Fuel pump help!!

[beto101]

Im having problems with my fuel pump. Ive done a 2003 5.3 swap in my 80 K5. I got the fuel pump assembly from same donor vehicle and truck ran for some months. First fuel pump went out. Got another used pump from my buddys wrecking yard and once again was mobile. Few weeks went by and pump went bad again. Noticed sending unit had burn marks where connector is on top of sending unit. im now planning on buying a new fuel pump. My question is how many volts should I have at fuel pump?

 

[DeviousK5]

Battery voltage. When the relay is on , which by now I'm betting you found out is only for a few seconds(3-5) after the key is turned to run. If you have a good scan tool you can turn on the relay and it will stay on til it times out.

As for the burn marks, they re-designed the pump/float connector . A new pump should come with a new shaped connector(rectangle vs the old square shape). That you will have to splice in. Do yourself a favor and save the heatshrink covered butt connectors that should come with the new pump and do a good solder/heat shrink job on it.

 

[texas4x4rebel]

Spend the money and buy a walbro pump.

 

[beto101]

yeah ive already have a pump picked out. i just dont know why pumps keep going out. i will check and see what voltage i have at pump connection. could my fuel pump relay not be letting enough power go to pump or possible too much power? any other ideas why pump could be going out. ive changed sending unit with a new one, new wires from fuse box to fuel pump.

 

[k20]

too little voltage or a bad ground would be my first guess. After that Im stuck with a fuel system problem, restricted return line or a clogged filter perhaps? Electric pumps are cooled by the fuel flowing through them, maybe its keeping the pressure up but not flowing & cooling itself?

 

[beto101]

Ive remove return line at the tank and no fuel. Disconnected at fuel rail and same no fuel. Very little fuel comes out when engine is warmed up but cold it starts up good. I have halfa tank of gas on 31 gal tank.

 

[k20]

what kind of fuel pressure readings are you getting?

 

[beto101]

I have to get a pressure gauge then repost.

 

[beto101]

does it makes a difference if my 5.3 is a flex fuel engine?

 

[texas4x4rebel]

Are you using the complete plastic sending unit out of the 2003 and no the flex fuel engine dosent make a differance with your pressure.

 

[beto101]

No im just using the module. i bought the sending unit for a 87 k5 blazer and the fuel tank from a 87 blazer. All my fuel lines are from a 87 up suburban so they are all prebent and have no kinks. Fuel filter is clear. New lines from filter to manifold. Ive replaced pump 3 times now and seems to be doing the same thing. It would start losing pressure till it gives out.

 

[Fordum]

Unless you have an old military truck with a 24 volt system, you cannot get too much voltage to the pump. It runs on full system voltage.
Of course if your alternator voltage reg went bad, you would get too much voltage, but you would be having lots of other problems by now.

The main ways to ruin one of those pumps is:
Running it dry.
Low voltage.
Stopped up lines.

If the return line and all the filters are clear, and you don't make a habit of sitting there turning the key off and on with an empty tank, then odds are its a voltage situation.

Remember there are two halves to the power situation for that pump.
Battery voltage and ground.

You can have full battery voltage going to the pump. but it it does not have a good ground, its seeing low voltage.

I would take a long hard look at those burn marks. Even if they are not a symptom of your problem, you really don't want to have arcs around a gas tank.

Then, check the ground. Some car gas pumps have a separate ground wire in the plug, but most of them ground to the tank.
If you do not have a good ground from the truck to the tank, you will burn up the pump.

Look at one of your old pumps. The motor has to have two wires. If you only see one, the other is grounded in the motor, If you see two, see where they both go. If one goes to the frame of the assembly, then that frame has to have a good ground back to the battery somewhere.