SMoking Diesels

[stewart]

Now my knowledge of diesels is limited but this confuses me...


I have 2 x 550 HP Detroit Diesels one of which is down on power substantially and smoke when above tickover, even with no load. I've had injectors and turbos replaced but now the engineers seem confused (it would help if they spoke any English or me Spanish!). So what are possible causes? My logic goes like this:

Smoke is balck and sooty so it can't be from oil (that would be blue).
Black smoke suggests that the engine is running too rich and that must mean something needs adjusting.

As far as I can work out the engineers think that there is a fuel blockage but surely this would mean it running lean?

Any thoughts on possible causes?

Thanks

Stewart

 

[Nauti Fox]

Give Alf (Divemaster 1) a pm, he's got Detroits and is pretty knowledgable on them.

 

[LeytonC]

Black soot is can be caused by not enough air for the amount of fuel injected, i assume you have checked air filters and that enough air can get to the engine room.

I had a smoky port engine, this was caused by the cylinder head choked with carbon and not letting it breath properly.

I assume your fuel is the clean and is the right grade.

 

[Divemaster1]

These wonderful two-strokes are great and rewarding engines to work on when you get it right, but when not, they get confusing...

Get back to basics.... and presume that these are V6's or V8's and perhaps even V8/93's

in no particular order....

these ones should be easy to sort out ... just take it step-by-step ....

1) Do you get full RPM at no load? (should be carrying a stamp on the rocker cover with load/no load rating)
2) Have you had the fuel rack set ? a bit of a knack to that one on the V's, but simple procedure, as long as you do things in the right order.
3) Is the air filter clean
4) Are you sure that you have injectors of the same rating in all cylinders (stamp on each of the injectors on the base ... sort of between the fuel inlet and return) easy to check by removing rocker covers.
5) do you get enough air into the lumps
6) How many hours do you have on the clock
7) Presume you do not get full RPM with load
8) What's your prop rating .... if overpropped you may have some more problems calling for big bill.... check with SS what the boat should have been delivered with
9) fuel filters replaced?
10) is compression OK and is piston rings checked (can be easily done in situ)
11) is the blowers checked

Did they really change out all injectors ??? Hope not, as they should have been individually tested and I would have been surprised to see more than 30% replacements. And presume that you got refunds for the bases ... replacement injectors should be in the region of £55 each....

did they really have to change the turbos ??? these have an approximate design life of 10,000 hours, but in a MOBO they do tend to kill themself standing..

Will stop there until you have some more answers....

 

[stewart]

Thanks, that's all great stuff...situation is that the (supposed!) DD specialist in my part of Spain is doing the work not me, but he seems confused too and not sure how good he is. Engines have been serviced and all filters replaced etc and the problem happens in neutral so can't be props etc. apparently the pressure on the engine side of the fuel pump should be about 1.5 and on the bad engine it's 4.0...all injectors and turbos have been replaced as part of the "so called" cure but it didn't sort the problem. The engines are the V6 from a 1991 Sunseeker. It does seem to get full rpm at no load but lots of black smoke...compression problems wouldn't cause this would it?

It does seem to be a fuel system problem given the pressure difference but they've been right through the system and can't find a blockage. I can't imagine a faulty fuel pump generating too much pressure but it would explain everything...is this possible?

Thanks is advance.

 

[Divemaster1]

1st thing first.

After fuel injector change, you need to set the fuel rack ... with the idle screw fully backed off (otherwise the injectors will be out of sync).
then set the idle, etc ... governor can be a right pain.
Once that is done you can do the rest of the fuel system ... and yes the man pump could be a poblem, but finally it is the injectors on these engines that deliver the ammount of fuel into combustion chamber ... each injector is a small pump in itself that needs to be set in synch with the others ... otherwise it ain't gonna work right.
A knack to this as I said and a definete order to do things ... no electronics here ... just a lot of moving parts that needs to work in sync.
Ask them abou the fuel rack setup and you'll get a feeling if they know what they are doing ... otherwise find someone with the DD 2 stroke knowledge... Please let me know if you want me to try to find someone ... where are you bertherd??

 

[stewart]

Thanks. I'm in Ibiza and the guys are supposed to be DD specialists...at least that's what's painted on their van! Explaining anything is a problem as they have no English and my Spanish is less than useful outside a restaurant...on a good day we can just about manage to point at things and agree what time they will turn up (that's another story though!). Current theory is dirty intercooler may not be allowing enough air through so that's been out and is going back in as we speak. Doesn't explain the difference in pressure in the fuel systems though...

 

[Divemaster1]

Ok .... Air system on these have a couple of potential "bottlenecks".

1) air filter ... a bit touchy on these, as they do require more air than your "normal" 4 - stroke, firing on every 2nd stroke.
2) Turbocharger ... not strighly needed at low revs, but once kicking in, it generates additional pressure in the air chamber (after the blower)
3) Connection hose between Turbocharger and intercooler (approx 2" with clamps ... normally thin, multi layer, very strong and heat resistant... prone to leaking, and may crack ... however you would see "black" streaks around this area if leaking .... minor leaks here may result in RPM drop of 100.
4) not sure if intercooler is a problem, but can be "gummed up", so cleaning cannot be negative.
5) Connection hose between intercooler and blower ... See 3 above
6) Blower ... (Big Bill item). This one may cause some problems, and is in integral part on how these engines gets the power vs others... this forces air into the air chamber and maintains the pressure when the "scavenger ports" opens up and forces new air into the combustion chamber when the piston is low down... (New air also forces exhaust gases out the exhaust valves .... no air intake valves on these engines, leaving new air in the chamber for the next stroke, which also is a combustion stroke ... hence 2 stroke).

Blower is normally a "no touch" item as it is extremely reliable, but may need servicing every now and then.... but normally not unless you are doing a re-build ... 1500 - 3000 hours perhaps ... depending on which load you have on the engines. Besides that, if there were any issues with the blower, I'd expect you to hear this easily ... (blower is situated between the V, as a cylindrical item after the intercooler.

Keep us informed about the intercooler cleanup and let us know what's happening ... just sounds strange that both engines are doing the same.... .. have you checked out the fuel system from tanks to fuel pumps ??