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SeaBreeze-1 · 29-05-2017, 07:08

I have to agree with some other posters regarding the possibility of air in the system as the same problem happened with me. My old Yanmar doesn't have glow plugs so can't blame it on them.

I first noticed late last year that some of my starts were a bit on the rough side until I gave it a little extra throttle. The engine would then settle down to where it was supposed to be. This spring, immediately after launch, the boat stalled in the harbour and refused to start again (I did do a prelaunch start/run before going in the water). After getting towed to the seawall, I did the usual stuff checking from the fuel pump all the way to the injectors. Pre filter checks didn't reveal any problems but when I cracked open the injector feed lines, I discovered one of them wasn't feeding fuel.

The problem ended up being air in the system, some in the small engine mounted fuel filter and also in the injector pump. Once I bled those everything came back to normal and my engine starts are now nice and smooth.

You indicate that your boat has been sitting for several months. That's the identical scenario that I had. Hope this helps.

Dave22q · 29-05-2017, 07:27

OP suggests problem solved by giving some extra fuel and/or restarting. Seems to me that investing time and money looking for 'fixes' makes no sense. There are too many real problems that do need fixing. "
If it ain't broke..." !!!

gjordan · 29-05-2017, 08:21

I have a suggestion for this and later trouble shooting. Buy one of the low cost hand held infrared thermometers. Do the glow plug warm up for the engine, but dont hit start. Immediately check the glow plugs, and it will tell you if one is not heating. If they are all even temp, then start the engine (rough running condition) and start checking the injector temps. Go back and forth along them all and the comparison should soon tell you which cylinder is not running. If you know which cylinder is dead, it cuts down on changing perfectly good parts on good running cylinders. Your present problem could be glow plug, injector, low compression, hair-line crack in a fuel line, etc. It is a very handy, low cost tool to have in your kit. Good Luck, ______Grant.

Cheechako · 29-05-2017, 08:35

Because it sat in the yard for 7 months, I'm suspecting debris of slight corrosion on an injector tip. Have the injectors serviced maybe.
I don't know the Mitsu engine, but it seems to me not cold enough in So Africa to even need glo plugs. I've not used glo plugs on any diesels in 40 years. Even up here in the PNW.

donradcliffe · 29-05-2017, 09:10

Its a fairly normal thing for elderly diesels--one or two cylinders aren't firing until they heat up or the revs go up. It can be dodgy injectors or low compression.

https://www.youtube.com/watch?v=ZXFQm07SsYI

Your diesel isn't very elderly at 1500 hours, and its got a lot of starts left in it before you have to warm it with a torch or spray WD40 in the intake to get it to start. You can probably ignore the problem for several years until it gets worse.

OR, You can work on isolating the problem cylinder by cracking all the injector lines when cold, then tightening them one by one as someone cranks the engine over. The cylinders that fire when you tighten them are good, the others are the problem. Don't forget to shut off the engine cooling thruhull when doing extended cranking, and opening it when the engine starts.

OR, you can call a mechanic and write a check.

Captain Bob · 29-05-2017, 14:43

Air leak unlikely but possible if the engine runs and idles fine after the first start up, I suspect either old (read bad) fuel, poor compression (valves) or an injector problem. Injectors should be rebuilt/ replaces after 12 - 15K hours and the valve clearance should be checked/adjusted every 500 hours. I would check fuel condition first, valves second and injection system last.

rognvald · 30-05-2017, 16:37

Quote:

Originally Posted by Iaangus

It could be a few things, You mentioned filters were changed, if there is a leak anywhere in the fuel supply line including a filter it can allow air to enter the system. if a few drops leak out somewhere a little bit of air can be sucked in at the injector. This air at the fuel atomizer / injector act a a cushion for each pulse of fuel. At idle the tiny pulse of fuel is not large enough to overcome the cushion of air. when you give it more throttle the puse of fuel is larger and faster and purges the air. The same problem can also arise with a bad injector allowing leakage. Another possibility resulting in same symptoms could be a faulty check valve usually mounted near where fuel enters the filter is allowing fuel to drain back to the tank when engine is shut off for a considerable time. again air is drawn in through the injectors to replace fuel draining back to the tank. This usually only happens when fuel level is lower than the filter level. Another possibility is that the fuel shut off wether mechanical or electrical is not returning to run position when it should be. If your engine shuts off when you turn a key off it is an electrical shut off. They are usually all or none. A pull knob, (maybe they are not even used in a marine engine) would be mechanical. With a mechanical shut off they need to be adjusted to return to start position when the knob is pushed in. These are all easy fixes, hopefully one of these fixes your problem.

Great response, Iaangus! We had the exact problem when our injection pump check valve was bad and leaked fuel back after sitting. If you've never had your pump tested after 1500 hours, pull it and send it to a shop to be tested. It will narrow down your possibilities and it is not wasted money as part of good engine maintenance. Good luck and safe sailing.

Ard Righ · 14-06-2017, 05:07

Sorry with a delayed opinion I have been away for a time. My old engine (a BMC) gave exactly the same symptoms, I changed the air filter and it behaved impeccably once again.