Diesel hard to start

[Ross]

Resetting the rack sounds like voodoo or some other doo but try what I said. If my engine doesn't start in the first two turns I release the button and pull the stop handle and try again and always have success. Also if I just persist with cranking and it does finally start it take quite a while to come up to speed and to run smoothly.

 

[larryw]

There's a lot of advice here; most diesel, or any engine, problems stem from too little use. Add a bit of Marvel Mystery Oil to your fuel, and every time you run the engine, be sure to motor for a while, WOT for ten minutes after it's warm. Does a world of good.

 

[filthy liberal scum]

Maine sail;
I know that manufactures and mechanics say not to use any starting fluid. however some diesels are a bitch to start in cold weather. engines that have been exposed to low temps such as close to freezing and do not have glow plugs to preheat the cly can be difficult. I'm not saying to use it all the time. the amount of starter fluid has a definite factor as to whether there will be any damage done. you give an engine a 3 or 4 second shot and i agree you could do some damage. a 1 second shot is enough. in cold weather this is a lot easier on the engine than cranking for a minute or two to get it going. the qm series engine was originally designed for small tractor use and it had a place in the intake manifold for a heater to be installed. however they never put any of these in the engines installed for marine use. i suppose you could do what some people do and run a hair dryer into the intake to help but i find that to be a pia. WD40 is used sometimes but it has petroleum distillates in it that's close to gasoline.
my father-in law used to work for nasa and wd 40 was developed for the space program. wd40 actually was "Water dispersant formula#40"

 

[filthy liberal scum]

one key thing to a quick starting diesel is to have good compression. lower compression due to engine wear will be a key factor. be that rings or valves. cetane is rarely a factor, as is old fuel. my boat was on the hard for 2 years. fully charged the batteries and it started right up on the old fuel that had been in the tank for close to 3 years.

 

[RichH]

In one of your posts you referred that the injection pump was replaced. Did you ever go back and re-tighten all the high & low pressure fuel connections ???????? That the injector pump was replaced and that you now have starting problems would suggest that maybe the injector pump was NOT the problem, etc. It then follows as good possibility that there is a cracked (or loose) fuel line / connector in your system .... why was the injector pump replaced??? The cheapy compression fittings used on boat fuel systems are notorious 'leakers', should be only tightened ONCE (before retightening, the tubing should be trimmed and the internal connection ferrules should be replaced - better to use double flared connections ... BTW, NEVER use PTFE tape or 'dope' on such fittings to make them 'seal'.
The cheap copper tubing used in the fuel supply line is 'reactive' with most diesel fuels - developed pin hole on the suction side?? The lift pumps on QMs are easy to break ... pin hole in the internal diaphragm which allows fuel to slowly drain/bypass into the crankcase during moderate to long term engine shut down?
If the engine is physically located higher than the 'highest' elevation of the rest of the fuel system ... and if one (or both) of the check valves in the lift pump is faulty, the fuel can flow/drain retrograde back into the tank when the engine is shut down ... leaving air in the fuel line section close to the injection pump - hard starting. Most Yanmars are NOT 'sensitive' to moderate amount of air in the fuel line, they will easily start with 'some' air in the system. If this is an air leakage problem you will probably find a LARGE amount of air in the delivery system.

A quick check to validate the integrity of the low pressure side of the fuel delivery system: If you have the expertise - install a vacuum gage into the fuel line, shut off the tank valve, install a tee with cock valve and apply vacuum, then shut cock valve. Watch the vacuum gage ... if the vacuum gage slowly over time returns to "0", you HAVE an air leak in the low pressure side of the fuel system: tubing, connectors, filter(s), lift pump diaphragm ... and that leak may be causing the fuel to drain back to the tank (or crankcase) during shut down. Next time when shutting down, close the tank valve and reopen when you later return and see if the engine starts 'easier'. If so, you HAVE an air leak in the delivery system; if so, trace the system to find out where the oil is 'going'.



For super cold temperature starting I do the following to start my QM:
• Throttle set at HALF.
• Decompression OPEN ... on most Yanmars, decompression is usually NOT hooked up nor connected to a 'stop button' (to stop a Yanmar you pull the 'idle kick' to stall the engine). The linkage that runs along the port side of the engine at the valvecover is the decompression assembly ... just move the linkage by hand.
•With the decompression OPEN, SPIN the engine with the starter, once engine is spinning (at max.) THEN close the decompression. The speed of the rotation will build the inertia of the rotating parts; suddenly closing the decompression lever with little load on the starter (least resistance to the starter) will usually cause sufficient compression to start.
Yanmar engines usually can last through 8-000-10000 total engine hours without 'noticeable' compression loss.

Most likely, there is a VERY SIMPLE reason, that you have 'hard starting'; just be patient and check out everything slowly and 'methodically'

hope this helps

 

[Hermit Scott]

When I first got my boat there were starting fluid cans in the engine compartment. The po said "you'll live on this stuff". Apparently it was used quite often. When I disassembled the engine there were no burnt rings or damage to the cylinder or vavles that I could tell. I used the same connecting rod so it wasn't bent. The top of the piston was pitted. I am not sure why, could have been starting fluid or something else.
The only problem with that engine I could tell were that the rings were seized. Starting fluid could have caused that, but the guy said it ran the last time they were messing with it so probably not.
Really if you have to use starting fluid AT ALL, you have other problems. I would never use starting fluid, however I didn't see any major apparent damage in the engine I have and the guy "lived on it" to start it.
The engine is a ysm12 and it starts in half a second on cranking every time. The first time I put it together I couldn't start it becasue I didn't properly bleed the fuel line.
I would start at the tank and work my way to the injector on top the head. You most likely have a fuel related problem.
Checking the compression would be a good thing to do, but it's not as easy as gas engine, I think you have to take the injector out and put a compression-tester fitting in there. When I took mine out, I had the head in a vice clamped to a 500 lb. welding table. I used a 4 foot long cheater pipe to turn the injector. I thought it was threaded, it actually just slides in and out. You could say it was seized.