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Old 01-05-2015, 18:30   #1
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Perkins 4108 air leak?

Hey everybody,

I have been struggling for months with a seemingly common but new-to-me problem with my Perkins 4.108 - let's call it the SAD syndrome, surge and die. At what appears to be totally random points in operation, the engine suddenly revs up to say 3000rpm in less than a second and then dies immediately. It can sometimes be restarted without bleeding it, but it never lasted long - minutes after restarting it will die again, this time it can't be restarted and needs to be bled.

When the problem first occurred, it was a single event and I pinned it on sludge on the bottom of the tank and clogged fuel filters. The previous owners of the boat altered the pump and filter layout; I have an electric fuel pump and two racor glass bowl type filters as a primary and a secondary with 10 and 30 micron elements. The lift pump and the original secondary fuel filter are disconnected. The setup is very simple: Fuel tank pickup --> primary filter --> secondary filter --> fuel pump --> T-connector to cold weather injection --> injector pump --> injectors.

The frequency of these incidents increased over the last 8 weeks. Now, I can almost win every bet that the engine will die less then 2 minutes after start when it sat for more then a day. The tank is clean, the fuel is clean and so are the filters. I suspected an air leak on the Racors top locking screw gaskets because sometimes (but not always!) the fuel level in the filter housings is dangerously low, like, almost at the fuel line pick up or even below which would cause the pump to suck air. But replacing everything many times and jury rigging bigger, thicker gaskets didn't help, and the engine still fails randomly. I tried different micron ratings from 5 micron to 30 micron. I checked the fuel lines and couldn't find a leak. I even suspected a clogged fuel tank vent was building vacuum in the tank so I opened the filler cap from time to time with no effect. I have a vacuum gauge mounted on the primary which shows normal values. Sometimes the engine runs for 8-10 hours straight with no problems. Sometimes I have no issues for a week. But mostly, the surge and die occurs right after start up. Mostly, it is accompanied with very low fuel levels in the filters, so that I assume the problem has to be in the fuel tank to primary filter part of the system.
I am at the end of my wits.

Has anyone experienced something like this? Any hints?
Thanks!
Daniel
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Old 01-05-2015, 19:27   #2
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Re: Perkins 4108 air leak?

On our boat, that problem is because the fuel tank/selector valves are leaking air around the stem.
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Old 01-05-2015, 19:29   #3
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Re: Perkins 4108 air leak?

This type of problem with the 4-108 (and other diesels) can indeed be maddening.

Somewhere, somehow, air is getting into the system. When it reaches the injection pump, bingo....surges and shutdown. Sometimes the engine will "hunt"....rpms going up and down repeatedly until it finally stops.

One usual culprit is the on-engine fuel pump, but it sounds like yours has been bypassed.

Check all hose connections carefully...be sure the clamps are tight.

Years ago I had a problem I couldn't find for months, but finally located a pinhole on the bottom of a copper fuel line running through the bilge! On a very quiet day I was manually activating the pump lever on the on-engine fuel pump and could hear a soft hissing. Traced it down with my fingers under the copper fuel line until I located the pinhole.

Just today I solved an air leak problem on my generator. A new electric fuel pump was installed and in the process one of the very short and contorted (90-degree bend) 5/16" fuel hoses wasn't seated perfectly, and the hose clamps couldn't make a 100% perfect connection. Cut a new length of fuel hose, made sure it was perfectly fitted to the nipples, used new AWAB hose clamps, tightened everything and....bingo...no more air leak. I hope.

Good luck with your problem. Only thing to do is to keep checking. By the way, your Racor filters should NEVER be low. They should always be full, and the fuel should look perfectly clean. You may have a problem with the fuel pickup line in the tank, or maybe with the fuel pump being unable to make the lift (weak or loose connections).

Bill
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Old 01-05-2015, 19:33   #4
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Re: Perkins 4108 air leak?

