the smallest amout of air from anywhere in the line, and it doesn't take much.
Another possibility is an issue with the fuel filter that once drove us nuts. If you have a convential domed filter like a Racor ,a pocket of air can collect in the top and when the boat heels, the slug of air is enough to kill the small enging, requiring bleeding. I learned this from talking with Raco. They sent us a filter [free] with an exit port on top of the lid and solved the problem. I think tilting the filter so the side exit port is higher than the intake would do the same. It would be worth a try to see if that is your proble.
Good luck Ron B

[Steve Laume]

The easy and cheap stuff first is always my mode of trouble shooting. Not changing everything at once is also key to actually finding out what the problem was even if you do solve it.

With a vacuum gauge you could rule out quite a number of possible problems. This would not be a solution to your problem but would always provide very valuable information as to the current state of you fuel delivery system. For the relatively low cost and ease of installation it seems that no diesel powered boat should be without one of these gauges.

As to actually solving your problem several people have suggested the vent system as a possibility. Before you start poking around too much, simply removing the hose from the tank and blowing through it would tell you everything. Free flow and you should be good.

That would be really easy then move on to low pressure fuel delivery.

I am in the plugged vent camp, Steve.