Why MD7A is doing this?

[metancetre]

Hello everyone!

Here is the video;

Looking for all kind of suggestions except throw this old engine away as i love my old friend and so far he was so reliable

When i start the engine it runs like a normal (idle) then rpm increasing and normal up and normal, then it goes up and at certain point engine stops. If you watch the video you see it starts at idle and goes up. Always similar pattern.

What i did so far;

New water separator with pre-fuel filter installed (as my old lift pump was so dirty)
New lifting pump installed.
Did bleed the system but i have never seen an air bubble free fuel lines on this engine so i assume little bit air running through is ok or i should look for air leakage?

Also if there is air in the system engine should loose power right not increase the rpm?

Today i started to think that maybe injectors are not working well and spraying too much fuel and after certain point it is too much fuel and engine stops.

I have bosh injection pump installed, i am not sure if it has problem (hopefully not).

Thanks!

 

[jobbie]

Watched a youtube video and they had a similar problem, it was a diesel bug blockage in the fuel pick up pipe in the tank.

Link to video below.... skip to the end to see what the issue was it may help.

 

[QBhoy]

Hi
You shouldn’t have air in your fuel system delivery at all.
but more of a concern is that if you are saying that the engine is increasing rpm on its own and throttle position is at lowest idle setting at both remote and engine...you may be experiencing what’s called dieseling or runaway. Have a google at that. It’s not good and can be dangerously catastrophic for engine and anyone nearby

 

[QBhoy]

Hi
You shouldn’t have air in your fuel system delivery at all.
but more of a concern is that if you are saying that the engine is increasing rpm on its own and throttle position is at lowest idle setting at both remote and engine...you may be experiencing what’s called dieseling or runaway. Have a google at that. It’s not good and can be dangerously catastrophic for engine and anyone nearby

Basically it’s running on its own oil if so. Very dangerous situation.

 

[vyv_cox]

I dont think this is runaway. It would continue increasing speed to very high levels in that case.
It is almost certainly air in the fuel but this can be caused by bug in the tank. The pump is trying to suck fuel but cannot because the tank exit is partially blocked. It draws in air from any poor seal, e.g at the primary filter bowl. After the engine stops some fuel flows into the hose, allowing it to restart and run for a short time.

 

[Graham_Wright]

Hello everyone!

Here is the video;

Looking for all kind of suggestions except throw this old engine away as i love my old friend and so far he was so reliable

When i start the engine it runs like a normal (idle) then rpm increasing and normal up and normal, then it goes up and at certain point engine stops. If you watch the video you see it starts at idle and goes up. Always similar pattern.

What i did so far;

New water separator with pre-fuel filter installed (as my old lift pump was so dirty)
New lifting pump installed.
Did bleed the system but i have never seen an air bubble free fuel lines on this engine so i assume little bit air running through is ok or i should look for air leakage?

Also if there is air in the system engine should loose power right not increase the rpm?

Today i started to think that maybe injectors are not working well and spraying too much fuel and after certain point it is too much fuel and engine stops.

I have bosh injection pump installed, i am not sure if it has problem (hopefully not).

Thanks!

This is a classic of air entry. Same happens with my engine. I have an air interceptor and, if I forget to bleed it, the engine does as your does. If I catch it in time and bleed the interceptor, it recovers. Otherwise, about half a minute cranking (even without bleeding anything or cracking the injectors), it will start and run again.

 

[QBhoy]

I dont think this is runaway. It would continue increasing speed to very high levels in that case.
It is almost certainly air in the fuel but this can be caused by bug in the tank. The pump is trying to suck fuel but cannot because the tank exit is partially blocked. It draws in air from any poor seal, e.g at the primary filter bowl. After the engine stops some fuel flows into the hose, allowing it to restart and run for a short time.

Agree it’s likely air, but unusual to do this of throttle is at idle.
dieseling can do just this. The ultimate worst case of the effect is runaway when it increases beyond anything normal to destruction, of course. But lesser effects are often shown first.

 

[Graham376]

If the pipework allows and you have some fuel hose, connect it to the pump inlet pipe and stick the other end in a can of clean fuel and see how it runs.

 

[Iliade]

My vote goes for diesel bug - hydraulically governed injectors seem to exhibit this behaviour when bugged. Fresh filters and a shock treatment of bug killer sorted my boat's similar issue .

It certainly doesn't sound like runaway. I have only once been near to an engine that did that and it blew holes in the workshop roof!
e.g.

 

[Bilgediver]

Hello everyone!

Here is the video;

Looking for all kind of suggestions except throw this old engine away as i love my old friend and so far he was so reliable

When i start the engine it runs like a normal (idle) then rpm increasing and normal up and normal, then it goes up and at certain point engine stops. If you watch the video you see it starts at idle and goes up. Always similar pattern.

What i did so far;

New water separator with pre-fuel filter installed (as my old lift pump was so dirty)
New lifting pump installed.
Did bleed the system but i have never seen an air bubble free fuel lines on this engine so i assume little bit air running through is ok or i should look for air leakage?

Also if there is air in the system engine should loose power right not increase the rpm?

Today i started to think that maybe injectors are not working well and spraying too much fuel and after certain point it is too much fuel and engine stops.

I have bosh injection pump installed, i am not sure if it has problem (hopefully not).

Thanks!

Sounds like the engine is either responding to a false speed / throttle signal or there is a governor problem. Nothing wrong with injectors etc. Try watching the speed control lever at the fuel pump and see if it is moving due to a slack connection when these speed excursions occur. If not then see if you can find a fuel injection specialist who can service the pump. Spares for these pumps can be difficult to obtain however sometimes a good service engineer can sort things out.

This engine is receiving varying speed signals and responding to them in a governed condition so unlikely to be air.

 

[vyv_cox]

Sounds like the engine is either responding to a false speed / throttle signal or there is a governor problem. Nothing wrong with injectors etc. Try watching the speed control lever at the fuel pump and see if it is moving due to a slack connection when these speed excursions occur. If not then see if you can find a fuel injection specialist who can service the pump. Spares for these pumps can be difficult to obtain however sometimes a good service engineer can sort things out.

This engine is receiving varying speed signals and responding to them in a governed condition so unlikely to be air.

My principle is to try the easy solutions first. The OP tells us he always sees air in the fuel line. This is clearly not as it should be, so fix that first. If that fails to solve the problem then by all means move on to technical and expensive solutions.

 

[metancetre]

Hello Everyone!

It is fixed thanks to you all!
It was the clogged tank sucking line! What jobbie and vyv_cox said was exactly happening. System was trying to suck and getting air from the water separator inlet as it is the weakest in my system. Thanks thanks thanks!

I made a plan and went onboard today and went inside the small hatch on the port side and took the suction line out from the tank.
As soon as I took it off, black jelly dirt came out then I took my hand pump and connected and started to suck a a lot.
It is like a ketchup first small pieces then more and boom big dirt came out. Then clean fuel started to come.
I connected everything, did bleed the system and now working better than ever.

Once again thanks everyone and yes vyv_cox one more time I learned that always start with the simplest and cheapest one

 

[Iliade]

The jelly is diesel bug. I would shock treat the tank.

 

[vyv_cox]

The jelly is diesel bug. I would shock treat the tank.

Definitely. Add some diesel bug treatment after draining any water from the bottom of the tank. A Pela is useful for this as it can reach right to the bottom, below the take-off for the fuel.

 

[metancetre]

Definitely. Add some diesel bug treatment after draining any water from the bottom of the tank. A Pela is useful for this as it can reach right to the bottom, below the take-off for the fuel.

A good tank cleaning is on my to do list! thanks!