Yes, had same problem. It is air in the lines. I replaced all lines and lift pump. Only after I bypassed the primary racor filter did problem go away. I took it apart over the winter and as far as I can see the drain was not completely closed. If that does not work I will replace. I was told by TAD never to use an electric fuel pump with Perkins 4108 BTW.
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Old 01-05-2015, 21:57   #5
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Re: Perkins 4108 air leak?

A vacuum (negative pressure) leak is indeed difficult to find, may be anywhere and since it does not leak anything out, nothing shows.
You mentioned changing all the gaskets or 'o' rings on the Racors. Looked at the plastic bowl for any cracks, etc?
Here is an idea: Disconnect the thin fuel hose at the tank that feeds the filters, insert a tire air valve into it by shaving the rubber part to make it fit into the hose and clamp it. Now, with a bicycle hand pump, put some positive pressure into it. Take off the pump and try to listen for a hiss anywhere.
If no hiss is heard, then make a mixture of 1 capful of dishwashing soap into a spray bottle with water and mist it onto all the hoses, filters and fuel lines and again pump some more air into the intake line with the valve you just added. Keep up the pressure this time and spray some more soapy water.
Bubbles should appear where air is escaping, or fuel would seep since now it's been pushed out and wiping the lines with a white napkin, the fuel leak would show well after a few wipes.
Hope this simplifies the search. It's easier and more economical than replacing a bunch of hoses, gaskets, fittings, '0'rings, olives, etc. and all those lines would be cleaner on the outside too!.
Can find those discarded tire valves on the ground at any tire shop.
Good luck.
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Old 01-05-2015, 22:09   #6
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Re: Perkins 4108 air leak?

A vacuum (negative pressure) leak is indeed difficult to find, may be anywhere and since it does not leak anything out, nothing shows.
You mentioned changing all the gaskets or 'o' rings on the Racors. Looked at the plastic bowl for any cracks, etc?
Here is an idea: Disconnect the thin fuel hose at the tank that feeds the filters, insert a tire air valve into it by shaving the rubber part to make it fit into the hose and clamp it. Now, with a bicycle hand pump, put some positive pressure into it. Take off the pump and try to listen for a hiss anywhere.
If no hiss is heard, then make a mixture of 1 capful of dishwashing soap into a spray bottle with water and mist it onto all the hoses, filters and fuel lines and again pump some more air into the intake line with the valve you just added. Keep up the pressure this time and spray some more soapy water.
Bubbles should appear where air is escaping, or fuel would seep since now it's been pushed out and wiping the lines with a white napkin, the fuel leak would show well after a few wipes.
Hope this simplifies the search. It's easier and more economical than replacing a bunch of hoses, gaskets, fittings, '0'rings, olives, etc. and all those lines would be cleaner on the outside too!.
Can find those discarded tire valves on the ground at any tire shop.
Good luck.
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Old 01-05-2015, 22:45   #7
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Re: Perkins 4108 air leak?

Having a Perkins and I think having experienced every deisel failure known to mankind I can empathise here.
Re install a new manual lift pump and then place the electric pump in front of all the filters. If you place it straight after the fuel pick up on the tank it will give your system positive pressure from the tank when switched on - and as a previous post advised this will give you a chance to see leaks of deisel as opposed to air being sucked in. Problem solving made easy. Well easier. It also allows you to bleed filters and systems easily. Under normal running the manual lift will then do the sucking and pumping and if you ever get air being sucked in the system pre manual filter you can temporarily emeliorate it by flipping on the electric pump and then problem solve quickly.
Hope you get this figured out and this helps the thought process.
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Old 02-05-2015, 08:45   #8
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Re: Perkins 4108 air leak?

I had a problem which was similar. Engine would die at rare times. With a hydraulic lock on the shaft, connected to the tranny seal plate, one time, the sudden stop cracked the seal plate.
It took a year, but one time, I used an electric pump to pressure the entire fuel line system. In my case, it was the fuel lift pump gasket. The fuel just squirted out and it was very visible. It was an easy fix after I found it. I would suggest you try a pressure test with using a pump and diesel, not air to create the pressure. Good luck.
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Old 02-05-2015, 09:52   #9
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Re: Perkins 4108 air leak?

