4108 down on power

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sjdtuk

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My 4108 is down on power and I am trying to work out why. I would be very grateful is someone can up up with some good ideas to
try and get my power back.

Until last year it was working very well and was very easy to start. Even when cold, it would start within about 5 seconds and instantly when warm.
Under load, the egine woud run at 2300 revs.

Now.
It might take 30 seconds or more to start when cold. When warm, it still starts first press.
The boat is overpropped(and needs to be for manouverability). However, I now struggle to get more than 2000 rpm under load.

I have cleaned the air intake.
Repleaced fuel filters.
Made sure that all the fuel lines from the CAV pump are unobstructed.
Checked the injectors.
Replace the exhaust elbow which was corroded.
Checked that cambox pressure release valve on the CAV pump passes some fuel - you can blob through it.
I have an electric fuel pump, in addition to the mechanical lift pump. Switching this one seems to make no difference.
When running, the engine is reasonalby smooth - but not quite so smooth as before.

Any ideas?

Thanks

Stephen
 
Air in fuel

The symptoms are consistant with air in the fuel. Check all connections between tank intake and injection pump. For testing purpose, install a see-through pipe just before the injection pump, you can then check if there is air in the fuel.
Good luck,
Horst
 
Check the exhaust for partial blockage. Probably the area where the cooling seawater is injected is prime suspect. Also check rubber hose as it may have delaminated and be horrible inside even if it looks OK from outside.
 
I assume he changed the exhaust elbow as part of the investigative process - sorry, I glossed over that entry. Mine has water injected to a bell way down the system so I wasn't focused!
 
4108's are great engines that will run and run as long as there is lube oil , clean fuel and air. I'd have a good look at your fuel then see if there is air in it. Did you do anything at all to the fuel system over the winter?
 
Changed the fuels filters the year before. The engine ran well for quite a time after this.
The lift pump is reasonably recent as is the electric backup.

Stephen
 
If you replaced the exhaust elbow because of corrosion, was it back leaking and could you have a bit of pitting on exhaust valve seats,
Compression test would obviously show it up.
 
When you say you checked the injectors do you mean you pulled them and had them tested on a test rig?
Air in fuel and filter blockage tend to cause erratic running (hunting).
(Thinking aloud here) Could the injector pump timing have changed? Or governor set up? A quick google of this engines fuel pump reveals there is a maximum speed screw set by the manufacturer, could that have worked loose? Is the pump old enough to have worn?

Obviously without seeing your specific engine one can only guess but if you have changed filters and bled air and it is still down on power I would start with the simplest things such as: Has the throttle lever stop screw worked loose and stopping the lever moving fully. Then move on to cylinder compression, then injector pop pressure and spray pattern, then governor set up , then pump set up.
 
If you cant get it sorted out and have to get a Mechanic find out if there is a Tractor dealer near you who has a mobile mechanic service. Mechanics who work on Tractors are working on Perkins engines on a daily basis and the 4107/8 was fitted in a Massey Ferguson MF 35. The 4235 in a MF 165. And even my 10 ton Road Roller had a Perkins in it. Also a cheap source of parts.
 
Yes. Had them tested and they sent them back.
Don't get any hunting.
I do not believe there is any way that timing could have changed as the pump has not been removed.
I will check the max speed screw, but this probably isnt the problem as when on full load - increasing the throttle starts to chuck out unburnt fuel.
Definitely not the throttle lever.
Guess I need to look at the compression

Thanks

Stephen
 
Billjratt said:
Check the exhaust for partial blockage. Probably the area where the cooling seawater is injected is prime suspect. Also check rubber hose as it may have delaminated and be horrible inside even if it looks OK from outside.
Click to expand...

Still a good idea to check the rubber exhaust if you have not yet because these do collapse internally and act almost like a flap valve causing back pressure & limiting the revs when under load as the quantity of exhaust gas cannot escape. Usually as a result of overheating if the water feed gets very low or even stops because of an intake blockage or impeller failure. Many people have been caught out & spent an awful lot of money before finding this was the problem.

John Lilley
 
When I had the same problem with my 4108 it was a problem with an open crack in the fuel lines letting in air when under load, it was fine on tick over but as soon as we tried to increase the load nothing much happened. New fuel lines from the tank sorted it for about £150.
 
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