Air getting in the high pressure side

[KellysEye]

> Sure use talc to trace a diesel leak out but that is of no use in tracing an air leak in.

Talcum powder is used to check for a diesel leak not air in. The OP is looking for a diesel leak however if diesel leaks out air will get in, if it didn't the revs wouldn't change and the engine wouldn't eventually cut out. When we had copper pipes that happened a number of times so we changed them.

 

[tinkicker0]

I have a BMC 1.5 diesel engine in my boat and recently started to get problems with air getting into the high pressure side. After half an hour or so of running the engine starts to rev up all by its self every so often, so I will be running at 2000 rpm and it will jump up to about 2400 rpm for a couple of seconds and then back to 2000 rpm. I understand this is caused by lack of fuel. Then when I stop the engine it won't start again unless I bleed number 4 and 3 injector pipes.

I had a slight leak on number 4 injector pipe so replaced this with a new one, this hasn't solved the issue. I have checked all the low pressure side and no bubbles, I have bled the nut on the side of the injection pump and no bubbles.

Any ideas on where to look for a leak? It's starting to get annoying now. I'm suprised air would get in to the high pressure side while it's running.

The engine will not rev up due to a lack of fuel but indirectly because of it.

The engine bogs due to air in the hp side causing a loss of power, the governer being an all speed type opens up a bit to maintain rpm, then it gets a temporary clear bit of fuel and fires as it should, the revs rise quickly, then drop as the governer cuts fuel till the rpm is balanced with the power lever setting again.

This is call hunting or governer surge.

You are drawing air on the suction side.

 

[Nick Marine Eng]

I used to build these engines by the dozens at the boat yard I worked at, sounds like a fuel pressure problem, however have you checked the diafram in the lift pump. I dont know if this was looked at in the rebuild (proberly not) if the material gets a small split in it after a while the fuel preasure drops and air gets in the system as you described. Once the air is cleared and the engine running the cycle starts again. Other than checking all connections on the fuel lines up to the DPA pump then the Injectors themselves this would be my prosess of eliminating your faults.

nickroberts02@o2.co.uk