Yanmar 45 hp marine engine, hot or cold, has to be cranked over around  4 to 6 times before it will start and run, Using pre heat, from cold.

Also after priming. My own experience in the past, on car engines this would indicate low compression. The engine hot does not breath thru the rocker cover or dip stick tube.

Any advice would be gratefully accepted.

Regards

Thank you.

Tom  

Like all engines many checks should be made during a service interval.

As you said check compression is within tolerance.

When cranking if it is slower than it should be indicates Battery or wiring connection faults. 

Is the fuel pump pressure correct. 

Fuel filter checks. 

Fuel injector checks. 

 

Yanmar - the ones I have worked on - have a mechanical fuel pump. The engine needs to be turning over for the pump to pressurize the fuel rail/injector pipes.

As above - what is the pressure exiting the pump ?

Modern FI systems have an electric pump to build pressure - be surprised if Yanmar use these.

I had a Volvo diesel which did a similar thing. It turned out to be a faulty seal in the injection pump which was allowing fuel pressure to drop when the engine was switched off.

Hi, thank you for the information, most helpful, interesting to know about the mechanical fuel pump, explains a lot.

Regards

Tom

Some mechanical fuel pumps have a hand lever or plunger built in. This allows you to fill the fuel filter after changing and prime the pump.

If your model has one, might be worth a try to see if pumping it up until you build pressure - the effort will increase considerably when the pressure builds. If it fires right up - you have found your problem.

YouTube has a bunch of videos on this - check them out.

Yanmar mechanical fuel pump

 

 

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Tom, I think you have become used to direct injection diesels in motor vehicles that start immediately on turning the key. I doubt very much this small marine engine is DI, therefore I would suggest that 4 -  6 revolutions before firing is normal. Some engines are just like that.

The only other suggestion I have is to find a marine forum, ask if anyone has the same engine.