Help, my diesel engine won’t start!

I’m sure most boaters have experienced the sinking feeling of turning the key on the boat engine only for it not to kick into life. There are lots of great books on trouble shooting engines and people naturally leap into those like these 2 which I own.

Marine Diesel Engines: Care and Maintenance by Peter Caplen

Don Casey’s Complete Illustrated Sailboat Maintenance Manual

Well I managed to come up with a situation that I had not anticipated and had some interesting side effects.

I’m sure most of you remember to check the engine kill switch on the petrol (gas) powered outboard or inboard as a first step. Just for completeness, a gas engine needs an ignition system to operate that generates electrical sparks that ignite the fuel. Outboard engines and Jetskis and many larger boats have a ‘key’ with a quick disconnect that you attach to yourself. If you fall away from the controls then you pull out the connector and the ignition is shorted, stopping the engine. And to shut off the engine you can press on a button that does the same. How many off us have turned over the engine multiple times only to find the ‘kill’ cord has been pulled accidentally?

A diesel engine does not have a separate ignition system, instead relying on the compression of the fuel itself to ignite. Diesel engines have a higher compression ratio that ignites the fuel. A typical sailboat has a toggle that you pull to stop it, that happens to be connected to a long wire that physically decompresses the engine, stopping the self ignition of the fuel.

I happened to be helping a friend who had been having a lot of trouble starting his boat… and coincidentally also had been having problems with the batteries discharging. I have much less experience on diesels but I’d asked the ‘kill’ switch question, and he had pointed at a button with the function on the dash that appeared to be operating correctly. So once we have changed the batteries for charged ones we tried to start the engine… it turned over well but would not kick at all… then we entered into the classic set of troubleshooting. First checking the fuel/water separator, fuel filter etc. All needed work but even after that nothing. Fuel flow before and after pump was checked. We also stripped the glow plugs to show that they were working… still nothing and by now the battery is getting faint. At this point we have a pretty good knowledge of the fuel system and there is one part that we have not checked …  some inspiration grips us and I check the wire to it and it has no voltage on it when the key is turned… I disconnect it and touch it to battery positive and the unit clicks…. We turn the start key and voila… the engine starts. It turns out that this is the fuel cut off solenoid and it has been de-energised constantly. Some tracing later we find an owner (previous)  installed ‘security’ immobiliser switch under the dash that is on, cutting off the the solenoid by shorting the key switch and thus preventing fuel flow into the engine. This happened to be wired in such a way as to create constant current draw on the battery which explains why the batteries were constantly drained after a week or 2 away.

So our lesson here is that the simplest explanation is so often the right one. Although we had fun troubleshooting it and I learnt more about diesel engines in the process.