Perkins 4108 Bleeding Problem

[JulianGullsway]

Help !!!! This is driving me insane, every so often my engine wont start, I go through the whole process of bleeding it, then in runs very well for about 2 weeks, or days then the whole thing happens again, I have opened the fuel tank and it was infested with "The bug" cleaned it thoroughly changed the filters 3 - 4 time over, then the same thing happened again, so I replaced the fuel lift pump and it worked fine then a phew weeks later it stopped again where could this air be coming from, any ideas this ahas stumped my Marine engineer to the point where he has stopped charging!!!!!!!! Do I get a new engine?

[Laidback]

First Suspect : You have an air leak in the delivery system ! somewhere a connection is NOT good, between shutdown and start up - air replaces diesel.
Go over the whole fuel delivery system replacing
soft washers, tightening glands etc etc - Look for bubbles!
Get a new mechanic who knows what he is doing.

[roberttigar]

Air leak is probably correct. Suggest you check...
Racor bowl fot cracks-especially around the drain tap.
Fuel line that goes into the secondary filter housing. This is an npt tap (on my 4.108) and must be sealed properly.

Bob

[JulianGullsway]

Where though, I have bled the system so many times checked the bowls under the filters tightened up all joints etc!!!

[JulianGullsway]

Cheers Bob I will check that!!

[Laidback]

Originally Posted by JulianGullsway

Where though, I have bled the system so many times checked the bowls under the filters tightened up all joints etc!!!

It's not bleeding the system that is required - All the components of the system:
Filters . gaskets, lines, nuts, bolts, washers have to function as per SPECIFICATION - these must be checked replaced and re-secured so that air cannot enter the system.

[clsailor]

I had the same problem with my 4-108. Mechanic found a hairline crack in the #1 injector fuel line.

[billwa]

I had a similar problem on mine (4107). Eventually I replaced the aluminium washers on a few critical fittings with fibre washers that the PO left in the tool kit with fuel pump parts. I was having fuel leaks even with brand new aluminium, and couldnt source copper.

Also put a tap on the return fuel line and I shut both main tank and return taps on shutoff. I believe this gives less opportunity for a leak, as you need two holes (hole being any part of the line open to the atmosphere) for an air leak, and will only get air bubbles between the two holes... I cant swear that this is correct, anybody like to comment?

[Dynamo1181]

Try stopping up the tank vent & return line and pressurizing the system, looking for a leak. You may have to work in sections with this method. If air is going in then fuel should come out.
A

[btrayfors]

I feel your pain! Been there, done that with my 4-108. It was driving me crazy.

One day, after bleeding and checking and backing and filling I was pumping the little lever on the fuel pump and....

....heard a little whoosh, whoosh.

It was very quiet in the marina or I would never have heard it.

Turned out to be a pinhole in the BOTTOM of the copper fuel line. This line ran low in the bilge, was often in water from the occasional stuffing box leak, and had corroded. Found it with my fingers (stopping the whoosh whoosh sound); it wasn't visible.

Replaced the copper line with a high-quality fuel hose. No problems since (about 15 years).

Good luck...it's sure to be an air leak somewhere.

Bill

[JulianGullsway]

I am meeting the mechanic tomorrow, so I will suggest all these points.
Thank you all!!!!

[jdeatsch]

As an aside, in case someone doesn't know this, in the diesel engine world of equipment we used to use chassis grease on the connections until we found the issue. If the grease moves you've found the issue.

I'm not entirely certain this technique would be of much help in the case where the prime is leaking off as is apparently the case here.

I must say I like the idea of step by step going through the whole shootin' match.

So what did the mechanic have to say?

Jim

[olaf hart]

I would run a temporary hose from the tank to the lift pump, assuming the tank is reasonably clean.

If that fixed the problem I would replace all the lines and filters I bypassed.

If it continues, you need to look again at engine pump, lines and secondary filter.

My money is on a missing or cracked seal in a primary filter.

[barboak]

On my 4-107 after 5 years with this issue I found a mechanic in Gloucester, Ma who asked me right off if there was a pick up tube on the return line where it enters the tank. We pulled the return fitting and braised a piece of copper tube to it, no more problem. It seems as if sometimes when the engine shuts down it sucks air out of the return

[Anomaly]

Originally Posted by btrayfors

One day, after bleeding and checking and backing and filling I was pumping the little lever on the fuel pump and....

....heard a little whoosh, whoosh.

Bill

I hear this same noise on my 4-108 when pumping the same little lever on the fuel pump.... but I don't experience the problem the OP reported. But that may be because I haven't let it sit as long between start ups as in his case. I am assuming I shouldn't hear a sound that sounds (faintly) like air... but managed to get the boat from FL to RI this summer running the engine most days and then hauled it out... Will the pressurization routine suggested in this thread work/help to locate a minute crack?

Thanks,