1994 Impala SS fuel pump changed/fuel guage shifts back & forth

[Geo]

I have a question regarding the new behavior of my fuel guage after picking up my car when the new AC/Delco fuel pump was installed. The strainer and the fuel filter were done as well.

The fuel guage is flipping back and forth at random intervals now. I haven't seen it do that since the one time, years ago, in the 90s, when the fuel pump NEEDED to be changed.

It was getting late and the techs at the dealership had left for the day or I would have driven back. I will go in soon, but, thought to talk about it here first.

It also noticed that pumping the brake pedal instantly makes the fuel guage shift. It will shift to the left when I hit the brake pedal and then go back again when I let go of the brake pedal.

I figured perhaps it is a grounding issue and/or shoddy installation of the fuel pump to the factory wiring harness.

Perhaps it's a faulty fuel pump (with respect to the float or the sender). The car is performing awesome otherwise, with the rear tires breaking loose at the touch of the throttle in the dry so the delivery of fuel is not sacrificed.

I've just changed the battery to a brand new one as well and it's still doing it.

Before I changed the battery, the other guages were somewhat affected by the braking action and the headlights would dim too, but it was a really old battery. Now, at night, I am only noticing the fuel guage being affected by the brake pedal. It can't be a coincidence as the fuel pump was just changed.

Any thoughts?

[Darigaaz]

Been a while since I've been over to Naisso but from what I remember there could be an issue with the sending unit and it needs to be replaced or refurbished. There was a step by step guide on how to do it over in the Naisso forums but I haven't messed around over there in a long while.

[RubberCtyRauder]

Video shows prolly whats happening, responses include replace sending unit..other google search turns up same. a common GM issue at the time frame.

https://www.youtube.com/watch?v=tImDK4x2uyU

[Geo]

interesting

the sender unit is part of the fuel pump yes?

the fuel pump was just changed, I'm thinking the warranty on the work should entail the GM dealer to fix this issue.

[Geo]

so then what are the odds it's faulty wiring on the GM dealer's work, when they installed the fuel pump (bad ground for example or something intermittent with the wiring on the wiring harness, between the fuel pump and the wiring harness), or, that it's the sender?

the GM dealer says it's possible that it is their wiring job, but, that it could also be the sender which is a separate unit that goes into the same space in the tank where the fuel pump is.

I said that the guage wasn't acting like this before the fuel pump job. They said that it's possible the sender is flawed now coincidentally or not so coincidentally. He (the shop foreman) said that it's possible the sender was "disturbed" while they were doing the work but that S@I& happens and that if so they deem the sender's failing not their fault.

He said that they are willing to pull the tank and inspect the wiring but if it's not the wiring and it's the sender that I would have to either pay for a new sender or bring in my own supplied part from a speedshop.

I know the guage fluctuating could mean a bad sender (which was fine before the work started) or it could be wiring but in all likelihood, if it's the wiring, is it more likely the ground in the trunk area or the wiring harness connection to the fuel pump?

I just have the feeling they're going to tell me that it's the sender after they dig in their and rip apart the work they just did.

[BLACKMARAUDER04]

Most fuel pumps come 2 ways. the pump itself or with the 'hat" which includes a new sending unit.

I replaced the entire hat on my 1999 Sable recently as the sender unit was
probably not working properly either..

[Geo]

according to the foreman, the AC/Delco fuel pump I supplied doesn't have a sender or float in it.

The EP376 AC/Delco fuel pump looks like this
http://www.ebay.com/itm/AC-Delco-EP376-Fuel-Pump-25163464-Impala-SS-Caprice-Corvette-Roadmaster-NIB-/390624396949

here's page 3 of a good forum discussion on the sender's old design vs. the new AC/Delco design
http://www.impalassforum.com/vBulletin/showthread.php?t=232378&page=3

the sender unit could be FLS1072 or FLS1020