thanks for the input. i bypassed the lift
pump with an electric fuel pump
and unfortunately saw no improvement. but it sure makes it much easier to bleed the system now.
i guess i need to go back to the beginning to try and figure out my problem.
this is on an md6a in a 9000lb sailboat 29.5 ft long. boat is a recent acquisition so hard to compare performance to the past. on sea trial and shake down cruise
engine performed as expected. full throttle in gear
gave about 2300rpm negligible smoke no overheating
. full throttle in neutral gave just north of 2400 rpm
. prop is year old 3 blade
12x12. i am not much of a motor
sailor and primarily only use the engine in marinas
, restricted areas and approaching my mooring
ball. knowing the previous owner used the engine even less than I, i added some seafoam to the tank on the last fill with the though that the system would get a good cleaning
the next time i took her out. while transiting from the fuel dock
back to the mooring
i was running her close to full throttle 21-2200rpm all was good. then the rpms dropped, i thought the engine was dying but before i could throttle down or shut down the rpms stabilized just over 1500. no black smoke, engine sounded "normal" i pulled back the throttle till it started to reduce rpm and then set it right at 1500 i then popped the hatch
to check out the engine. all seamed well no evidence of over heating
of any kind. i was close to my mooring so i continued on and secured her till my return as i was needing to catch a ferry
home. the engine at idle as i was shutting down did not seam as smooth as it had previously but i had only run it a half dozen times or so, so it could have been a mis perception. on my next visit she started just fine and idle like when i had shut her down. she would rev up to 2400 in neutral but still only around 1600 in gear
. while reving in neutral it seamed to really smooth out around 1800-2000rpm everyone that heard the engine said she sounded real good but i still felt she was stumbling somewhat at idle and lower rpms both in gear and neutral.
my initial thought with reduced performance and negligible smoke i figured fuel starvation as the problem. with my recent seafoam treatment i suspected i had loosened a bunch of gudge and the filters were plugged. after talking with the old owner he mentioned having recently changed the aftermarket racor
but commented it had been a long time since he had changed the engine mounted filter or screen
on the lift pump. so i replaced the engine fuel filter
and restarted the engine and found no noticeable change. idle sounded the same full rpms in neutral and 1600rpm full throttle tring to tow the mooring. so i shut it down and went to replace the aftermarket racor
. as i attacked the racor i noticed the drain cock on the bottom and decided to drain a small amount from the bottom to see if i could see water
or other contaminants. to my surprise, instead of fuel dribbling out it sucked a bunch of air bubbles in through the filter housing. this led me to think the racor was blocked and the pump had pulled a vacuum on the fuel line. so i swapped out the racor element and the old filter paper was effeminately dark almost black compared to the amber colored paper on the replacement element. i was feeling pretty confident i had solved
my problem and fired up the engine again only to have the same performance. so i decided i would go ahead and motor in from the mooring to the local dock
before i continued only to find i had not bled the system sufficiently and the engine died just as i drifted off the mooring. i threw the sails
up quickly but the was really no wind
and what little there was kept shifting around. i was doing my best to navigate the mine field i mean mooring field when a nearby boat started chatting me up. i guess i must have looked like i had it under control...lol after a few exchanges i asked explained what happened and asked if his dighy had enough umpf to pull me back to my mooring a 100ft away or so. after the adventure of him wanting to drag me backwards "cause we are so close" and me not arguing with free help i got her back on the mooring. at this point i knew i had not bled the system enough and proceeded to get that right. after that and another chat with the old owner i decided to replace all the rubber fuel lines as they were approaching 10yrs old. i replaced all the lines from the tank to the engine and back to the tank. still no joy, then after posting
here i bypassed the lift pump with an electric still no joy.
when i bought the boat i knew of the problem with fuel in the oil and expected to deal with that . old owner suspected the injection pump but i was of course hoping it was the lift pump. the injection pump had been rebuilt 10 or 15 years back but we could find no mention of replacing or rebuilding the lift pump in the maintenance
records. old owner commented on having tried biodiesle sometime in the past and wondered if that could have caused the leak allowing fuel into the engine oil. i am kinda hoping the leak was in the lift pump and that by bypassing it i have solved
that problem. i will be changing oil on my next visit and continuing to try to get back to full power.
i have read and reread the owners and shop manual for the engine and every post i could find here and elsewhere on the net about the md6/7a with similar problems. i have suspected and not addressed the possibility i picked up something on the prop. i will be diving
the bottom to check that out next, fingers crossed. i have also heard of similar performance hits due to plugged exhaust
particularly at the water
( engine is fresh water cooled) old owner had pointed out prior to sale
that the elbow
had not been replaced in a while and he suspected it would be due in the near future. other aspects i suspect are the injectors themselves and the injection pump. i have extensive mechanical background but not much in the realm of diesel engines. had a VW diesel car for a while and a pair of detriot 353's but never had a problem with em. i am wondering if the injection pump can fail in such a fashion that it "works right" just not deliver enough fuel under load. i do imagine a bad spray pattern from the injectors would certainly reduce output but would that lead to "black smoke" ? i would also think a fouled prop would give black smoke as well?
whew, that was long winded and a messy run on for sure but i hopefully covered all the bases.
if anyone has suggestions or thoughts on how to proceed i would love to here them. simple and cheep first is my motto so diving
in and inspecting the prop is first. then i guess i will pull and inspect the exhaust
injection elbow followed by pulling the injectors and the the injection pump if nothing else proves fruitful.
thanks in advance for assistance in reviving my old md6a