Troubleshooting engine electrical problem

[ddoles]

I'm faced with an engine that suddenly decided not to start. All was well from one day to the next when I went to start the engine and nothing happened. Turning the key would normally start the fuel pump and with a little glow plug and a push of the start button the engine comes to life. I checked the starter battery voltage and got the expected 12.8 V. Similarly, I get 12.8 V on the battery side of the key switch. Turning the key switch to the on position, I got 0 V on the load side of the switch. I assumed then the key switch was the culprit and was a quick and easy fix. With a new key switch in place, I got the same result.

Delving deeper into the panel wiring, I see that there are two wires connected to the load side of the key switch. One goes to the glow plug and ignition button, the second wire powers all the panel gauges, oil light and fuel pump. Through some experimentation I discovered that with only the first wire connected to the key switch, with the key on, the circuit was powered, with 12.8 V at the glow plug and ignition button (but even then, the ignition button would not turn the engine over). However, with the second wire connected and the key switch on, I get 0V everywhere on the load side of the key switch, and of course no fuel pump running or engine starting.

I tried disconnecting each gauge to see if I could find perhaps a bad actor in the circuit, but so far nothing has worked. With my rudimentary electrical knowledge and multimeter in hand I will do some more troubleshooting, but I want to see if anyone has any guidance to offer. Any thoughts, comments, suggestions on troubleshooting would be greatly appreciated.

Some other points of note, the key switch, start button, fuel pump and start battery have all been replaced within the last 3-4 years. The starter was rebuilt 2 years ago. So I think these components should be in good shape. Everything else is original equipment, as far as I know, including the wire harness.

Thanks

Dave

 

[Frank Langer]

Hi Dave,
This one is puzzling and may require the real experts to chime in, and I'm sure some will. But when I have a sudden failure like this, the first thing I check is if all the ground wires are connected properly. Just a thought for what you might check with your multimeter while waiting for the experts.
I have found that the engine vibration sometimes loosens the connection, or in one case cracked the copper loop which was hard to find as it looked solid till I tried to wiggle it and noticed the break.
Frank

 

[G Kiba]

My ignition switch (yellow and red strip) is wired to a solenoid which actuates the power to the starter solenoid and the glow plugs. It is fused. So in addition to checking grounds, you may want to check fuses - if they are present. Mine are in-line ATG style fuses that a PO had added.

 

[Jerry VB]

I agree with what Frank and G Kiba wrote on checking grounds and fuses.

Some additional diagnostics and observations:

Your symptom (12v at the glow plug/ignition button when they are off, 0v when they are on) indicates you have a bad connection (loose or corroded), not a short. The 12v source can supply 60A+ which would turn your gauge into smoke if there was a short in a gauge. If you have a bad connection, it behaves like a resistor which allows 12v to be read when there is no load, but, as soon as there is a load, the voltage drop across the bad connection goes to 12v and your measured voltage goes to 0v because all the voltage drop is at the bad connection.

Since, when you push the ignition/glow button, the voltage you read remains 12v but the engine doesn't crank, that implies the ground from the engine to the battery is bad.

Since, when you connect the panel power (loose lead), the measured voltage goes to 0v, that implies either the panel ground is bad (the switch actually stayed at 12v but the ground got pulled up to 12v as well, resulting in a measured 0v) or the power going to the panel is bad.

Connect a temporary wire from a known good ground (ideally the battery post) to the "-" side of your meter and then check for voltage against the known good ground. If the voltage still goes to 0v at the ignition/glow button, the bad connection is between the battery and the ignition switch. If it stays at 12v, the bad connection is on the ground side. Note that you may very well have multiple faults - I'm suspicious of the ground wire that goes to the panel as well as either the power going to the panel and/or the ground going to the engine.

 

[ddoles]

Thanks everyone for the insight and suggestions. I expect to get back to the boat next week and jump into the problem. Hopefully, I'll have some progress to report.

 

[ddoles]

I have solved the problem. Upon more thorough checking of wires, connections, etc. I discovered the problem was a bad connection. Essentially what Jerry VB suspected. Specifically, it was a loose connection at the crimp to the in-line fuse holder in the wire leading into the key switch. I think I was seeing 12.8 V reading at the key switch because there was some contact, but with the bad connection the current was insufficient to do anything useful. I replaced the fuse, fuse holder, related wires and ring terminals and everything works perfectly.

What this drives home is that I'm depending on 33 year old wiring, fuses and connections to start the engine. Mostly it works, but at any time the next connection can fail. A complete rewire is something I should put on the list, maybe as my next winter project.

 

[G Kiba]

I just finished rewiring my engine control panel, harness, and connections to the engine this month. I did it in stages so I could keep sailing. It was a lot easier than I thought. The mass of wires was at first, intimidating.

I started with finding a wire diagram online. Then I created a diagram of what was on my boat. This took a good amount of time to do but it was worth it. I rewired the panel first by adding a terminal strip. The strip allowed me to consolidate power and grounds to the panel while maintaining a connection to the harness so I could test my work and keep on sailing. Once the panel was finished, I created a new wire harness (with the right colored marine wire and plastic split conduit to hold it all together) and connected it to the engine and terminal strip. Done.

Additionally, I consolidated fuses with a BlueSea fuse box, I labeled each wire, and I routed the harness away from engine heat and dirt.

I found both these vendors to be really good. I really like the terminal connectors from Pacer. They have connectors with heat shrink with adhesive. I found the quality very good and I am in the process of rewiring the AC with their flexible 10-3 made here in the USA. Best marine wire lets you buy 25' lengths in different colors and gauges.

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