Engine won’t hold high power throttle settings

[poiu]

I have a Perkins M225ti. It’s a mechanical direct ignition 6 cylinder engine, turbocharged with a Bosch rotary VE fuel pump. What happens is the engine works fine until accelerated to about 1600 rpm (roughly 50% power) then it holds power for only a few seconds then the revs drop down to 1200 rpm and stay there in spite of the high throttle setting. The throttle can be reduced and revs stay at any setting up to 1400 or so, then can be increased again to 1600 or more only to repeat the process of dropping power.

We did pull the pump off recently to change the high pressure side O ring seal that was leaking and cleaned the pump out when we did it. It is now leak free. I don’t know if we disturbed anything in that process. We also checked for air leaks and there are none up to the fuel filter as no bubbles are seen, and all connections seem tight after the first stage Racor filter. The fuel pump is newly replaced.

Any ideas?

[Greatest Lakes]

Diesels generally do this whenever they are starved for fuel. It may be unrelated to your previous work, it's possible something is blocking the fuel pickup in the tank. It could also be a partial obstruction in a fuel injector or line around the pump. If the high pressure pump can't keep up, that could also be the cause.

[poiu]

Originally Posted by Greatest Lakes

Diesels generally do this whenever they are starved for fuel. It may be unrelated to your previous work, it's possible something is blocking the fuel pickup in the tank. It could also be a partial obstruction in a fuel injector or line around the pump. If the high pressure pump can't keep up, that could also be the cause.

Thanks. The engine runs sweetly. No vibration, so I expect all cylinders are firing equally and so the injectors are fine. No smoke also. I’ll check the secondary filters, although they should be good as they were changed recently. I think the pick up suggestion is good. It would correspond to the problem as it takes a while to drop revs, about 5 seconds, which may be the time it takes for the vacuum to build. It’s a long feed line from the tank with some rubber hose and maybe an air pocket in the Racor and secondary filter.

[Searles]

Place a can of fresh clean diesel close as possible to the filter feed the engine from thi plus return to the same ,this will quickly find if there is a tank or fuel line problem .⛵️⚓️

[poiu]

Originally Posted by Searles

Place a can of fresh clean diesel close as possible to the filter feed the engine from thi plus return to the same ,this will quickly find if there is a tank or fuel line problem .⛵️⚓️

Thanks.

Another feature of this problem is I can get full revs in neural gear, but not under load, but as fuel demand under load is hugely more I can see a fuel restriction is likely.

[skipperpete]

Originally Posted by poiu

I have a Perkins M225ti. It’s a mechanical direct ignition 6 cylinder engine, turbocharged with a Bosch rotary VE fuel pump. What happens is the engine works fine until accelerated to about 1600 rpm (roughly 50% power) then it holds power for only a few seconds then the revs drop down to 1200 rpm and stay there in spite of the high throttle setting. The throttle can be reduced and revs stay at any setting up to 1400 or so, then can be increased again to 1600 or more only to repeat the process of dropping power.



We did pull the pump off recently to change the high pressure side O ring seal that was leaking and cleaned the pump out when we did it. It is now leak free. I don’t know if we disturbed anything in that process. We also checked for air leaks and there are none up to the fuel filter as no bubbles are seen, and all connections seem tight after the first stage Racor filter. The fuel pump is newly replaced.



Any ideas?

Just so I understand...... you stripped and rebuilt the VE yourself? Or did you get it repaired by a pump technician?
There are a host of things that will cause the problem you describe and assuming from the beginning that the fuel supply from the tank to the injector pump is completely as it should be, ( no suction leaks or restrictions) consider these possibilities.
The turbo could be seized or otherwise damaged
The waste gate could be jammed open
The intercooler could be blocked
The turbo fuel boost line to the injector pump is broken
If you did the pump repair yourself you might have built a problem into it yourself.
Is there any exhaust smoke?
Is it possible the prop is fouled (or having pitch related problems if it’s a feathering or CP propeller)
Do you run any accessories off the front of the crankshaft? Hydraulics or high output alternator ( its a long shot but deserves a mention).
The list is even longer but these are the points worth considering in the short term

[jamhass]

Throttle cable and linkages?

[poiu]

Originally Posted by jamhass

Throttle cable and linkages?

That is fine. It smoothly goes to and hold any rev setting in neutral. The problem only appears under load.

[poiu]

Originally Posted by skipperpete

Just so I understand...... you stripped and rebuilt the VE yourself? Or did you get it repaired by a pump technician?
There are a host of things that will cause the problem you describe and assuming from the beginning that the fuel supply from the tank to the injector pump is completely as it should be, ( no suction leaks or restrictions) consider these possibilities.
The turbo could be seized or otherwise damaged
The waste gate could be jammed open
The intercooler could be blocked
The turbo fuel boost line to the injector pump is broken
If you did the pump repair yourself you might have built a problem into it yourself.
Is there any exhaust smoke?
Is it possible the prop is fouled (or having pitch related problems if it’s a feathering or CP propeller)
Do you run any accessories off the front of the crankshaft? Hydraulics or high output alternator ( its a long shot but deserves a mention).
The list is even longer but these are the points worth considering in the short term

Yes, we changed the O ring on the pump and could have done some damage, but we don't think so.


We also took the turbo off to change a thru-hull next to the engine, but it seems to spin up fine and the pipe to the injector pump diaphragm seems OK. If the turbo was not functioning the revs would hold at a power setting and not drop off like they do I expect?


The prop is fine.



There is no exhaust smoke.


I don't think the intercooler is a problem as if the intercooler was blocked I would expect black smoke from inadequate air.



Ditto if the turbo didn't boost enough for example with a jammed open waste gate, would it not be so? The turbo whistles a bit as usual, so I think it works OK.

[sailorboy1]

Originally Posted by poiu

Thanks.

Another feature of this problem is I can get full revs in neural gear, but not under load, but as fuel demand under load is hugely more I can see a fuel restriction is likely.

I feel that is pretty much meaningless.

I feel you problem is almost surely something preventing the engine from getting fuel. This is a common problem and there are lots of threads. The only real way to rule out it being a supply problem of an engine problem is to run the engine under load using a know clean supply of fuel.

[skipperpete]

I forgot to ask...... did this rpm problem exist prior to the injector pump repair or did it only show up afterwards?
Was the Oring the one between the hydraulic head and the pump housing?

[SV Confianza]

Originally Posted by Searles

Place a can of fresh clean diesel close as possible to the filter feed the engine from thi plus return to the same ,this will quickly find if there is a tank or fuel line problem .⛵️⚓️

I would agree that this is the first trouble shooting step. Start eliminating problems. Work your way down the fuel system. Could even be a blockage in the fuel tank vent.

First eliminate the fuel supply part of the system, then get into the more complicated problems.

[poiu]

Originally Posted by skipperpete

I forgot to ask...... did this rpm problem exist prior to the injector pump repair or did it only show up afterwards?
Was the Oring the one between the hydraulic head and the pump housing?

The problem showed up two months after the pump seal was changed, but it was possible we never took it into the rev range where the engine gives up.

Yes to the second question.