1993 Volvo penta 431 no power from alternator to fuel pump

[mrwalters]

Hello, this is my first post here. I have a 1993 Tiara 270 with twin Volvo Penta 431's. The other day I stayed aboard overnight and when I tried starting the starboard engine it would only run for about 30 seconds. After researching I figured out that the fuel pump gets power during cranking from the ignition switch, but then gets its power from the alternator. Seems like a simple enough fix. however there is another thing that is also troubling me, related to this. When I turn the ignition switch for the port engine I have a Christmas tree of 4 LEDs on the dash light up along with gauges that bounce to position (battery power, etc) and when I turn the ignition switch to "ON" on the starboard engine (the engine that is not charging from the alternator) I do not get any LED's light up. The gauges do bounce (voltage, etc)
What I am wondering is, I realize that the alternator only outputs power when it is spinning, is there another problem occurring that would cause my LED's not to light up regarding the starboard engine. Also, I have no buzzer for either engine, and I think I used to have that as well. I'd hate to replace the alternator to find there is a fuse or something else inline that could be a problem. I can't readily locate any fuses, are there certain places for these, or the inline diodes? I realize that many of you are highly technical, and I welcome any answer, you can be as technical as you like. Thank you in advance for any guidance. Joe

 

[alldodge]

What is a motor serial number?
Did a search on the 431 and it comes up as a V6 and a V8

 

[mrwalters]

I do not have a SN handy as of right now, but I can get it when I head back to the marina It is a 431B (I believe) , which is a v6 block, Carb style, red engine.

 

[alldodge]

OK, Being a carb I'm wondering if its similar to the GL
I have diagrams for the GL and they use 2 diodes (Start and Run). This diodes should be found at or near the fuel pump relay

Having the 2 diodes would not explain the "no light up" because this would come from the ignition key. As example here is the GL-C/D

 

[mrwalters]

Thank you for the wiring Diagram, it helps. From what I gather, I should apply battery voltage directly from b+ on the alternator over to the wire that excites the alternator and see if I can get the alternator to output power to the fuel pump. I wish I knew where the wires to the alternator route and land to. I guess I will have to do some poking around.

 

[alldodge]

The purple wire is what keeps the motor running. Check for 12V at the ALT to see if its powered up. Then check the Green wire which goes back to the FP relay.

Note there should be 12V on the purple wire when the key is turned ON, and doesn't matter if motor is running or not

 

[QBhoy]

What is a motor serial number?
Did a search on the 431 and it comes up as a V6 and a V8

Identical to the AQ205 4.3 V6 AD. Just with a fuel pump signalled off the oil pressure switch.

 

[QBhoy]

Hi.
I had the almost identical engine to this years ago. The aq205. The 431 came just after and only for a couple of years or so. On my dash, there were fuses for the ignition that are worth checking. Yours may be under the dash. Mine were in it. Glass fuse type.

 

[REVKEV91]

OK, Being a carb I'm wondering if its similar to the GL
I have diagrams for the GL and they use 2 diodes (Start and Run). This diodes should be found at or near the fuel pump relay

Having the 2 diodes would not explain the "no light up" because this would come from the ignition key. As example here is the GL-C/D

View attachment 355446

Hi mate I'm currently having trouble with my 4.3gld and need to replace the diode item 23 on the green wire. Do you have any details on what the diode is. Just trying to buy a replacement.

 

[alldodge]

Hi mate I'm currently having trouble with my 4.3gld and need to replace the diode item 23 on the green wire. Do you have any details on what the diode is. Just trying to buy a replacement.

I posted this on "your thread" also
If a diode is needed, buy a 1 or 2 amp diode online or local electronics parts house. Cost for VP part is $25 and a 2 amp diode is about 50 cents