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Old 17-04-2011, 18:40   #1
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Perkins 4108 Fuel Problem

Greetings
I have a 4108 Perkins that is giving me some problems with the fuel system.
Starting from the tank I have a 30 micron screw on racor filter, a vacuum guage, an electric fuel pump and then the lift pump on the engine followed by the 2 micron engine filter. This has worked well for about 3 years. Now the engine stopped running as if the filter had clogged but the vacuum guage did not show any suction. I replaced all filters and bled the engine then it started fine. It ran for about 20 mins then died again. I rebled it but same problem. I tried bypassing the racor and the electric fuel pump and the engine ran for about 50 mins before reving up and dying. The fuel is clean and the pick up is not clogged.
I suspect the lift pump may be leaking into the engine oil as the oil level seems to be 2'' higher than I remember.
Does this make sense and am I on the right track?
Many thaks for any advise
Mark
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Old 17-04-2011, 18:44   #2
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Re: Perkins 4108 fuel problem

Do you run the electric fuel pump while the engine is running?

If that is the case, the diaphragm in the fuel lift pump is compromised and you are pumping the fuel into the engine.
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Old 17-04-2011, 18:48   #3
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Re: Perkins 4108 fuel problem

You could also have a leak in the fuel line or pickup tube that is allowing air into the system as well as the lift pump.
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Old 17-04-2011, 18:57   #4
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Re: Perkins 4108 fuel problem

Check all connections on suction side....if you have "olives" (compression fittings with a rubber o-ring....replace the o-rings.

What is occuring is small air bubbles getting into the fuel system.....the return line goes to the secondary filter and eventually fills with air.

Since the engine ran at length....these are (as Don Ho Says) "Tiny Bubbles
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Old 17-04-2011, 19:32   #5
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Re: Perkins 4108 fuel problem

I only use the electric pump to bleed the system.
The pick up tube seems leak free.The last attemp I had a straight run from the tank to the lift pump.
I will change out the rubber "olives" next.
Is it possible that a very small leak in the lift pump would let air into the system?
Thanks
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Old 17-04-2011, 19:44   #6
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Re: Perkins 4108 fuel problem

Yes indeed...I have had a few over the years....
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Old 17-04-2011, 21:26   #7
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Re: Perkins 4108 fuel problem

If your oil level is up 2", you better get rid of the oil before you burn the bearings and rings out of the engine.
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Old 19-04-2011, 06:08   #8
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Re: Perkins 4108 Fuel Problem

I had a very similar problem a while back that drove me to insanity, mine started with bad case of bug in the fuel, how many fuel filters do you have? I had 2 on the side of the engine and a fuel/ water separator and then another next to it and they where unnecessary so I removed filter no3 and it was that seemed have solved the situation, I dont think that your fuel lift pump is in any way connected to the internal side of your engine but for what it costs replace it, I don't think you need the electric fuel pump the psi is perfectly adequate I think its around 70 to pull the fuel around the engine, the chap above is correct check all olive joints nut bolt and screw, also any fuel filters you have if they are the glass bowled ones there are 3 rubber seals one where the glass clamps to the actual filter above and below and one in the top of the under side of the mechanism where you tighten up the screw (I think thats where my problem was)!!! I am not an engineer by any way shape or form, I found out after 3 months of utter frustration and lot of help from this forum, good luck!!!
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Old 19-04-2011, 06:33   #9
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Re: Perkins 4108 Fuel Problem

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Originally Posted by Wainui View Post
I suspect the lift pump may be leaking into the engine oil as the oil level seems to be 2'' higher than I remember.
Whoa! Two inches higher?!? That is a lot of extra fluid in your sump, and if it's due to fuel getting added, you certainly have a lift pump problem.

But, something I don't understand -- isn't your dipstick marked with a high and low mark? If it is, what does your memory have to do with your understanding of the oil level?

I would replace the fuel lift pump, change the oil, reconnect the rest of your system to it's normal configuration and see what happens.
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Old 19-04-2011, 07:01   #10
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Re: Perkins 4108 Fuel Problem

I stand by my comment I really dont think that it internally connected, does your oil smell of fuel, that should answer your question!!!
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Old 19-04-2011, 07:17   #11
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Re: Perkins 4108 Fuel Problem

The mechanical fuel lift pump is actuated by a lobe on the camshaft via a pushrod, which pushes a lever on the pump. The pump housing is bolted to the crankcase and the pump lever passes through an opening in the crankcase. A hole in the pump diaphragm will allow fuel to pass into the crankcase and collect in the oil sump.
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Old 19-04-2011, 08:03   #12
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Re: Perkins 4108 Fuel Problem

Doug I stand corrected, I did say I wasn't a mechanic!!!
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Old 19-04-2011, 08:24   #13
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Re: Perkins 4108 Fuel Problem

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Doug I stand corrected, I did say I wasn't a mechanic!!!
That's fine!

Perhaps, on the mechanical threads, it might be good to hold off on advice if you're not sure, because it just makes it harder for the more experienced voices to be heard.
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Old 19-04-2011, 08:31   #14
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Re: Perkins 4108 Fuel Problem

I don't necessarily agree with that Doug even those with all the so called knowledge can often be wrong, I took 3 marine mechanics to shrug which led me to eventually fix the engine my self, sometimes even a little knowledge can be invaluable, smiling tooo!! ;-)
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Old 02-05-2011, 13:06   #15
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Re: Perkins 4108 Fuel Problem

Many thanks to all who replied.
I replaced the mechanical fuel pump and changed the oil (3 quarts high) and fired her up. 20 mins later she reved up and died. I then ran a hose from a 5 gallon jug straight to the mechanical fuel pump and she ran fine. I then connected the hose to the pick up bypassing the racor and Purolator 12 electric pump and she ran for 20 mins and died. Problem must be in the pick up which is hard to get to and replace. I can blow through the pick up which makes the fuel in the tank bubble so there may be a tiny hole somewhere in the tank. I then reconnected the racor and wired the Purolater to the key switch so it runs when the engine is on, which seems to keep the engine running without any problems. I will replace the pick up at a later date but does anybody see any problems with a electric pump running in front of the mechanical pump?
Thanks
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