Kelvin P4 loss of power and surging

[Catnip King]

Hi all,

I am trying to figure out a problem with my Kelvin P4. Been messing around I've serviced the engine hoping new fuel filters might have sorted this issue out but it hasn't 

Basically when running engine at idle it will run smooth for a little while then it sounds as though it is dying and then suddenly bursts into action again but slightly faster idle until it calms back down again. Also when running under load engine will be fine but sound as though it is dying again and suddenly regain speed; sometimes it will stall. Once it gets like this it seems to continue. Sometimes it will run fine for a good 30mins. So it speeds up slows down speeds up slows down etc. 

When I run engine in idle and give it a blast of revs it seems to make the problem go away for a short while.

I am wondering what I should be looking at...

I've contacted many engineers who don't want to look at it or simply want me to remove the engine to send to them which isn't an option. I need to try and fix it myself.

Thanks

[MtB]

More knowledgeable people will be along shortly, but in the interim my opinion is this will be a fuel problem.

Conventional wisdom is that symptoms like this are caused by air is getting into the fuel line. This will obviously mess up the injection volumes. Or there is a serious blockage in the fuel line to the injector pump. 

I imagine you have a day tank and the fuel is gravity fed though, so there is no fuel supply pump to be sucking in air. Similarly there is not much scope for a blockage. Have you disconnected the fuel line into the pump to check it runs freely?

Final though is this might be diesel bug or water in the day tank. How clean does the fuel look, when you run off a sample from the day tank?

[Catnip King]

Hi Mike thanks for your reply. It is fed from the main diesel tank not day tank. It has a manual lift pump going to fuel filter then to injectors.  I have disconnected supply after the filter to make sure when I use the lever on the lift pump that diesel is coming through which it is. I haven't actually looked at the diesel quality though so maybe this is something I need to do then.

[MtB]

Ah well in that case back to conventional wisdom. Most probably an air leak in the fuel supply line somewhere. Somewhat less likely is diesel bug and/or water in the fuel.

Can you jury-rig up a different fuel supply using, say, a oil can fixed to something above the engine so there is a gravity supply under positive pressure, of known clean fuel? If the fault vanishes with this, then you'll know you're on the right track. 

[Catnip King]

Thanks Mike. I can do that sounds a good plan. Should I rig it up after the lift pump then as it will be gravity fed?

[MtB]

Just now, Catnip King said:

Thanks Mike. I can do that sounds a good plan. Should I rig it up after the lift pump then as it will be gravity fed?

 

Yes. Bung the temp fuel line straight into the injector pump so the lift pump is out of the equation too. 

Hopefully Tony Brooks will be along shortly to patiently correct everything I've suggested!

[MtB]

P.S. cap off or disconnect the supply to the lift pump too though, as it will still otherwise be connected to the normal fuel tank!

[Catnip King]

Thanks will do. Will report back with how it goes will be 3-5 days though as need to get some bits sorted to do it and need to it around time I work. Cheers!

[David Mack]

And if its not fuel, is it possibly something sticking in the governor?

 

[MtB]

15 minutes ago, David Mack said:

And if its not fuel, is it possibly something sticking in the governor?

 

 

Unlikely, given the OP says this:

"Basically when running engine at idle it will run smooth for a little while then it sounds as though it is dying and then suddenly bursts into action again"

[Catnip King]

I don't think it will be that but I will check after I have tested with a temporary tank. One thing I am wondering though is what are the chances of it being something else unrelated to the fuel? I mean internally inside the engine not the injector pump... 

[Catnip King]

Another symptom I should mention is it will sometimes be under load at about half revs then seem to drop to tickover speed. No matter how much I play with the throttle it doesn't pick up again until I take it out of gear then put it back into gear again.

[Catnip King]

So I hooked up seperate tank gravity fed and for a moment I thought it was sorted but unfortunately its not. Once engine warmed up the problem started again. I can't figure out whats causing it

[Catnip King]

I thought I would update here engine is running sweet now. Main issue was what I didn't expect inside injector pump the rack was gunked up a bit and not sliding properly. Also redoing the valve clearances made a massive improvement on the engine much better sound and less smoke. So I am a happy man.