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Old 10-03-2011, 07:35   #1
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Hard Starting 4-108

Air is getting in somehow I believe, causing impossibly hard starting every time now . I recently had the injector pump rebuilt owing to fuel leaking and hard starting. This fixed both problems for a few months. However the hard starting problem has returned. Where should I look now? Should I replace the entire suction side of the fuel delivery system? Is there a way to detect where a suction leak is coming from. The engine has 1000 hours on it.
Lots of wd-40 and starter fluid seems to be the only way I can get it to start, it always runs great when it finally starts. I don't want to damage the engine though!!
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Old 10-03-2011, 07:56   #2
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Re: Hard starting 4-108

Have you looked at the air intake?
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Old 10-03-2011, 08:08   #3
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Re: Hard starting 4-108

What do you mean? Isn't that where air is suppose to get in from anyway?
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Old 10-03-2011, 08:11   #4
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Re: Hard starting 4-108

There are two things that make diesels run. Fuel and compression. Check your compression to make sure your rings are ok. If compression not the cause I would check around the fuel filters as they leak air if not tightened or installed properly.
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Old 10-03-2011, 08:19   #5
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Re: Hard starting 4-108

The compression is good, it's definetly air in the diesel. Most of the 700 hours that I have put on the engine have been trouble free "instant" firing up!
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Old 10-03-2011, 08:27   #6
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Re: Hard starting 4-108

Great. My engine used to fire right up till I serviced the fuel filter. Now after setting for a week due to air leak it has to prime all over again. Try to avoid the starting fluid though. My previous engine was hard to start also and turned out to be valves in head. But if that were your problem it would show up in compression test. Hope this helps. Look for easy things first.
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Old 10-03-2011, 08:33   #7
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Re: Hard starting 4-108

Is any part of supply/return tubing transparent? (easy to check for air bubbles)
Are both supply/return line ends submerged in fuel inside tank?
Is fuel filter mounted? If yes, has it been changed recently? Does it seal well?
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Old 10-03-2011, 09:28   #8
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Re: Hard Starting 4-108

The tubing is mostly steel and partly black rubber so no chance of seeing bubbles. The fuel filter is mounted and changed 120 hours ago. I will check all connections thoroughly. Is the fuel suction side the only area where air could enter the fuel? This would conciderably narrow down the area of search. Thanks for advise!!
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Old 10-03-2011, 13:38   #9
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Re: Hard Starting 4-108

Ok so I just changed all fuel supply lines on the suction side ,and I tightened some loose connectors. It appears to be starting well now ,BUT TIME WILL TELL if its a small air leak! Just one point, as I was loosening the injector fuel lines (with engine running 1500 revs) one of the 4 unions was jetting out a little bubbley fuel at base of union along with the powerfull squirting diesel. Is this normal? Should I leave the union cracked open a little untill all the bubbles go? will it correct itself by itself?
Of course the revs dip down as I loosen each union in turn (quite normal)
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Old 10-03-2011, 13:55   #10
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Re: Hard Starting 4-108

Normal procedure when eg. replacing injectors is to loosen the injector fuel line union one by one while cranking, to flush any air out (helps too with flushing out any tiny debris which might have loosened itself from threaded areas). Have some clean cloth handy to catch/clean the spill.

Air in high pressure fuel lines will create great problems with starting and may prevent starting completely. There should be no bubbles (nor diesel leaks) around properly tightened unions. With tanks located below engine (normal case) _any_ air leak will cause fuel to return to tank and fill fuel lines with air. Make sure there are no leaks on either side.

Personally, when I have to disconnect any fuel hose I wet the mating areas with a very thin film of grease before reassembly. Just a wetting, nothing more. I use silicone dielectric grease for this purpose to avoid damaging any rubber. Probably an overkill, as the rubber in question is fuel/oil resistant, but it served me well for years, so why change?
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Old 10-03-2011, 14:21   #11
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Re: Hard Starting 4-108

Yes, leave the union cracked open a bit until all the bubbles are gone. It may correct itself or it may cause problems if you don't remove all the air in the lines. I used to bleed the Perkins at the injector end of the fuel line and made certain each had no air bubbles.
Glad you found the solution. It usually is something on the suction side of the fuel supply that causes these situations.
kind regards,
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