fuel pump low voltage?

[wgj45]

1997 volvo penta 4.3 gsplkd fuel pump will not run when starting. The engine will start if gas is sprayed into the carb. I jumpered the fuel pump with 12.7V from the battery & it pumps ok. Checking voltage @ the connection for the pump while starting I only get 10.7V. Checking the relay connection, 30 to 86 is 12.7 V. 30 to 87 is 1.35V with the key on & 10.7V in start position. Would the voltage be too low to run the pump? Why might it be this low?

Also checking @ the ignition it is 12.7V in and only 10.7V out with key in start position.

 

[gm280]

:welcome: wgj45 to iboats. Glad you joined us...

You could have a couple issues. When you jumped straight from the battery to the fuel pump it ran. And that is because it could be needing a lot more current and jumping supplied that current. The fact that the voltage is low when you read across the relay could be that the relay has burnt contacts OR the lock in voltage is not high enough to pull the contacts closed properly. So start cleaning the contacts from the battery forward to see if you have some corroded connections or the relay itself is bad. And if all that checks out good, then maybe the pump itself is needing changed. JMHO

 

[bruceb58]

When you are cranking, you should have 12V from pin 85 to 86. The diagram says ignition switch. It's actually the start side of the ignition switch.

With just the ignition on, there is nothing happening so don't worry about it. Pump relay only gets energized by cranking and by voltage off the L2 terminal of the alternator when engine is running.

With the relay out, jumper the pins 87 to 30 and pump should start running. Measure voltage while the pump is running. Should be full battery voltage.

 

[wgj45]

If I understand correctly the pump must be receiving full voltage to run. In my case I am only getting 10.7 V which is a drop of 2 V. Are you saying the pump will not run with a 2 V drop? I have cleaned all the connections I can find and still have a 2 V drop at all point I check, including @ the starter. With the relay out 30 to 87 reads 12.7 V with key off, 12.7V with key on, & only 10.7 V with key start. I'll try a jumper as suggested..

 

[bruceb58]

You do not measure from 30 to 87. You jumper from 30 to 87.

Do this...remove relay and jumper from 30 to 87 and see if the pump runs. At the same time measure from the jumper to ground(pin 86). Should be battery voltage. If that is low, measure from the jumper down to the engine block.

If that works, buy a new relay.

 

[StarTed]

If the engine is cranking the voltage will drop some. 10.7 is not that unusual for a heavily loaded battery while cranking an engine.

Check the voltage on the battery posts while cranking and again on the lugs. You shouldn't see any difference or the connections aren't clean enough.

There shouldn't be any voltage across the relay while cranking. A voltage reading there indicates poor connections in the relay.

 

[bruceb58]

If the engine is cranking the voltage will drop some. 10.7 is not that unusual for a heavily loaded battery while cranking an engine.

+++++1

 

[wgj45]

When I remove the relay and jumper from 30 to 87, the pump does run and pump gas into and from the line going into carburetor, which I have running into a bypass jug. The voltage on that jumper to ground (pin 86) is 12.1 V, while the pump is running.

Checking the battery while cranking the 12.7 voltage drops to 11.0 V. The posts and lugs both have the same V drop. Good connection there.

When I check voltage at the relay connection they measure the following:

Key off /Key run/ Key start (cranking)
30-86 /12.7 V /12.7V/ 10.7V
30-87 /12.7V /12.7V /10.7V
30-85 /0V /0V /0V

 

[bruceb58]

Measure the voltage from 85 to 86 while cranking without the jumper. Should be 11.0V minus diode drop.

Add the jumper, start the engine and measure 85 to 86 again. Should be around 13V.

 

[wgj45]

OK Measured the voltage from 85 to 86 with key off 0V, with key on 1.3V, while cranking 10.2V. Added jumper and started the engine. measured 14.2V from 85 to 86.
It only took 3 short attempts to start the engine.

 

[bruceb58]

With those voltages, all your wiring up to the relay connector is perfect.

Replace the relay and you should be fine.

 

[wgj45]

What is the procedure to check the relay?

 

[GA_Boater]

Doing the last step and getting the motor started. you just did. Get a new relay.

 

[wgj45]

Decided to try checking the relay. It has continuity between 30 and 87A but none between 30 and 87. Put 12 volts to 86 and 86 and there was a click sound. At this point there is no continuity between 30 and 87A but now has continuity between 30 and 87. I assume this tells me the relay is good?

I put the relay into the relay contacts and again try to start the boat. The boat starts and run normal.

I'm thinking: perhaps the fact that the boat has sat for nearly a year that the pump just would not pump at 10.7 volts. After jumping the pump from the relay contacts 30 to 87 with 12.7 volts and the pump ran for a bit it was enough to allow the pump to run at lower voltage. However I won't get far from the dock for a while.

Maybe I need to carry a spare pump and relay. I certainly will carry the jumper I made for 30 to 87.

Thanks for all the good advice and patience. So far I'm not out any money, just many days working on this. I hope for better days for all of us!

A boat is a vessel that makes a hole in the water and you through money into it.

 

[gm280]

Could be the fact that you removed the relay and installed it back may have cleaned the socket terminals enough to allow it to work again. :noidea: