Mercruiser 3.6 diesel

Converging

Converging

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Hi everyone, I am still working through the issues with my 1996 Sealine 330 Statesman!! (I thought boating was supposed to be relaxing).

The engines are 3.6 Mercruiser diesels.

Latest issue is I have one engine (Port) refusing to go up to full revs. She is down by about 500rpm during a sea trial.

I have changed the diesel hoses.
I have checked the turbo is spinning
Changed the diesel filters
Changed the air filter
Checked the cables are pilling the throttle to max.

I notice tha the throttles do have a limit stop should I try to back this off or leave well alone?

Can I safely run them upto 3800 rpm in neutral when moored? This is the only thing I haven't tried.

If they do go up to 3800 rpm what do I try next??

There is one little issue with this engine which is a slight oil leak but to date I cannot find were it is comming from.

Thanks guys.
 
Just checking the manual there is no wastegate on your engine so i would check the manifold for air leaks. The injectors are self priming but it may well be good to crack them open with the engine running to bleed them. Also try changing over the fuel selector tap.
 
Manifold

Thanks for this advise but I am still a bit new to this. How would I check the manifold for leaks. Did you also mean completly replace the fuel selector tap?
Could it be that I have an injector down and if so how would I check this?
Sorry to be a knob but I am a petrolhead and these diesels are a whole new ball game for me!!!
 
i'd start by getting a digital rev counter to shine on the flywheel. Are you sure they're different revs?

Then check:

tappets
injectors (take them out and a specialist can refurb/adjust if they are out of spec)
check diesel timing

I do far more boat/engine jobs myself than mr average, but for at least 2 and 3 above, I'd ring Col of this forum. Actually I did.......
 
Col's based in reading, pm him and ask. Cardiff not much further than Chichester from there, and he works there.

taking the injectors out not too difficult, if you can find a local diesel specialist to check the pattern/adjust/refurb as neccessary. Col has the machine to check the pattern then he just takes duff ones if but you could take them all. There used to be one in Ninian Park Rd I used when I lived there but that was a while ago.......

Apparently merc injectors often need adjusting after 1000 hours. (i'm on 1100 and odd and mine needed doing)

pm if you need a scan of the relevant pages of the workshop manual.
 
Getting closer!!!

Went down to the boat at the weekend and can now up date as follows:

The engine that is down on power freely revs when not under load with no hesitation within the rev range and hits the maximum rev limit with no problem at all.

Cracked each injector briefly and there was a noticeable drop on each cylinder.

I then did the same operation again with a view to bleeding the injectors.

Took her out for a spin and had gained another 300 RPM

Noticeably the engine that was down on revs lagged well behind the correctly running motor and took around a further 20 seconds to get up to the improved rev limit.

Any suggestions? I am strongly leaning towards having the injectors serviced.
 
Converging said:
Went down to the boat at the weekend and can now up date as follows:

The engine that is down on power freely revs when not under load with no hesitation within the rev range and hits the maximum rev limit with no problem at all.

Cracked each injector briefly and there was a noticeable drop on each cylinder.

I then did the same operation again with a view to bleeding the injectors.

Took her out for a spin and had gained another 300 RPM

Noticeably the engine that was down on revs lagged well behind the correctly running motor and took around a further 20 seconds to get up to the improved rev limit.

Any suggestions? I am strongly leaning towards having the injectors serviced.
Click to expand...

Definitely have the injectors checked IMHO. How many hours on the engines? As I said before they are known for needing an injector service at 1000ish
 
Converging said:
Went down to the boat at the weekend and can now up date as follows:

The engine that is down on power freely revs when not under load with no hesitation within the rev range and hits the maximum rev limit with no problem at all.

Cracked each injector briefly and there was a noticeable drop on each cylinder.

I then did the same operation again with a view to bleeding the injectors.

Took her out for a spin and had gained another 300 RPM

Noticeably the engine that was down on revs lagged well behind the correctly running motor and took around a further 20 seconds to get up to the improved rev limit.

Any suggestions? I am strongly leaning towards having the injectors serviced.
Click to expand...

I would think that injectors would perhaps manifest in a no load situation as well as under load. Assuming the fuel and air supply is not restricted, ie filters, it could be any one or a combination of issues, governor, compression, turbo, crack, leak etc etc, I hate to sound defeatist but you could spend money on injectors and trying different remedies, in short time for an expert. At the moment your engine is at its simplest to diagnose if you keep "trying" remedies you may hide the real issue, perhaps akin to taking the back of your television.
 
The boat is a 1996 but has only run 400 hours. This is what makes me suspect the injectors. 13 years of little use must have taken its toll. I am ruling out compression issues as the drop off in revs was equal on all the cylinders when i bled each unit.
Reving under no load would also be cosistent with wrong fuel atomisation - Or would it???
I take on board the advice in calling in an expert but I really want to see this through and I have already made progress with help from this forum. (Thanks to everyone - but keep the suggestions comming - PLEASE:rolleyes:!!)
 
Considering the relative lack of use and the nature of how boat engines seem to spend their lives then having the injectors cleaned would not do any harm anyway and personally i'd say it should be part of the service schedule in 14 years use.

Back to diagnosing the problem, id say you need two bits of information for an accurate diagnosis. One is an accurate rev measurement on both engines to ensure they are both running what the guages are saying. However i'm sure you will be able to feel the response difference between the two.

Secondly i'd say you need to be able to measure the Boost Pressure the turbo's are running on each engine.(under load)
My guess (and it is a guess) is that one engine is running lower boost than the other. Possibly because of an air leak somewhere on the pressurised side of the intake system.

Boost leaks don't tend to manifest themselves in 'neutral' as they're not running under load and hence running minimal pressure. (This is from Petrol Turbo engines so i'm assuming the principals remain the same on diesels).
This is why the engines will rev out in neutral and not show any problems.

Also a basic compression test of the engines wouldn't go a miss at this stage either.
 
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