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Old 20-08-2016, 14:34   #1
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Engine dies 1 minute after start

Hello CF,

I'm having a bit of a weird issue, and I wanted to bounce it off of you guys to see if I might be missing something.

About 2 weeks ago, I fired up and after about a minute, the engine gave a little hiccup, dropping RPM just briefly, then carrying on as normal. I ran for about 8 hours with no issues.

On the next start, it ran for about a minute again, then coughed and died.

I dug into it, and discovered air in the fuel system. After bleeding, all was fine, no issues for any amount of run time.

I figure the one minute is the amount of time it takes to burn the fuel between the secondary filter and injection pump at idle, then it grabs air and dies.


This has been happening intermittently ever since. It seems that the longer the engine has been off for, the more likely I'll have a problem. I've diagnosed this as an air leak.

Just today, I did find a loose hose clamp on the return circuit, so I am hopeful that this will solve the problem. I am assuming that this loose clamp might have been enough to let some air gradually into the fuel system. The primary filters are below the level of the secondary/lift pump, etc, so I figure that this will create some suction to draw air in.

I'll give it a crank tomorrow and hopefully that's the end of it.

Any chance I'm missing something here?

Thanks, friends.

TJ
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Old 20-08-2016, 14:46   #2
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Re: Engine dies 1 minute after start

Oic. The return line goes to the bottom of the fuel tank so theres a loop... Hang on...

Waiting for an expert...
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Old 20-08-2016, 14:50   #3
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Re: Engine dies 1 minute after start

I should clarify.

The return line routes through the top of the secondary fuel filter, which is at the highest point in the system. I am guessing that small bubbles are getting in somewhere, then traveling up to the highest point.

Result- air in secondary filter, engine dies.

Thanks, TJ
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Old 20-08-2016, 15:29   #4
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Re: Engine dies 1 minute after start

Probably not important, but it's an Isuzu 70hp engine.
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Old 20-08-2016, 16:09   #5
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Re: Engine dies 1 minute after start

Check fuel tank vent . You can remove deck fill cap to prove a blocked vent.
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Old 20-08-2016, 16:12   #6
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Re: Engine dies 1 minute after start

Thanks, Deblen. We have a day tank (we filter the fuel with racors before and after this tank), and it's definitely venting correctly.

Also, once it's up and running correctly, it will run all day without issues. It's just a startup problem.

So, that's not it, but thanks for the input.

TJ
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Old 21-08-2016, 15:25   #7
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Re: Engine dies 1 minute after start

Had the same experience with a friends boat. It turned out that the particular injector pump was a rotary one. It managed its lubrication by having high volumes of fuel passing through. This was evident because the fuel return line was attached to the top of the injector pump and it was about a quarter of an inch in diameter (maybe a bit more) - much larger than the common injector return line from the injectors. (also there was no oil fill possible, implying that the pump was cooled/lubricated using excess fuel flow)
We would bleed the system and after that the engine would fire up and then die after about a minute or so. I then started the engine with the injector pump bleed nut open slightly (on the side of the injector pump). The engine started and continued to run, with fuel dribbling at the bleeder nut. Closing off the bleeder nut gave the engine about a minute or so and it would then stop.
The problem turned out to be a small rubber valve fitting inside the injector pump that was closing off and causing the internal pressure in the pump to rise. It was this higher than normal pressure that caused the problem. Confirmed by the diesel injector company that did the overhaul.
I hope this is not your problem as it is expensive to have any injector pump overhauled.
As recall, the engine was a 4 cylinder and the pump was a Bosch. I can't provide any further details as the boat is at rest on the ocean floor.
If you do not have gravity feed to the engine then the problem is either something like the above or an air entrance problem.
On another boat suffering the same symptoms above, it transpired that a small 12 VDC fuel pump used for transferring fuel and filtering had a slightly worn shaft seal letting air in when the lift pump reduced the pressure in the lines below external air pressure. The problem was rectified by attaching bypass valves around the pump as even with a new seal the problem was likely to re occur sometime. Also a day tank was installed to allow gravity feed.

Best option though is to use gravity. It always, as my body attests, wins.
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Old 21-08-2016, 15:29   #8
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Re: Engine dies 1 minute after start

Woops. Seems that my suggestion is unlikely. Particularly if the engine continues running once started.
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Old 21-08-2016, 16:22   #9
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Re: Engine dies 1 minute after start

Thanks, bilgewater. Good catch on noting that the engine runs like a champ for as long as we like once it's all bled and running.

I started it up today and it had no issues, so it's possible that I've got it sorted out, but it was only happening about one time in 5, so it'll be a few days before I really know for sure.

We'll be leaving Ireland for England tomorrow, so I'll have a good test then.

TJ
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Old 21-08-2016, 16:51   #10
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Re: Engine dies 1 minute after start

Sounds like you have a small air leak in the system, obviously at a high point that allows negative pressure. The motor dying after about one minute would happen if there was a substantial air pocket sucked through the system. Once running again the small air leak would be either absorbed by the fuel or purged through the bleed system.
If this is the problem you may be able to find the leak by pressurising the full fuel circuit and look for leaking diesel fuel.
Further proof may be gained by resourcing fuel from a higher point giving you positive pressure to the system. A plastic bottle of fuel with a length of plastic hose, pulled up the mast has solved my earlier air leak problems.
Best of luck.
Cheers
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