Sheppy
Well-Known Member
I'm fielding this out as I really don't know enough and am on a fact finding mission. Last weekend I had some engine problems with my Mercruiser 1998 D-Tronic 165 engine. After what seemed like a good start in the afternoon, the revs started dropping about ten minutes into the run, they would slowly drop from about 3000 to about 2500 then they'd surge back on again. This continued for some time, it almost felt like the turbo was just dropping out, then running up again. However the revs did eventually drop quite low and I only just managed to limp into port on idle.
I was fairly low on fuel, although not on reserve and I didn't have any water in the separator.
It felt very much like a fuel shortage and so thought perhaps a blockage in the pipes, filter or just dirty fuel. The following morning, I tried blowing back up the fuel line into the tank but I'm not sure I created enough pressure. I replaced the fuel filter/water separator, although it looked perfectly ok, and added 40 litres of good fresh fuel. She then ran on idle well and after letting her run gently at 2000 rpm for a little while, decided to take her on a run. She seemed fine up to 3200 rpm but if I pushed higher she would start to falter and fall off the revs, but I could at least coax her back up to about 3200 where she'd stay. She ran at 3200 for good twenty minutes.
After a few hours rest I tried again but she failed to get above 3000 and just kept dropping off the revs again. I came back in at 2000 rpm where she seemed fine. The following morning, I did a four mile run at 3100/3200 to fuel up, added a 100 fresh litres and from that point she seemed to run ok expect now she fails to get much over 3250 rpm, although at least she wasn't faltering anymore.
Now I don't like revving an engine in neutral but I did blip her to 3800, not hesitation at all. So it's certainly a loading, fuel or air issue.
One thing I haven’t got is a pre filter prior to the filter on the engine, I know, I know. Can someone recommend a reasonably priced pre filter with a visual water bowl, ideally sub £100, and what micron filter?
One other thing I did notice, my prop on my bravo x 2 leg turns in neutral but not without a little resistance. I must admit, I would have thought there would have been virtually no resistance at all? And I can't see anything around the prop. Is this normal or could this be the problem?
My next test will be to eliminate the tank and fuel lines but running her on a temp set-up, again with fresh fuel. Other than that, I'm looking for ideas to explore like a collapsed turbo pipe or faulty filter seal, although those aren't currently high on my list suspects.
Any help and advice will be gratefully received.
I was fairly low on fuel, although not on reserve and I didn't have any water in the separator.
It felt very much like a fuel shortage and so thought perhaps a blockage in the pipes, filter or just dirty fuel. The following morning, I tried blowing back up the fuel line into the tank but I'm not sure I created enough pressure. I replaced the fuel filter/water separator, although it looked perfectly ok, and added 40 litres of good fresh fuel. She then ran on idle well and after letting her run gently at 2000 rpm for a little while, decided to take her on a run. She seemed fine up to 3200 rpm but if I pushed higher she would start to falter and fall off the revs, but I could at least coax her back up to about 3200 where she'd stay. She ran at 3200 for good twenty minutes.
After a few hours rest I tried again but she failed to get above 3000 and just kept dropping off the revs again. I came back in at 2000 rpm where she seemed fine. The following morning, I did a four mile run at 3100/3200 to fuel up, added a 100 fresh litres and from that point she seemed to run ok expect now she fails to get much over 3250 rpm, although at least she wasn't faltering anymore.
Now I don't like revving an engine in neutral but I did blip her to 3800, not hesitation at all. So it's certainly a loading, fuel or air issue.
One thing I haven’t got is a pre filter prior to the filter on the engine, I know, I know. Can someone recommend a reasonably priced pre filter with a visual water bowl, ideally sub £100, and what micron filter?
One other thing I did notice, my prop on my bravo x 2 leg turns in neutral but not without a little resistance. I must admit, I would have thought there would have been virtually no resistance at all? And I can't see anything around the prop. Is this normal or could this be the problem?
My next test will be to eliminate the tank and fuel lines but running her on a temp set-up, again with fresh fuel. Other than that, I'm looking for ideas to explore like a collapsed turbo pipe or faulty filter seal, although those aren't currently high on my list suspects.
Any help and advice will be gratefully received.
