Mercruiser 2.8 D-Tronic Rev Problems

[salar]

Hi all, I have read some very informative posts on Mercruisers here so I hope someone can help with my problem. I have a diesel Mercruiser on a Trophy sportfisher which has run perfectly for 5 years. Last season I had occasional problems when it would drop revs from cruising speed (3,000 down to 2,500) then climb back again. This would happen a couple of times a trip, irritating but not really a problem. This season the problem has got progessively worse and last trip it would not rev beyound 2,500 at all, when it did it would drop back then climb up again only to drop back again. My local engineer is perplexed. We have changed the primary fuel filter in case there was muck or bug, it is clean. My next step is to call in the guys with computers but that will be expensive and the local engineer is not convinced that will find the problem. Has anyone else has this problem with a Mercruiser? Is there any other fault-finding I should do? Thanks in anticipation...

 

[spannerman]

I would check the fuel system thoroughly from tank to motor to be 100% sure no air is getting in, a quick check to eliminate the boats plumbing is to run the engine from a 5 lt can of diesel with 2 short lengths of hose to the pump and return. If it still does it then you know the problem is on the engine itself, I would then check the lift pump as I have had these leak air into the system before.

 

[salar]

Thanks for the quick reply - do you think it is more likely to be a fuel supply problem than an engine management problem (e.g. faulty sender somewhere)?

 

[salar]

Update on Mercruiser 2.8 D-Tronic Rev Problems

I carried out another sea trial this morning after the fuel system had been cleaned. It cruises fine at 2,800 but if the revs are increased to 3000, after 15 to 20 seconds it drops back to 2,500 then climbs back up (by itself) to 3,000 for another 20 seconds or so before repeating the cycle. At one point it held 3,000 for several minutes so if it was a fuel problem surely that would not have happened?

 

[DAKA]

Re: Update on Mercruiser 2.8 D-Tronic Rev Problems

as you have restricted your post to a specific engine there will not be a huge input of replies as Mercruisers (touch wood) are generally reliable.

There have been several reports on here about fuel pick up pipes being blocked which can happen to all makes of boats/engines.

The symptoms you describe would indeed back up this guess.
There could be something blocking your pick up that is swashing around in your tank.
Another guess would be the tank breather is blocked with spiders webs and salt, tooth brush and water to clean gauze or run with the filler cap off.

You can gets loads of guesses and waste a season going through them or you can follow a process of elimination directed by someone who knows what they are doing.

I would check the fuel system thoroughly from tank to motor to be 100% sure no air is getting in, a quick check to eliminate the boats plumbing is to run the engine from a 5 lt can of diesel with 2 short lengths of hose to the pump and return. If it still does it then you know the problem is on the engine itself, I would then check the lift pump as I have had these leak air into the system before.

 

[salar]

Re: Update on Mercruiser 2.8 D-Tronic Rev Problems

Thanks, I did wonder about the tank obstruction because it is so random, and the engine picks up as soon as the fuel flow drops. It looks like the next step will be to try the fuel can idea.

 

[salar]

Re: Update on Mercruiser 2.8 D-Tronic Rev Problems

Thanks for the advice, I finally managed to do a test today as you recommended with a separate tank, and it ran fine. It must be the fuel tank! Took the tank tube out and...the gauze was packed with swarf. Cleaned up, another sea trial and she runs perfectly.