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Fuel pump voltage

J

jrowell

NAXJA Forum User
Location
Bakersfield
Trying to Diagnose a loud fuel pump in another thread, thought I might get more response to this question in OEM Tech...

Got the volt meter out to find at the fuel pump harness i'm getting: Red wire- 9 volts. Orange/middle wire- 3 volts.

I'm guessing low voltage could be the cause of my loud fuel pump??? Any ideas as to WHY voltage is so low at the harness?
What sends power to the Fuel pump? What should the Voltage be on those 2 wires?
 
The 87 should have a ballast resistor so the running voltage will not be 12v. Your voltage is within reason. The other voltage is the fuel level signal.

Loud on the pump can be caused by the rubber "stopper" looking thing that is supposed to be on the end of the pump and fits into a bracket in the bottom of the tank. If it is gone, the pump will rattle against the tank with no cushion and will make a ton of noise.
 
old_man said:
The 87 should have a ballast resistor so the running voltage will not be 12v. Your voltage is within reason. The other voltage is the fuel level signal.

Loud on the pump can be caused by the rubber "stopper" looking thing that is supposed to be on the end of the pump and fits into a bracket in the bottom of the tank. If it is gone, the pump will rattle against the tank with no cushion and will make a ton of noise.
Click to expand...

Actually, 1987s came without the ballast resistor. Excessive fuel pump noise complaints from customers were addressed with a kit to install the ballast resistor and associated wiring. When done, it looks like factory. The resistor reduces the voltage at the output of the resistor to about 10.2 volts.
 
cruiser54 said:
With it running or just key on?

Too much voltage made the fuel pumps noisy, not too little.
Click to expand...

That is with it running. I had read that the pump has to work harder or trys to draw more current or something when the voltage gets too low. Going to try a jumper wire this weekend.
 
old_man said:
The 87 should have a ballast resistor so the running voltage will not be 12v. Your voltage is within reason. The other voltage is the fuel level signal.

Loud on the pump can be caused by the rubber "stopper" looking thing that is supposed to be on the end of the pump and fits into a bracket in the bottom of the tank. If it is gone, the pump will rattle against the tank with no cushion and will make a ton of noise.
Click to expand...

New pump with rubber "foot" in place. No ballast resistor, so I ASSumed it should be 12+ volts.
 
jrowell said:
New pump with rubber "foot" in place. No ballast resistor, so I ASSumed it should be 12+ volts.
Click to expand...

I would assume somewhere around 12 volts then.

IIRC, the second relay back from the front on the passenger side inner fender is fuel pump. Remove it, clean the terminals, and spray out the receptacle with contact cleaner and see if the voltage comes up.

BTW, do you know the brand of fuel pump you have?
 
cruiser54 said:
BTW, do you know the brand of fuel pump you have?
Click to expand...

Airtex... I know, I know... Never heard anything bad until after I installed it! The reason I put it in was because my Stock one all of a sudden got loud. I thought it was going out so I replaced it. This one does the exact same thing. Starts quite then eventually starts VERY loud buzzing. Turn it off for awhile and restart....and it does the same thing.
 
jrowell said:
Airtex... I know, I know... Never heard anything bad until after I installed it! The reason I put it in was because my Stock one all of a sudden got loud. I thought it was going out so I replaced it. This one does the exact same thing. Starts quite then eventually starts VERY loud buzzing. Turn it off for awhile and restart....and it does the same thing.
Click to expand...

There's your answer.
 
Finally got this figured out. I ordered a Bosch pump and put it my old stock sending unit assembly. Pulled out the Airtex pump and assembly and swapped in my new pump/ old assembly. Turned the key to hear it prime... and nothing... didn't hear a thing. Thought crap, what did I do wrong! Turned the key to start it and it started right up. Can't hear anything from the new pump. It is super quiet! Awesome!

Filled it up with gas and it leaks from where the wires pass through. Not Awesome! The Bosch pump does not fit in the Airtex assembly. Crap! Swapped them back and am stuck with the loud airtex. Anyone have luck sealing that wire area of the sending assembly?

Anyone have a source on a stock assembly? Rock Auto does not seem to have them.
 
Get some fuel resistant epoxy at the parts store, apply it on both sides, let it set up correctly.

Should take care of it.
 
jrowell said:
Finally got this figured out. I ordered a Bosch pump and put it my old stock sending unit assembly. Pulled out the Airtex pump and assembly and swapped in my new pump/ old assembly. Turned the key to hear it prime... and nothing... didn't hear a thing. Thought crap, what did I do wrong! Turned the key to start it and it started right up. Can't hear anything from the new pump. It is super quiet! Awesome!

Filled it up with gas and it leaks from where the wires pass through. Not Awesome! The Bosch pump does not fit in the Airtex assembly. Crap! Swapped them back and am stuck with the loud airtex. Anyone have luck sealing that wire area of the sending assembly?

Anyone have a source on a stock assembly? Rock Auto does not seem to have them.
Click to expand...

I believe Chrysler issued a TSB against Airtex fuel pumps. I don't have it handy but I think it to do with bad wiring sealing at the pump.
 
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