Volvo 4.3 GL Diode, Starting question

Dj2660

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Here?s my story, out boating in the bay for about an hour in fairly rough water. Anchor by a small island, few hours later, go to start and starboard motor fires then dies, repeat, fires then dies, repeat the process same result. Start port motor and go home.

On the lift, check spark, got it, check fuel in carb, got it. Change fuel filter, check fuel from filter, no water. Start motor, runs about two minutes, stalls. Try to restart, fires then dies, fires then dies. Come in, check forum FAQ, discover that starter provides power to fuel pump then changes to alternator. Remove alternator, have tested, guy says no output, thinking I?m on right track, replace alternator.

Start motor, runs about two minutes then stalls, during which time I glance at voltage gauge looks like 10.5 to 11 volts, but this is right before motor stalls so I am not sure if that was accurate. Try to restart, fires then dies, same story. I see in FAQ that a diode may be bad, problem is, I have no idea where this diode is, excuse my ignorance, or what it looks like. I should add, I replaced relay from port motor, no difference. Also port motor runs fine so I am ruling out fuel tank vent. Any other ideas? Where the heck is this diode and what does it look like? Sorry I am at work and do not have serial number.1998/99 Volvo 4.3GL. Thanks in advance.
 

bruceb58

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Re: Volvo 4.3 GL Diode, Starting question

There are going to be two diodes. The alternator feeds one from its L2 terminal and the other diode is fed from the wire that comes from your ignition switch. The diodes are there to keep one side from back feeding into the other. If you didn't have the diode on the starter side, the alternator output would cause the starter to turn. Not exactly sure what would happen vice-versa.

If you don't have 12V at the output of the L2 terminal once the engine is running, the fuel pump won't stay running. What I would do right now is to bypass the relay and get the fuel pump running, start the boat and check the voltage at the alternator to see what it is doing.
 

Don S

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Re: Volvo 4.3 GL Diode, Starting question

discover that starter provides power to fuel pump then changes to alternator. Remove alternator, have tested, guy says no output,

No output from alternator, no power to the L2 termanil, which means no power to the fuel pump.
 

Dj2660

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Re: Volvo 4.3 GL Diode, Starting question

The alternator has been replaced, I haven't tested power at L2 but I 'm hoping that a new alternator would be powering it. My problem is the wire that leaves L2 disappears into wiring harness, the green wire that connects to relay, emerges from wiring harness and enters relay. My question is where is the diode?
 

Don S

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Re: Volvo 4.3 GL Diode, Starting question

My question is where is the diode?

Somewhere in the harness across the front of the engine. Under all that tape.
 

Dj2660

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Re: Volvo 4.3 GL Diode, Starting question

Under all that tape

Crap, I was afraid you were going to say that.

Down to the boat with a little more test gear.

Thanks Don.
 

bruceb58

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Re: Volvo 4.3 GL Diode, Starting question

I really really doubt that your diode went bad but I guess there is a small chance. The current going through the diode ony powers the relat so unless a huge short occured that put a lot of current through the diode, you are probably fine.

One thing you could do is to take the wire off the L2 terminal and appy 12V to the wire and see if the fuel pump goes on. That would test a lot of things with one test.
 

Dj2660

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Re: Volvo 4.3 GL Diode, Starting question

I'll be headed down to the boat in the morning with a multi-meter and test light. I will also try your idea as well. Thanks
 
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