2006 4.3 GL (carbureted) fuel pump not working/ possible Back feeding issues.

[schneids15]

Hey all, My First post here on IBoats. Thanks for all the info everyone has provided me over the years and have saved me from posting stuff by reading others problems and resolving them for myself. That being said i have read many posts and cant quite find an issue like mine and hoping to find some insight.

I have an issue i am working on and would like some assistance. I have a 2006 4.3 GL that will not start. Brought it up to the garage and determined that there was no fuel getting to the carb. I pulled off the fuel pump wiring and put my Multimeter pins into the contacts. Cranked boat and no power to the contacts. I proceeded to test the Relay checking OK. I then checked the fuel pump fuse and the 7.5 Amp fuse is OK. After this i ran a positive and negative from the battery to a connector i made and put it directly to the fuel pump, Fuel pump runs OK. I ran the pump Manually for 15 seconds or so and filled up the dry Carb Bowl. I started the boat to see if it would run and it started up and ran. Once the boat had started the starter stayed engaged (12+ volts going to it) not bendix sticking. I proceeded to shut the boat off when i heard the starter staying engaged and the ignition would not work, next step pull the kill switch, It neither worked. Ran to the back and pulled the coil wire to shut off the engine. With this issue determined i started searching I boats forums and found lots of alternator related issues and diode issues. What i have done is pulled the purple off of the terminal on the alternator and started the boat. the boat will still not shut off and starter stays engaged. My volvo book i have goes to 2002 but i have been hoping the wiring diagrams for the GL i have been looking at would be the same in 2006 as 2002. Anyways has anyone had this same issue? After looking at the diagrams i see the fuel pump is fed from the YW/RD Start circuit wire on cranking and then the alternator feeds it after running. That is why i assume back feeding through the alternator keeping the start circuit energized keeping the starter on. still cant figure out why my motor stays running as the purple wire disconnected from the alternator should prevent the back feed to the energization of the coil and ruins my theory. However If i manually run the pump to fill the carb bowl then pull my fuel pump relay and start the boat it will run fine and the key shuts off the motor and the kill switch functions properly and the motor runs fine until the carb is dry that is. Any ways i have some time this morning to run some tests and i am going to do some diode tests and check around for more issues. I tried to be as detailed as possible to help with the diagnosis. Thanks guys. Josh

 

[Bondo]

Ayuh,.... Welcome Aboard,..... After readin' yer story, I'd take a closer look at the fuel pump relay, 'n the ignition switch itself,......

 

[schneids15]

Hey Bondo thanks for the reply. I finally figured it out. A couple issues. first of all the connection at the fuel pump was intermittent so i will solve that with a new connector. Second of all the diode between the fuel pump relay and starter relay is bad and is allowing power to flow both ways. Which in turn solves my issues. Here is what it resolved to be:

As the boat starts and the green terminal starts producing 12V on the alternator it feeds the fuel pump as per normal but with that diode gone it sends power back fed through the YW/R wire to the starter which in turn livens the starter and keeps it operating. AS for not being able to shut it off since the start circuit has power going to there it also sends power to the purple wire on the starter solenoid sending a full 12V to the coil as if you were cranking the boat over to start it. Since there is power going to the purple circuit it deems the ignition switch and kill switch useless for shutting off the motor. This has been by far a very simple issue to fix but a very complicated one to troubleshoot. Haven't had to study wiring diagrams like that in a long time. Hope this post helps anyone else with this same problem. Now i just have to search for what diode i need as the Volvo dealer will only sell me a whole new harness for 800 dollars. Josh

 

[bruceb58]

I know you have it figured out but this is what it should look like.

The diode only needs to be rated to supply current to the field side of the relay which is way less than an amp. 5A diode will be fine. A bigger diode is just more robust physically.

 

[Bt Doctur]

why not just convert it to the mercruiser type , it`s stupid to use a alt feed to run a fuel pump. lose the alt= lose the fuel pump?????????????????
just add the oil pressure switch to the green wire going to #85 and grab 12v from any source. you can T off the alarm switch just above the oil filter.

 

[bruceb58]

It's already wired up. Why change it?