Why would someone advise to never use an electric fuel pump on the fuel system for a Perkins 4108. Over the years I have had two boats both with Perkins 4108 engines with electric fuel pumps and no problems.
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Old 02-05-2015, 14:42   #10
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Re: Perkins 4108 air leak?

Had a similar problem after placing a vacuum gauge on our Racor. I suggest you remove it and replace with the original T handle and see if the problem goes away. Ours did. Found out that the vacuum gauge sold to me in St. Martin at Island Water World was for a 900 Racor and despite assurances that it should work on the 500 series it did not. Barring total removal if you feel the gauge you have does work, I suggest trying a gas vapor proof type thread lock on the pressure gauge.
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Old 02-05-2015, 16:37   #11
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Re: Perkins 4108 air leak?

Its not necessarily air in the line. I've experienced similar symptoms when a piece of black crud from the tank almost completely blocked the fuel line at a 90 deg. elbow. After dying the first time it would start and run for seconds, surge and die. We bypassed that section of fuel line and later blew the crud out with air from a diving tank. Check also to make sure your tank vent is not blocked by mud wasps.
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Old 02-05-2015, 17:21   #12
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Re: Perkins 4108 air leak?

Take a look also at the air intake - the thing that looks like a "muffin" on top the engine. Some folks will put a piece of oily rag in there during layup. I have heard of engines behaving erratically like so when the rag got sucked into the air intake ! Or - mud wasps ? ... or their nest ?
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Old 02-05-2015, 17:27   #13
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Re: Perkins 4108 air leak?

Quote:
Originally Posted by Sailing Partner View Post
Why would someone advise to never use an electric fuel pump on the fuel system for a Perkins 4108. Over the years I have had two boats both with Perkins 4108 engines with electric fuel pumps and no problems.
So annoying when being told never do this or that then giving no reason; I say, share the knowledge, won't hurt OR maybe they don't know just passing misinformation.
Trouble is, you find this in OEM manuals too, uggh !
Jack
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Old 02-05-2015, 18:02   #14
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Re: Perkins 4108 air leak?

I have a friend from France who installed an elec fuel pump on his volvo this year. I like the idea- probably less "guessing" if there is a fuel flow problem someplace. However, I do know that when those engines were built (Perkins 4-108's anyway) - elec fuel delivery was not exactly ready for everyone yet. Also, the engines were built with mechanical fuel pumps and mechanical water pumps that were engineered to deliver a proper amount of fuel to suit the engine rpm's. Higher rpm makes the mechanical pump deliver more fuel. The concern I have with elec is matching the proper fuel flow to the engine rpm. Although they will work (at least for a while) at a constant low pressure - I'm not sure what effect a constant pressure would have on the rest of the fuel components downstream from the elec pump.
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Old 03-05-2015, 00:46   #15
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Re: Perkins 4108 air leak?

Quote:
Originally Posted by northiceman View Post
I have a friend from France who installed an elec fuel pump on his volvo this year. I like the idea- probably less "guessing" if there is a fuel flow problem someplace. However, I do know that when those engines were built (Perkins 4-108's anyway) - elec fuel delivery was not exactly ready for everyone yet. Also, the engines were built with mechanical fuel pumps and mechanical water pumps that were engineered to deliver a proper amount of fuel to suit the engine rpm's. Higher rpm makes the mechanical pump deliver more fuel. The concern I have with elec is matching the proper fuel flow to the engine rpm. Although they will work (at least for a while) at a constant low pressure - I'm not sure what effect a constant pressure would have on the rest of the fuel components downstream from the elec pump.
Volvo boat engine ? Diesel ? Elect. high press. pump or lift pump ? I'm not sure what you're saying here, seems like you're confusing the lift pump w/the high press. injector pump.
Jack
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