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Old 20-09-2010, 05:41   #1
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Engine Stalling - Open for Ideas

1980 md7a, Engine has been rebuilt, inj pump has been rebuilt, injectors rebuilt. Motor starts in 2 revolutions and runs strong. Sometimes, it seems when running the motor for a long period 2hrs + the motor will start to flucate idle +/- 500 rpm it will do this for 2-5 minutes then stall. Fuel system must be rebled from the lift pump all the wayto the injector. If I rebleed it the engine will run for 5- 10 minutes then die again. If I let the boat sit (engine cooled) and rebleed the engine will run for 2+ hours untill I have another problem. So I have to be pulling air, Im thinking about bypassing the racor to eliminate 6 feet of hoses and the filter housing and see what happens. I have already changed the fuel filters and nothing changed.
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Old 20-09-2010, 06:22   #2
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My motor would run 4 hrs then stall, it was the racor filter leaking air
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Old 20-09-2010, 06:29   #3
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RAD = racing and dying after the engine warms up usually means an air leak in the fuel supply system. Because it happens after the engine warms up the likely area for the air leak is from and including the engine lift pump to the injection pump. Examine all the pipes and connections carefully. Sometimes there are little plastic collars on the ends of the fuel pipes as they enter a filter or other part of the engine fuel system. As the engine heats up they start to leak air. Also if you have "banjo" fittings, their washers may be leaking.
- - You really have to examine each fitting carefully - very carefully - as when the engine heats starts to expand things it opens up a pathway for the air to leak in. When the engine is cool and things shrink back to normal size the air leak closes.
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Old 20-09-2010, 07:11   #4
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The engine is definitely starving for fuel--either air is being entrained in the system or you have a blockage. 1. Check the fuel tank vent by opening the deck fill after a few hours of motoring--a whoosh of air means you have a blocked vent, and that's why waiting 2 hours solves the problem. 2. Make sure that there is no strainer on the fuel pickup line in the tank. A vacuum guage on your Racor will help diagnose problems.
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Old 20-09-2010, 09:17   #5
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MD7 here too

had very similar problem (on a Yanmars though)

it was dirty fuel, in our case

engines run fine for about 2 hours, then bogged, then raced, then bogged and stopped

restarted, they worked fine for about 20 minutes, then bogged, raced, stopped ...

b.
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Old 28-09-2010, 19:10   #6
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So I flipped the racor over and let the engine run, didnt see and bubbles in the racor. So I think that rules out the line from the tank to the racor. The line from the racor to the lift pump had a section of the original hose with the banjo fitting on it and was joined by a union to my new hose . The hose was likley original and just not designed to last 30 years. So I replaced the whole hose with one new section and a plain banjo fitting eliminating the old parts. I ran it for 2.5 hrs pulling on the dock lines and it never stumbled so hopefully i got it.
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Old 29-10-2010, 18:30   #7
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Well it turns out not so much. Died in channel again the next week. So I tore into it again. I have without a doubt eliminated the problem, but I didnt fix it.
I found that there was no pressureized fuel to the fuel filter after the lift pump. I dont know that theres supposed to be, but If I pump the liftpump by hand (when bleeding) I get pressured fuel out. There is suction on the fuel filter though, Im guessing the injection pump also has a internal lift pump. I bypassed the racor and ran a line from the tank to the engine lift pump and have had no more problems. I have now run it hard for 15 + hours with no more issues. So now I wonder if my lift pump needs a rebuild Or I just need a new racor. Why does a sail boatneed a engine..............
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Old 29-10-2010, 20:53   #8
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It is not uncommon for the Racor lid seal to leak. You usually get a new one with each new filter. But some folks forget to replace the old seal with the new one. Also the center bolt/screw that holds the Racor lid in place has an O-ring that can break or leak.
- - Injection pumps normally do not have a "lift pump" or low pressure pump built into them. They will suck fuel but it is not good for the injection pump as air can get into the injection pump chambers and scour the walls for lack of lubrication.
- - You can install a "Walbro" electric diesel pump in the fuel system and see of operating with the electric fuel pump solves the problem. If it does then most likely the mechanical lift pump is defective and needs rebuilding or replacing.

- - A sailboat need an engine so you can get into and out of marinas, moorings, channels and harbors. You must stay clear of freighters and other big ships in a harbor and channel which is near impossible without an engine. And sometimes the wind is right on the bow or no wind at all, and you really need to get home/destination and you will fire up the "iron genny" to do it.
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