74 911 fuel gauge moves under throttle

[Rick Brooklyn]

So, my car recently had the fuel pump changed. What I noticed now is that the fuel level needle moves up when I accelerate. If doesn't make a big jump, just a little bit, but it's very noticeable. Like it will go from reading a bit less than a quarter full to a bit more than a quarter. Then if I take the foot off the gas it goes back down. Is that normal?

[DRACO A5OG]

Did you do the swap or a shop?

You should see some movement but that does seem allot.

Try a hill as a controlled test, accelerate slowly up, brake on the down side and observe gauge if safe to do so while in motion.

When my reserve light comes on, on hills, it will go off and on depending on position of the car on the hill but my gauge barely moves.

[chris_seven]

If you look at the fuel sender you will see that the float sits in a relatively long tube and this holds fuel around the float.

There is a relatively small hole that allows the fuel to drain out of the tube and if the float tube is full it can take quite a time to drain.

This effectively helps to damp the gauge so it should be quite slow to move.

Have you checked the tank breather?

If this has become kinked you may have a varying vacuum level in the tank and this can cause funny tricks.

[Rick Brooklyn]

Thanks, I'll do the hill test and bear in mind about the tank breather. A very good shop did the swap...

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[Charles Freeborn]

If your '74 still has it's original mounting place (rear) for the fuel pump it's unrelated to the gauge movement. Even if it's moved to the front it should not affect the gauge.
In my '74 the gauge will swing as much as 1/4 of a tank under hard acceleration, braking and cornering (really noticeable on track days) - depending on the overall level in the tank. Like the oil level gauge, best reading is sitting still, on level ground with engine idling. Second best is driving smoothly on level ground. Don't worry about it.