Perkins 4.108 - Expert Advise Needed

[Seman]

I’m having problems with my Perkins 4.108
The engine won’t start when cold, (we are in the tropics), unless I open the air vent screw on top of the anti stall device for a second whilst the starter motor is turning the engine over.
This way it will start immediately.
It is not a starter motor or battery problem.
I have been battling with this for the past 400 engine hours.
The engine runs perfectly. I don’t have any, not even minor, diesel leaks.
Could there be air in the system ? I can only see fuel dripping out of the vent screw when opened.
I assume, if air is trapped somewhere in the system, it would be pushed through when the motor is running?
Could there be a diesel non return valve leaking, allowing the diesel to run back into the tank when the motor is stopped?
I have replaced the fuel lift pump, it makes no difference.
Any help would be greatly appreciated.
Thank you very much.

[Chief Engineer]

Sound like you have air getting into the suction side of the fuel pump.

This could be due to bad connections, bad or missing o-rings in filters or bad olives (o-rings) on the fuel lines at the lift pump.

Some perkins return lines go back to the secondary filter and to the tank.

I have seen what I call champagne bubbles accumulate in the secondary filters on Yanmars and Perkins........these are due to miniscule leaks on the vacuum side of the lift pump/if you have a Racor Filter, check the clear housing for small cracks.

[perchance]

Check the vacuum on the suction side of the fuel system. Don't know what it is supposed to be but you may have a restriction somewhere in the system.

[S/V_Surya]

This symptom has been discussed and typically caused by filter change and reconnection not tight enough resulting in air introduction. Did you change your filters about 400 hours ago? When you shut it down air allows fuel to drain back into the tank and thus fill fuel line with air.

[Seman]

Thank you for your input.
I did change the diesel filters 400 hours ago.
But I just changed them again yesterday, including replacing all "o" rings, makes no difference.
How can I detect a minor air leak in the suction line?

[Seman]

Hello chief
Thank you very much for your input.
The problem appeared to start after replacing the diesel filters. I've just replaced them again, including relacing all "O" rings, no difference.

How can locate a small air leak in the suction line?
Thank youvery much,
Seman

[shakey doug]

Prior to startup, undo hp leads at injectors move stop lever to full run position AT pump put throttle to full have some one crank engine watch for immediate flow at injector ends if no flow give fuel pump a couple of solid hits on top where the throttle and stop levers are located you may have a sticking throttle valve .If no success check filter & valves in fuel lift pump also secondary filter non-return valve. Next check fuel supply plumbing for air leaks as already mentioned.Do motor rpms osolate at idle or at low revs?

[shakey doug]

Disconnect fuel supply line at hp pump run a hose into a clear container 1/4 full of diesel submerge hose end then use lift pump any bubbles can be seen exiting hose end. You may have rotate engine grank to put pump pecker on back of cam to obtain full flow.

[Chief Engineer]

Lets work on isolation.

Get a container of clean fuel

Disconnect fuel line at pump inlet....no primary filter...no fuel tank

Put a piece of good fuel line into container

Run engine...report back

[Seman]

Thank you all very much for your help.
She is starting after 5-6 revolutions. Great! Still not sure where excactly the problem was, but must have been air, as you suggested.
Loosened & re-tightened all connections again & this time she started.
Thank you all again,
Seman