Isuzu misfire

[Captain_Badger]

Since the summer my engine has developed a misfire. Isuzu 35, prm120 gearbox. Engine 1900 hours, gearbox 400. Engine starts well, but only when cold and usually in forward gear splutters and seems to hold back momentarily. Sometimes causes gearbox to not engage. Fine after ten minutes cruising. I am about 10 hours after adding correct quantity of Miller oil injector cleaner to the tank. Pretty sure it is injectors, but before I rip them out, anyone got any ideas please? Thanks

[mrsmelly]

12 minutes ago, Captain_Badger said:

Since the summer my engine has developed a misfire. Isuzu 35, prm120 gearbox. Engine 1900 hours, gearbox 400. Engine starts well, but only when cold and usually in forward gear splutters and seems to hold back momentarily. Sometimes causes gearbox to not engage. Fine after ten minutes cruising. I am about 10 hours after adding correct quantity of Miller oil injector cleaner to the tank. Pretty sure it is injectors, but before I rip them out, anyone got any ideas please? Thanks

I am not a mechanic but in my experience especialy with a brand new engine like that its usualy some fuel blockage/manky fuel filter. The engine has done no hours so I cant see what else could have any wear to cause those sypmtons unless its been stood for months on end?

[Captain_Badger]

Engine time spread over 11 years and oil/ filters serviced like clockwork every year. I was getting black soot on accelerating but that seems to have got better since the injector cleaner. As I said, behaves nicely once warmed up.

[mrsmelly]

6 minutes ago, Captain_Badger said:

Engine time spread over 11 years and oil/ filters serviced like clockwork every year. I was getting black soot on accelerating but that seems to have got better since the injector cleaner. As I said, behaves nicely once warmed up.

Someone who knows properly will be along soon with proper advice. For me though lack of use is what knackers most aspect of boats as being stood idle does nowt much good. 1900 hours is the square root of bugger all in eleven years and the engine probably spends most of its time being started and getting up to temperature which it will not like. As a for instance a hire fleet Beta with 10 thousand on runs like brand new and a boat I skippered on the Trent with 35k hours still runs spot on.

[Captain_Badger]

Get what you are saying, but once started, rarely does less than a couple of hours of work so should be warmed through properly. 

[cuthound]

Is it using any coolant?

A slight head gasket leak can cause a misfire after starting until the coolant in the cylinder has evaporated.

Edited November 25, 2017 by cuthound
Spillung

[ditchcrawler]

I would say air. after running for 10 minuets its all cleared. Probably wrong though

 

[Captain_Badger]

Always make sure it has coolant. Yes, properly anti freezed and doesn't seem to use any water.

Edited November 25, 2017 by Captain_Badger

[Bod]

When were the fuel filters last changed?

 

Bod

[Captain_Badger]

Fuel filter changed April. Was clean as a whistle. Done about 60 hrs since

[Bod]

Was the problem there before the fuel filter was changed?

 

Bod

[Wrinkley]

Find a river and give it some stick.  If its going to clear that will do it.  If it does not get the injectors checked.  Well that's what I would do.

[Captain_Badger]

Been giving it some up to around 12 to 1300 rpm for an hour at a time. My gut feeling is a blocked injector. It was so sooty before, can't imagine that some of it didn't stick. Usually pretty gentle with it. Never much above 1100 rpm and rarely any river work. Not a huge job to whip out the injectors and take them to Cheltenham diesels. Just wanted some confidence that I was barking up the right tree.

[ditchcrawler]

6 minutes ago, Captain_Badger said:

Been giving it some up to around 12 to 1300 rpm for an hour at a time. My gut feeling is a blocked injector. It was so sooty before, can't imagine that some of it didn't stick. Usually pretty gentle with it. Never much above 1100 rpm and rarely any river work. Not a huge job to whip out the injectors and take them to Cheltenham diesels. Just wanted some confidence that I was barking up the right tree.

What about what Bod said?

[Wrinkley]

Guess you know the problem, Remove injector get them checked. If nothing else it will eliminate them as the problem

 

[Captain_Badger]

Just looked at the log. Problem seemed to start about 60 hours after fuel filter change. It was next morning start up after long descent of Tardebigge. Filter always seems clean when I change it. Might add that the misfire happens only under load when cold.

[mrsmelly]

14 minutes ago, Captain_Badger said:

Been giving it some up to around 12 to 1300 rpm for an hour at a time. My gut feeling is a blocked injector. It was so sooty before, can't imagine that some of it didn't stick. Usually pretty gentle with it. Never much above 1100 rpm and rarely any river work. Not a huge job to whip out the injectors and take them to Cheltenham diesels. Just wanted some confidence that I was barking up the right tree.

Yes its sounding more like under use. Diesels like to be thrashed and at those revs and those hours over such a long time you have miffed it. Give it some what for and if you are going to Cheltenham diesels you may well live over that way and you can take the boat onto the severn and give it some what for

[Eeyore]

Definetly needs a good trashing. Coolant temperature is no indicator of combustion temperature. An exhaust gas temperature in the range 1000 to 1200 degrees Fahrenheit is concidered "healthy".  As an apprentice I was surprised how quickly carbon built up the injectors (we had half a dozen Perkins 3.354 that ran for 30 min between top end overhauls!)

[Captain_Badger]

Ok, thanks all. I think I see a way forward.