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Old 04-10-2020, 22:17   #16
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Re: Perkins loses prime overnight

Exactly where is this 'one drop per minute or two' leak? Was the engine starting and running OK with this leak previously?
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Old 04-10-2020, 23:41   #17
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Re: Perkins loses prime overnight

When I got my boat it had about 9 fuel leaks took about 18months to find them all ! One was a crack i n the return line from the injector pump that would let enough air into the pump to require bleeding . Good luck
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Old 05-10-2020, 04:52   #18
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Re: Perkins loses prime overnight

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Originally Posted by Emmalina View Post
When I got my boat it had about 9 fuel leaks took about 18months to find them all ! One was a crack i n the return line from the injector pump that would let enough air into the pump to require bleeding . Good luck
Thank you, exactly the info I was hoping to hear. When I bleed the system, it seems the air is in the injector pump - injectors themselves still have fuel at them which might explain the "runs for about 5 seconds".

18 months? Yikes! I'm hoping it doesn't take that long, but it certainly is maddening to track down.
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Old 05-10-2020, 05:04   #19
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Re: Perkins loses prime overnight

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Originally Posted by jimbunyard View Post
Exactly where is this 'one drop per minute or two' leak? Was the engine starting and running OK with this leak previously?
I can only say it is coming from the injector pump somewhere. On my Perkins, this is very difficult to get eyes on as it is underneath the exhaust manifold. I can see the bottom of it and a drop forms every once in a while while running, but obviously the drop is going to the lowest point on the pump. I have to feel with my hands and stick my phone up there and photo it to try to see what is going on. It seems to be somewhere in the vicinity of the governor, possibly from where the kill lever is but that is about as good as I can see. This is a new boat to me and it of course ran and started fine during purchase - this problem only started after I did a 22 hour delivery to bring it back home. Still runs great once bled with no hiccups or speed hunting.
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Old 05-10-2020, 05:10   #20
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Re: Perkins loses prime overnight

Really?! Fix that cant see problem first, so that you can see!
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
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Old 05-10-2020, 05:18   #21
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Re: Perkins loses prime overnight

Before messing with injector pump I would replace all crush washers and also inspect the pick-up tube in the fuel tank. A small crack will cause exactly what you are experiencing.
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Old 05-10-2020, 05:23   #22
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Re: Perkins loses prime overnight

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Originally Posted by Lazerbrains View Post
When engine is running there is evidence of a small leak in the injector pump - about one drop per minute or two. My theory is that when shut off, air comes in at the same spot and it leaks down the return into the tank. Does this make sense?
Fleshing out the story in the last paragraph of post #9... I had a small fuel leak at the discharge valve on one of the three cylinders of my injection pump (the delivery valve). Because the injection pump was above the fuel tank, it was under vacuum when the engine was shut down. Air leaked in, the injection pump could not pump air, and it was necessary to bleed the fuel system before the engine could be started. We were in the Bahamas. To get home, I cleaned the area around the leak and buried it under JB Weld which sealed off the leak. Back in North Carolina, I replaced a failed o-ring in that delivery valve. A year later, another leak appeared at a second delivery valve. I had the pump pulled, rebuilt, and reinstalled.

Your fuel leak is a fire hazard.

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Old 05-10-2020, 05:44   #23
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Re: Perkins loses prime overnight

I have the borescope that Jedi recommended... great tool. Get one.

I knew my diesel leak was somewhere on the top of the injection pump. I flushed all the diesel off the outside of the pump and the nearby high pressure fuel lines with spray brake cleaner then wrapped short pieces of pipe cleaner around the several places I suspected. After running the engine for a few minutes, I removed the pipe cleaners. The pink wet one was wrapped around the bottom of one of the delivery valves. The leak was between the delivery valve holder and the injection pump body. The shop manual had a warning about tightening the holder, thus the JB Weld.

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Old 05-10-2020, 06:01   #24
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Re: Perkins loses prime overnight

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Originally Posted by NYSail View Post
Before messing with injector pump I would replace all crush washers and also inspect the pick-up tube in the fuel tank. A small crack will cause exactly what you are experiencing.
No, it's on the pressure side. I spent the last two weeks eliminating everything on the vacuum side.
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Old 05-10-2020, 06:07   #25
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Re: Perkins loses prime overnight

