Ignition Problem on Yanmar

[Gripfast]

Will this relay work? 5 PACK 40/30 AMP 12 V DC Waterproof Relay and Harness - Heavy Duty 12 AWG Tinned Copper Wires, 5-PIN SPDT Bosch Style Automotive Relay https://www.amazon.com/dp/B074FSZWVT..._mnV.CbSABA58E

[transmitterdan]

Yes, that relay will work.

[Tusitala]

Where should it installed? Should it be close to the starter, the ignition switch or doesn't matter?

[JimsCAL]

The relay fix for Yanmars is a well doucmented issue. Seems if the wire run from engine to panel is too long and due to the high current being carried, voltage drop can prevent the starter solenoid from actuating. Commonly OK on a new installation when everything is clean and shiny, but becomes a problem as things get older. Relay should be installed at the engine so the high currents are carried in the shortest wire run possible. Previous owner of my boat with 3GM30F had done it and I have had no issues in 10 years of ownership.

[Tusitala]

Thank you Jim.


Pat

[transmitterdan]

Originally Posted by Tusitala

Where should it installed? Should it be close to the starter, the ignition switch or doesn't matter?

It should be close to the starter.

[JSurr]

Well I am able to duplicate the issue. I jumped straight across the solenoid from M terminal to B terminal, bypassing all the switches, wiring and connections, and instead of the starter spinning, the exact same thing happens. The DC buses shutdown and the starter doesn't spin. Leading me to a problem with the starter.
Now to the arduous task of pulling the starter. It doesn't look like it's going to come out easy. No room to work and no room to get it out of the engine compartment

[transmitterdan]

What does it mean “DC busses shut down”? Tell us what happens to the battery voltage measured right at the battery terminals when you try to jump start the engine.

This may not be a starter issue at all.

[donradcliffe]

Originally Posted by JSurr

Well I am able to duplicate the issue. I jumped straight across the solenoid from M terminal to B terminal, bypassing all the switches, wiring and connections, and instead of the starter spinning, the exact same thing happens. The DC buses shutdown and the starter doesn't spin. Leading me to a problem with the starter.
Now to the arduous task of pulling the starter. It doesn't look like it's going to come out easy. No room to work and no room to get it out of the engine compartment

Your diagnosis fits a weak connection from ground system to the negative terminal of the battery. You can test this by running a jumper cable from the battery terminal to the starter case, then repeating the test you described.

[donradcliffe]

The tool that helps diagnose these kinds of problems is the clamp on DC ammeter.

Clamp the ammeter around the wire coming from the negative battery terminal and push the start switch. If you have a good negative connection you should see 100's of amps as the DC buses shut down.

[jimbunyard]

Originally Posted by JSurr

Well I am able to duplicate the issue. I jumped straight across the solenoid from M terminal to B terminal, bypassing all the switches, wiring and connections, and instead of the starter spinning, the exact same thing happens. The DC buses shutdown and the starter doesn't spin. Leading me to a problem with the starter.
Now to the arduous task of pulling the starter. It doesn't look like it's going to come out easy. No room to work and no room to get it out of the engine compartment

I'm not exactly sure why you think this leads you to a problem with the starter.

Did you have a problem with it before, clicking, a gradual reduction in start speed, something like that?

If not, it sounds more to me like you have a loose/poor connection at one or more of the main power sources, either ground or hot. Since it shuts the whole thing down, I'd guess it was between the batteries and the main buses, but I'd check all connections for tightness and corrosion, starting at the batteries and working toward the main switches, buses and starter.

Removing them all, wire brushing and coating with some sort of anticorrosion product may seem a bit ambitious, but it would be a good preventative measure to take, and would also enable you to check the main cables individually for hidden internal corrosion, a relatively common occurrence.

A relatively stiff section of a wire or cable, as compared to the rest of the same wire or cable, is a good indication of internal corrosion. Poor crimping is also a source of connection gremlins....and can be hard to recognize, especially when hidden by heat shrink.

[mikedefieslife]

You can take some automotive jumper leads and run them from the batteries direct to the starter. Be prepared for sparks on connection. That will tell you if the starter is bad. You can do this with starter on a bench (held down) but I did it on mine with it still attached.

In fact, for 3 months by-passing the (dead) solenoid was the only way to start mine. I used a big battery switch and left the wires permanently connected, until I could get a new solenoid.

Another thing, as others have said, get a clamp meter (brilliant tool to have on the boat), make sure it's a DC one though. Startup current for me is around 200 amps or so.

[JSurr]

To continue from easiest to hardest with diagnosing this mystery, and since the starter on this engine is quite difficult to get to, I will measure the amps as suggested to diagnose further. It will give me an excuse to go out and buy one.

[transmitterdan]

JSurr,

Did you ever measure the battery voltage directly at the battery terminals when trying to start? That is by far the easiest and most useful measurement you can make.

If the battery voltage drops to <10V when attempting to start you have bad batteries. But only measure right at both battery terminals.

[Tusitala]

I don't know how Gripfast & JSurr made out, but I bought and installed the relay Gripfast linked. Easy job, problem solved. Thanks guys.

Pat