Volvo Penta 4.3 GL ~2000 model year. no fuel - where are the diodes and what size are they

[plainman98]

So I can't start the boat. No fuel going to carb. Tested pump with direct wire. It pumps. Tested relay with direct wire. It switches. Tested relay coil voltage with meter and when key turns on, it jumps to 2V, not 12 V. Bad Diode? Any idea what the diode looks like and where to find it? Diagram shows the orange wire feeds from a diode connected to the starter relay likely key activated. It appears that once started, the alternator green wire feeds power to the pump. It makes sense that the diode keeps the starter from activating while the alternator feeds power to the fuel pump relay, so I don't want to just remove it. I've been searching for more information on where it is located and what it looks like. Any information would be super helpful. Thanks!

 

[djrevkev]

I actually just had similar problem. On mine with low pressure pump. I get battery voltage at yellow and red wire to pump when cranking but no fuel to carb. Pump would run with 12 volts supplied straight to it. Problem was it wasn't pulling from the tank line. I replaced fuel pump and it works perfectly. It may be something internal to the pump like my problem was.

 

[alldodge]

Tested relay coil voltage with meter and when key turns on, it jumps to 2V, not 12 V. Bad Diode?

It should go to 12V (on green wire), so either bad diode, alternator output not working, or bad wire connection
The diode is inline with the Green wire

 

[plainman98]

I took off the alternator and took it to 2 different auto parts stores to get it tested and both said they did not have the correct setup to test it. After finding the wiring diagram similar to the one @djrevkev shared, I believe the problem was with the yellow/red wire from the key, not the alternator. the green wire only supplies voltage from the alternator when the engine is running. When the engine is not running, the key switch supplies the 12V on the yellow/red -> orange wire and the diode in the wire keeps the alternator from running the starter once it gets going and the green wire is supplying voltage. I put the alternator back on and tried to find the diode, but did not. I was prepared to splice in a new wire with a diode, but on a whim decided to try and start the engine just one more time and it started, so it may have been a bad connection at one of the relays, or at the alternator, but it works now and no parts were replaced. This type of "fix" is super frustrating because I don't trust it will continue to run, yet it was a cheap fix ($0) with just some time. I now have a better appreciation for the simplicity of a carburated engine electrical system. Thanks all for your suggestions. It ran about 5 hours since and has had no issues starting. The moral of the story might be "check your connections before replacing parts."

 

[alldodge]

Lots of corrosion issues with boats. Could get a new relay plug and relay (same as marine) from the auto parts place. Cut the old out and replace

Or could replace with Merc style using a oil pressure switch

Have found some of the VP don't have the diode on the green wire. Only if the yel/red diode shorts will there be a problem with back feed