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Originally Posted by wsmurdoch View Post
Fleshing out the story in the last paragraph of post #9... I had a small fuel leak at the discharge valve on one of the three cylinders of my injection pump (the delivery valve). Because the injection pump was above the fuel tank, it was under vacuum when the engine was shut down. Air leaked in, the injection pump could not pump air, and it was necessary to bleed the fuel system before the engine could be started. We were in the Bahamas. To get home, I cleaned the area around the leak and buried it under JB Weld which sealed off the leak. Back in North Carolina, I replaced a failed o-ring in that delivery valve. A year later, another leak appeared at a second delivery valve. I had the pump pulled, rebuilt, and reinstalled.
Thanks Bill - makes sense and I suspect the same is happening here and that the fuel is draining back into the return line. I am hopeful that it is something as simple as an O-ring. At this point just trying to diagnose what is happening first. Really not looking forward to dealing with the pump as I have to drain all the coolant, remove the coolant header tank and exhaust manifold just to get to the darn thing. Perkins engineers made this one reallllllly difficult to access.
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Old 05-10-2020, 06:07   #26
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Re: Perkins loses prime overnight

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Originally Posted by s/v Jedi View Post
Really?! Fix that cant see problem first, so that you can see!
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Thanks for that - definitely going to order one. I can see a thousand other uses for it on the boat besides this.
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Old 05-10-2020, 06:20   #27
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Re: Perkins loses prime overnight

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Pulling my hair out working on my Perkins 4.108.

Fairly new (to me) boat has 4.108 which started developing air in the lines. I can bleed the system and it will run fine all day, but after sitting overnight will need to be rebled again. Symptom is it starts and runs for a few seconds then dies - after bleed procedure runs fine all day. Tank is below engine. Fuel goes from pickup line to Racor, from Racor to electric fuel pump, then to lift pump, then to secondary filter, then to injector pump.

A few questions:

A) I rebuilt Racor, and it has a pressure gauge installed where the t-handle should go. Shows pressure when running and after shutting down, but next day shows no pressure - is this normal with these gauges, or should it hold the pressure here? (I also am a bit suspicious that pressure gauge is cause of air in system)

B) Could a leak in the injector pump cause this, or should I be limiting my search to the vacuum side (pre lift pump)?

Thanks so much for any advice - at my wits end trying to figure this one out. Motor runs fantastic once bled, but I cannot go on bleeding it every time I want to use it.


Sounds like a similar issue I had with our Yanmar. After getting driven crazy looking for leaks, as a last ditch effort I changed the lift pump. Problem solved.
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Old 05-10-2020, 08:16   #28
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Re: Perkins loses prime overnight

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Originally Posted by s/v Jedi View Post
Really?! Fix that cant see problem first, so that you can see!
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Or one of these endoscopes. I bought one from TMart and works right out of the box on my Android phone and Win10 Laptop. TMart webpage not responding this am, but here is one on EBay.

https://www.dinointhebox.com/product...pe-for-android
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Old 23-10-2020, 14:18   #29
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Re: Perkins loses prime overnight

So just a follow up because I hate it when I find an old thread that doesn't get to the solution.....hopefully this will help someone in the future.

Turns out that diesel was running back into the tank via the return line as a result of a leaky injector pump. The way I verified this was to put a simple inline ball valve in the return line.

So I will have to swap out injector pump with a rebuilt one, not very fun on my particular perkins as the entire exhaust manifold needs to be removed to do this.
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Old 27-10-2020, 20:18   #30
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Re: Perkins loses prime overnight

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Originally Posted by Lazerbrains View Post
Still troubleshooting this problem - takes a long time as I have to re-bleed the Perkins and wait overnight every time I make a change. At this point I have isolated each component on the vacuum side of the pump and am satisfied that all is good on that side, which leaves me to the pressure side. The problem is there is no visible leakage after sitting overnight. Is it possible that it is leaking back into the return line and down into the tank? My tank is lower than the engine, FWIW. When engine is running there is evidence of a small leak in the injector pump - about one drop per minute or two. My theory is that when shut off, air comes in at the same spot and it leaks down the return into the tank. Does this make sense? I do have a small cutoff valve on order to put in the return line which should test this theory. Again, the symptom is that after sitting overnight, when started the motor runs for 5 secs and then dies.
Where on the injector pump do you see the leak? On a high-pressure pipe leading to an injector, or at the fitting where the fuel enters the injector pump? Or is it dripping down from the general vicinity of the bottom of the injector pump? If the latter, you might suspect the fuel lift pump. I'm not familiar with the Perkins, but on a Yanmar, the lift pump is attached to the injector pump, and is operated by a small cam that pulses a rubber diaphragm inside the lift pump. If the diaphram failed, then fuel could drip out of the lift pump then run down and drip off the bottom of the injector pump. If the diaphragm leaks fuel, it would leak air -- and gets a direct run back along the supply lines. If the leak is at a high pressure pipe joint on the injector pump, I would be surprised if air could make it back through the injector pump. The little valves inside the injector pump have really, really tight gaskets and seals (to develop the necessary injection pressure). Even if you unscrewed a high pressure pipe I wouldn't think air would make it through to the fuel supply.

As I said, I am unencumbered by any knowledge of a Perkins, but it might give you some ideas.
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