Need help with diagnostics please . . .

[L'eau.Life]

Hi guys,
I have twin marinised Nissan QD32 normally aspirated 4 cyl motors.
Stbd motor pulls 3600+ but port has deteriorated down to 3000 max RPM @ WOT. Engine starts and runs sweet but uses twice the fuel as the Stbd. Evidence of white smoke underway.
Have so far chem-cleaned pod air filter, changed all fuel filters and cleaned non-return valves at the filter priming pump. Removed injectors and pump and had these overhauled by Garrett who also set the engine timing and adjusted valves etc.
High fuel use vs white smoke seems to be contradictory but I am no diesel mechanic so looking for ideas please.
Thanks in advance, Alan

 

[NavalSArtichoke]

White smoke in the exhaust is a potentially bad sign. I would check the compression on this motor, because white smoke is one indication of a blown head gasket. Also check the lube oil to see if there is any water contamination. With a blown gasket, that would also explain why it doesn't rev and the fuel consumption is up.

 

[L'eau.Life]

Thanks NavalSArtichoke - plan to run a compression test Tuesday and will report back but no evidence of oil in coolant.

 

[PAR]

White smoke is evidence of water vaporizing in the exhaust stream. Blue smoke is oil burning, so be clear about the color - is it white or light blue? It's possible to have a cracked head, manifold or even a burned head gasket, without water getting into the oil or oil getting into coolant passages.

 

[CDK]

Stbd motor pulls 3600+ but port has deteriorated down to 3000 max RPM @ WOT. Engine starts and runs sweet but uses twice the fuel as the Stbd. Evidence of white smoke underway.

This is contradictory information.
With less rpm and twice the fuel consumption the engine must be bellowing black smoke due to incomplete combustion.

Long distance diagnosis is often wrong; I'd put my money on a fouled stbd prop, possibly damaged or with something wrapped around it. The engine spins to 3600+ but leaves the hard work to its companion.

 

[L'eau.Life]

@CDK
Interesting approach but changing Stbd power setting has marked impact on performance - run both at 3000 pulls about 12kt, open Stbd to 3600 and speed increases to around 15kt. Will try to dive and check both props again in the morning but pretty sure this is a problem with the port motor.
Thanks! Alan

@PAR
Hopefully compression test on Tuesday will give me some more clarity. Smoke is definitely white and looks more like steam than actual smoke.
No water in oil or v/v and no residue in sea where exhaust discharges.
Thanks! Alan

 

[gonzo]

Also, light grey smoke is from oil burning. If it has a wet exhaust, it is often very hard to tell.

 

[WestVanHan]

As with CDK, my first thought was to check the props.
And then the items you have done. Other than that it could be low compression from a stuck ring,or any of the ideas as above.
let us know...

 

[L'eau.Life]

Dived to check both props today and no fouling so further engine investigation to happen during the upcoming week. Will definitely report back with findings but meanwhile; thanks to all for the advice to date.
Cheers, Alan

 

[PAR]

A bad prop isn't likely going to produce white smoke. Water is getting vaporized somewhere.

 

[WestVanHan]

White smoke is caused by raw unburnt fuel,from low compression (rings.valves,bad timing) and in the case of a fouled prop overloading the one engine-I know this from personal experience.

As well as water of course,but it's easier and costs nothing to check the props first...

 

[french44]

Hi , do you have any indication of the temp (water /oil) and pressure (oil). What is the RPM without load of the both engines (void test) ? do you change the config of air inlet circuit for this engine (position of inlet, pipe etc....) ?

 

[powerabout]

white smoke can also be no combustion, like the nozzle has fallen off an injector?

 

[L'eau.Life]

@french44
Water/oil gauges show the same for both engines. Have not checked RPM without load - not sure about running them like that . . . No change to air inlet

@powerabout
Injectors and pump overhauled by Garrett thanks

Compression test scheduled this morning

 

[mike Banks]

White smoke

I have had a similar thing happen to a tractor. Check the exhaust for blockage. Excess back pressure means insufficient air getting into the cylinders--and excess fuel usage.