fuel pump on 4.3l isnt getting correct voltage

[swtch7]

Hey, I was wondering if I could get some help. Last season my oil pressure sending unit went bad, so I jumped the wires for trouble shooting. This provided enough voltage to power the fuel pump and every worked fine. I started working on it this winter with a new oil pressure sending unit, but havent installed it yet. Im not getting enough voltage at the fuel pump.

Fully charged battery reading 12.4 volts
with the ignition switch on I get 9.5 volts at the fuel pump
when turning engine over its still 9.5 volts at the fuel pump.

if I check voltage at the sending unit its 10.4volts.

i have jumped the fuel pump and it works, any ideas on why im loosing voltage?

thanks guys.

 

[Fun Times]

Re: fuel pump on 4.3l isnt getting correct voltage

Is this a volvo or a mercruiser engine?

 

[Don S]

Re: fuel pump on 4.3l isnt getting correct voltage

You shouldn't see any voltage at all with the key on and the engine off (not running). At cranking, 9.5 is about normal. But you should see battery voltage when the engine is running. Volvo uses a diode through the alternator, if the alternator isn't charging, you could keep the 9.5 Volts, with a Mercruiser, you could have a corroded or loose terminal at the oil pressure switch for the pump.

 

[swtch7]

Re: fuel pump on 4.3l isnt getting correct voltage

Sorry, I forgot to mention that it was a mercruiser. 9.5 doesnt seem to be enough to kick off the fuel pump though. Im able to jump it to a battery and verify the pump works, so it seems asthough im loosing voltage somewhere. I just dont know where.

 

[zbnutcase]

Re: fuel pump on 4.3l isnt getting correct voltage

I have seen problems with the connector itself where pump plugs into harness...

 

[swtch7]

Re: fuel pump on 4.3l isnt getting correct voltage

ok so new update. I cut the connections and re did the wiring at the oil pressure sending unit.... still 9.5 volts at the fuel pump with it not kicking in. So.... I decided to hook it up again to my battery charger, still nothing. So i think the fuel pump is bad. HOWEVER, I just got a new fuel pump in the mail. Havent hooked it up to the fuel line, but I hooked it up to the wiring and it wasnt doing anything either. How do I tell if a fuel pump is bad or not?

 

[Don S]

Re: fuel pump on 4.3l isnt getting correct voltage

i have jumped the fuel pump and it works, any ideas on why im loosing voltage?

If the pump ran when you jumped it, why did you replace the pump. you have problems with the wiring getting to the pump. Either power or ground.

 

[swtch7]

Re: fuel pump on 4.3l isnt getting correct voltage

If the pump ran when you jumped it, why did you replace the pump. you have problems with the wiring getting to the pump. Either power or ground.

Yeah sorry for the confusion, at the end of last season I was starting to have problems and jumped it for testing purposes. This winter I tried jumping it and it didnt work. so I could have a couple of problems... The new fuel pump doesnt make anynoise when connected to the exisitng wiring.

 

[Don S]

Re: fuel pump on 4.3l isnt getting correct voltage

The new fuel pump doesnt make anynoise when connected to the exisitng wiring.

No doubt. Probably finished corroding, so your wiring going to the pump is now totally toast. Use a meter and test some things.

 

[swtch7]

Re: fuel pump on 4.3l isnt getting correct voltage

No doubt. Probably finished corroding, so your wiring going to the pump is now totally toast. Use a meter and test some things.

Hey Don thanks so much for you input, its very appreciated.

One last question for you.. I took my new fuel pump and hooked it up to an extra battery I had, all I hear is a click. no humming or anything. Could this new fuel pump be bad to? the battery is charged and at 12 volts