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  1. #1

    Default 671 engines won't fire

    Our Detroit Diesel 671 two stroke engines will not fire. We've had the boat for 4 years and the engines have been run and seemed to be working fine. Then both engines stopped within 10 minutes of each other. Here's the history:

    After installing new Walker fuelseps, port engine started, stbd engine cranks but wouldn't fire. Within 10 minutes the port engine would not go above idle and then died. Both now crank but won't fire.

    Had fuel tested, came back 310 out of 1000, a good report.

    We understood there's probably air in the system. Replaced fuel hoses. Took racors completely apart, cleaned them, installed new filters in them (even though they looked clean). Engines crank but won't fire.

    Installed an inline fuel pump, bled the fuel injectors one at a time. Engines crank but won't fire.

    Checked fuel pressure, it's running about 5 to 6 pounds.

    Any suggestions on what to do next?

  2. #2

    Default Re: 671 engines won't fire

    Can't understand why you have lost prime ... But here is how I get the air out of the system. Take your other fuel pump and hook it to the return line and turn it on .. Break the line on top of the engine mounted fuel filter ( the line that leads to the head ) when you get fuel at the fuel filter turn off pump and retighten lines you should have no problem starting it at this point. Now I would have to say from what you said you have a air leak valve closed at the tank or out of fuel going to the fuel pump on the engine a Detroit usually has around 60 lbs of pressure coming out of the pump going to the engine mounted secondary filter ( it uses the fuel to help cool the head.) There is also a restricted fitting on the head where the return line connects which slows the fuel down for cooling and maintains pressure

  3. #3

    Default Re: 671 engines won't fire

    Not sure where the air leak valve would be, and there is fuel going to the fuel pump. Thanks for the suggestion for getting air out of the system ... will be trying that

  4. #4
    Join Date
    Feb 2016
    Location
    Idaho
    Posts
    10

    Default Re: 671 engines won't fire

    Another thing that I have seen with a Detroit in the trucking applications is often they have an emergency shut off system to shut them down if they run away. And I have seem them trip sometimes for no known reason. Little unusual with two engines and right after some fuel system work but thought I would throw it out there for you.

  5. #5
    Join Date
    Nov 2009
    Location
    temecula, ca., usa
    Posts
    2,611

    Default Re: 671 engines won't fire

    You need WAY more fuel pressure! Like the man said...in excess of 40 psi. at inlet to secondary filter. Also, his suggestion about the E-STOP blower inlet door being tripped is a good one too.
    Good luck.

  6. #6
    Join Date
    May 2015
    Location
    Oregon
    Posts
    70

    Default Re: 671 engines won't fire

    A marine 671 pumps about 35 gallons of fuel an hour. Fuel constantly flows thru the injectors via fuel supply and return galleries internally in the head. Older engines have external fuel rails - works the same. To check if you have air in the system, cracking open a fuel supply or return (top of head under valve cover-connected to injector) while cranking should produce either some bubbles or solid fuel. Make sure the new Fuelseps are allowing fuel thru at the normal rate. I would take out the Fuelseps to verify fuel flows to the engines.
    The only times I have had to "bleed" a Detroit is a completely dry engine. It's self bleeding as long as there is a normal fuel supply to the engine. Usually I fill the secondary filter, make sure fuel is in the lines and fuel is at the injectors in a couple crank turns.
    If you've had very dirty diesel go thru the engine, there are small filters in each injector that look like pressed steel wool. They're normally changed only when the injector is overhauled. But if they get partially plugged not only can they effect running, but the fuel is no longer passing thru the injector in great enough volume to properly cool the tips. If the Fuelseps are reducing the flow below normal you could burn your injector tips.

  7. #7

    Default Re: 671 engines won't fire

    Thanks, all, for your suggestions. Another project came up that needs to be finished first before we can get back to the engines.

  8. #8

    Default Re: 671 engines won't fire

    Well, turns out the emergency shut-off valve on both engines was not engaged, so that's what it was! Both engines are up and running now. Thanks for all the suggestions.

  9. #9
    Join Date
    Nov 2009
    Location
    temecula, ca., usa
    Posts
    2,611

    Default Re: 671 engines won't fire

    Well. ..congratulations! But.....
    You may still want to investigate that fuel pressure reading. It could sumply be your test procedure but if you want maximum performance with the most efficient fuel burn rate....you NEED to learn about the fuel system and how to properly check it. Fuel pressure and volume is important for ANY engine and the 6-71 is one of the EASIEST to test. And you might really be happy one day that you did your homework if you get into a crappy running situatuon. Because, fuel system issues account for probably 95% of all "runability" problems on the 71.
    Just sayin'.

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