Proper voltage range for fuel pump

[CFI]

With the pump running:
Put your negative lead on the battery (-) and positive lead on the pump's ground wire. Record.
Put your positive lead on the battery (+) and negative lead on the pump's feed wire. Record.
Add together.

EDIT: The .78V you got earlier would indicate a problem on the ground side. (According to Chevy manuals anyway;-)

Ok I did those tests.

Engine running:
Negative to battery, positive to pump ground= .82
Positive to battery, negative to pump feed= 1.27 to 1.5

[Bitsyncmaster]

Ok I did those tests.

Engine running:
Negative to battery, positive to pump ground= .82
Positive to battery, negative to pump feed= 1.27 to 1.5

So your dropping a little over 2 volts in all. If you do my modification where you cut the ground wire on the inertia switch and run that switch pin to frame ground you will gain about 0.3 to 0.4 volts (less drop on the ground). That will also bump your volt gauge up the same amount when the engine is running.

[Ron]

Ok, you have a ~2.2V drop at the pump, with everything in the circuit connected. So it's getting ~14.2V (good) minus 2.2V = 12.0V, which meets the newer pump's voltage requirement.

Should of asked to begin with but are you just curious or having a problem with it??

EDIT: +1 Bitsy

[CFI]

So your dropping a little over 2 volts in all. If you do my modification where you cut the ground wire on the inertia switch and run that switch pin to frame ground you will gain about 0.3 to 0.4 volts (less drop on the ground). That will also bump your volt gauge up the same amount when the engine is running.

Will do, thanks.

[CFI]

Ok, you have a ~2.2V drop at the pump, with everything in the circuit connected. So it's getting ~14.2V (good) minus 2.2V = 12.0V, which meets the newer pump's voltage requirement.

Should of asked to begin with but are you just curious or having a problem with it??

EDIT: +1 Bitsy

Thanks. Just bored and running some tests I’ve been curious about.

[David T]

My guess on why the pumps burn out (the original style) is that either the screens get plugged up and/or the pick-up hose gets kinked or collapses. Running the pump dry (without fuel moving in and out) causes it to run hot and with no lubrication, the gears inside get worn quickly. The pump gets very noisy and starts to draw a lot more current. The excessive current causes the windings inside the motor to overheat and short out, killing the pump. While that happens you also wind up melting fuse #7 out of the fuse block. My cure is to install a spring inside the pick-up hose to prevent it from kinking or collapsing from the suction.

[CFI]

My cure is to install a spring inside the pick-up hose to prevent it from kinking or collapsing from the suction.

I did that on my old setup after the pump got noisy on a long drive. It worked great.

[ritztoys]

If you do my modification where you cut the ground wire on the inertia switch and run that switch pin to frame ground you will gain about 0.3 to 0.4 volts (less drop on the ground). That will also bump your volt gauge up the same amount when the engine is running.

I did exactly this mod as suggested by Dave last fall, I was very happy with the results and the voltage to the gauge was much better.

[cis6409]

Just as interesting side note I forgot to mention, that I only found there was an issue with the pump voltage when I was doing a power run on a dyno test.

When this test was being conducted, the dyno guy had to stop the power run when it got to near the top end higher rpm. The fueling dropped way off the charts. He immediately stopped the power run and explained a couple of issues that on his experience what that usually pointed to. After checking the other suggestions they all checked out, it left only the the pump.
The fuel pump was not able to match the required demand at the higher engine loads. He then asked me if the pump was old, and I said no it was only 6 months old at the time. He suggested checking the power supply.

After cleaning up the connections and increasing the voltage the power run was able to be completed safely the next time.

Shane

[David T]

Interesting that it showed up in that manner. Not unexpected, just unusual to find it that way. Typically the pump gets really noisy on a hot day after running for a while with less than 1/2 tank of fuel.There was a story a while back of a group of Deloreans on a cruise and they got to a ferry and had to wait a while. Almost all of them had noisy fuel pumps. It was hot and they had less than 1/2 tank of fuel. Once the pump gets noisy you can figure it is going to die soon. You have to figure if you don't provide enough electric power to the fuel pump, it can't pump enough fuel to the motor. What kind of HP and Torque did you see on the dyno?