1998 GS Volvo Penta Fuel pump relay...

[GregB20]

I am losing power to the fuel pump relay after engine starts. Is the relay energized by the alternator at this point. If so, can the alternator be reworked to remedy this issue. Thanks in advance...

 

[bruceb58]

If your engine is a carb model then the alternator drives the relay. Measure the voltage at the L2 terminal of your alternator. Green wire. If you have voltage there, then you either have a bad relay or the diode going to the relay from the alternator has failed. Diode failing is very unlikely.

 

[GregB20]

Thanks Bruce. We checked it yesterday while engine was running and the only power coming out of the alternator was the main wire. None of the others had power. I think I have found problem. Thanks.

 

[bruceb58]

Your excite line(purple) needs to have power. That is supplied by your ignition. Your alternator may be fine.

There should be a red jumper between the Sense and Excite connections.

 

[GregB20]

Ok. Took alternator off and went to have it checked. It checked ok. Put it back on, now the starter is staying engaged and the key wont kill ignition. Had to disconnect battery to kill engine. Now what???

 

[GregB20]

Could this be a bad ignition switch causing all of this???

 

[bruceb58]

If your engine stays running with the ignition off, that points to a bad alternator/regulator. Basically the alternator is staying excited with power removed from the excite pin.

You said starter stayed engaged. Is that really true?

Just so you know, the guys at an auto parts store are just checking that the alternator has an output. I wouldn't let one of those guys touch my alternator.

 

[bruceb58]

With your ignition off, measure voltage at excite pin..should be 0V.
Turn your ignition on. measure voltage at the excite pin..should be 12V.
Start engine and then try to turn off with ignition switch. measure voltage at excite pin..should be 0V again.


One more question...before all this happened, did you ever disconnect the battery while the engine was running? If you did, that could be why your alternator failed.

 

[GregB20]

Yes, starter is staying engaged. And the key wont kill the engine. I dont know how else to kill the engine without disconnecting the battery. I never touched the battery BEFORE the first time this ever happened. I had the alternator checked by a shop. And your right, all he tested was that they were putting out, because he wasnt sure of what they were supposed to be doing.

 

[GregB20]

ONe more thing, when we checked pin 87 on the fuel pump relay while engine was running(briefly because we jumped the fuel pump pins to get some gas in carb), we had no power. Now, if I understand correctly, the alt energizes that pin once engine cranks. Could the diode on the ignition switch be open allowing the starter to be sucking all the juice from the alt thus causing the starter to stay engaged and the ignition not killing engine???

 

[bruceb58]

Pin 87 is the one connected to the fuel pump. When the relay closes. it is connected to power from pin 30 across the relay contacts.

The diode from the ignition switch(starter side) does almost appear to be shorted across it which would cause your problem. Typically, diodes don't fail that way but it sure appears that's the case here.

You could test that theory by jumping pin 87 to 30 to run the pump and remove the green wire off of L2 at the alternator and see what happens when you turn the engine on and then off again.

Out of curiosity, how long have you owned this boat and has it ever worked correctly?

 

[GregB20]

Well, I bought the boat about 5 weeks ago. Ran fine till this past weekend, except for one other time that it went dead and took about 3-4 mins to crank. Then ran fine again. What would removing L2 tell us if the motor is running? Any idea where the diode on the starter side is located?

 

[bruceb58]

Removing L2 would let you know if the alternator was back feeding the starter.

Diode is buried in the harness.

 

[GregB20]

SO, your saying crank the motor and THEN remove L2 while its running?

 

[bruceb58]

Pull the relay out
Remove wire from L2
Jumper the socket pins 87 to 30. pump should turn on.
Start engine and see if starter is still engaged
Stop engine...hopefully.

Repeat with L2 connected. Should exhibit the behavior you saw before.

 

[GregB20]

Ok. here we go. undid L2, cranked engine, no starter hang and key klilled engine... plugged back in, cranked engine, no starter hang and key killed ignition,...:-(. tested L2 while engine was running, no output. Now what???

 

[bruceb58]

You need a new alternator since there was no output on L2.

 

[GregB20]

I think the one of the diodes went bad. I am getting all kind of backfeed. Thats whats causing the starter to stay engaged sometimes. I did once get power from L2. I think the backfeed is shooting all over the place and getting screwy. What diode goes in there?

 

[bruceb58]

Do this. With the engine off, fuel pump relay installed, and the L2 wire removed, use a jumper wire and connect the L2 wire to 12V. The only thing that should happen is the fuel pump turns on.

 

[GregB20]

Starter side diode is bad. Tested it and flowed both ways. Which is why the starter would stay engaged sometimes. I guess it was backfeeding into the alternator and sending voltage everywhere it shouldnt be. What diode goes in there???