Broken Fuel Guage/ New Fuel Pump and Still Not Working

[Bravada 97]

I have a 97 Bravada that overall is in great shape. It has 93k miles on it and runs excellent except the fuel gauge is out to lunch. It was like this when I bought it and the needle is always way past full even when the tank is near empty. I know this is a common problem and it is probably the fuel sensor in the fuel pump.

Well yesterday I dropped the tank and put in a new fuel pump in hopes of fixing the problem. I put everything back together and the fuel gauge is still not working. It will at time drop down to the correct level on the gauge but only for a second or two before going back to the full mark and staying there. I thought a new fuel pump would fix this. What gives? Any info would be greatly appreciated.

[blazes9395]

This is a fuel level sender problem. Its the thing that looks like a float, on the other end of the float is where the contacts that tell the fuel level inside the tank. Those contacts wear out, corrode, and you get the dancing guage problem. You were so close when you replaced your pump, it was right at your fingertips. Solution? Pull it all down and replace that sender.

[mike2004tct]

Originally Posted by Bravada 97

Well yesterday I dropped the tank and put in a new fuel pump in hopes of fixing the problem. I put everything back together and the fuel gauge is still not working. It will at time drop down to the correct level on the gauge but only for a second or two before going back to the full mark and staying there. I thought a new fuel pump would fix this. What gives? Any info would be greatly appreciated. As it stands I will never own a GM vehicle again.

Did you replace just the pump, or the whole assembly with the level sensor attached?

If you put a whole new assembly in, I'd suspect you don't have the gauge connector on properly, or a bad connection. The gauge will default to way past full when no power is getting to the sending unit. You'll have to lower the tank partially to check it.
There's a 3 wire connector going to the sensor unit thru the top of the assembly. A power, Ref. signal, and ground wire. Make sure none of the connectors are corroded. It would even be helpful to put dielectric grease inside the conn. housing. The pump should have come with the grease, as corrosion is a known problem on 4 door units.

[Bravada 97]

Thanks for the reply guys. I replaced everything. I took out the old pump float arm, ect and put in an entire new assembly. Today I was out driving and the gas gauge actually stayed in the proper place "1/4 tank" according to the computer readout on the upper windshield. But after about 6 miles or 10 minutes of driving in town the gauge jumped up to the 1/2 tank mark and stayed there even though there was only about 4.5 gallons of gas in the tank. I guess 10 minutes of it working properly is better than the 2 seconds from my first post. I will try reconnecting the 3 wires and see if that helps fix the problem. I have to think the float arm is in correctly as it snapped into the slot on the pump very tightly and didn't have any play in it before I put the fuel pump assembly back inside the tank.

[Bravada 97]

It has been a few days now since I changed the pump and I noticed a trend starting to happen. The gauge is accuarate when I drive the vehicle for the first time each day. After about 5-10minutes is when the gauge starts to climb up back towards the full mark. Odd.

[old_master]

A poor ground for the fuel level sending unit will produce the same symptoms, (dancing needle). A poor ground will increase resistance and shorten the life of the fuel pump also. The fuel pump and fuel level sending unit are grounded at the same point on the vehicle. The ground on a 4 door is on the rear crossmember. The ground on a 2 door is at the frame rail very close to the filler neck. Remove the bolt and clean the terminal and the frame with sandpaper, a wire brush, or a file until bare metal is visible.

[mike2004tct]

Originally Posted by old_master

A poor ground for the fuel level sending unit will produce the same symptoms, (dancing needle). A poor ground will increase resistance and shorten the life of the fuel pump also. The fuel pump and fuel level sending unit are grounded at the same point on the vehicle. The ground on a 4 door is on the rear crossmember. The ground on a 2 door is at the frame rail very close to the filler neck. Remove the bolt and clean the terminal and the frame with sandpaper, a wire brush, or a file until bare metal is visible.

That is not correct. The ground you're talking about is the static discharge ground strap (stops sparks from occurring during fueling when the hose touches the filler neck). The fuel pump and level sensor ground wires are in the harnesses and terminates somewhere inside the cab.

The fuel pump has it's own separate connector, which does pretty much the same thing, except it most likely grounds somewhere around the EMM under the hood.

The fuel pump assembly is plastic. There's a rubber gasket that also shields the pump assembly (plastic) from the tank. There is no ground from the pump or level sensor directly to the tank.

[old_master]

Originally Posted by mike2004tct

That is not correct. The ground you're talking about is the static discharge ground strap (stops sparks from occurring during fueling when the hose touches the filler neck). The fuel pump and level sensor ground wires are in the harnesses and terminates somewhere inside the cab.

Unless 97 is different than 98, the fuel level sender and the fuel pump both ground to the frame near the filler neck on a 2 door, and to the rear crossmember on 4 door models. The static strap has its own separate ground.

[mike2004tct]

Originally Posted by old_master

Unless 97 is different than 98, the fuel level sender and the fuel pump both ground to the frame near the filler neck on a 2 door, and to the rear crossmember on 4 door models. The static strap has its own separate ground.

I Can't speak for the '98s, but I've had my '97 apart 4 times, as well as my '96 Pontiac, and the fuel pump assemblies are the same. They're a housing made of plastic, with connectors on the top side. The assemblies have no metalic (ground) mating surface to the fuel tank. All of the grounds run through the connector housings towards the front of the vehicles to be grounded at some unseen point.

On my '97, the ground strap on the filler neck connects at the bottom end of the filler neck, and goes to the frame rail. At the bottom end of the filler neck, there's a short piece of rubber hosing, connecting the filler neck to the tank. This creates another isolator such that the filler neck itself is not connected (grounded) to the tank. The tank itself isn't even grounded to the frame. There are felt isolation pads (strips) lining both the straps that hold the tank up, and pads along the top of the tank where it meets the cargo area floor. The tank is completely isolated, and ungrouded.

I would suspect the '98s are much the same (looking at pictures of the pumps, they look identical to the '97 assembly)
Here's a pic for a '98 assembly. You'll notice all of the contact points are isolated by either plastic or rubber.


On my '04 Chrysler, the whole fuel tank is plastic, and the fuel filter is inside the tank.

[old_master]

The question is not whether the tank is grounded, it's not. The connector at the pump module has 4 wires: A feed and a ground for the fuel pump, and a feed and a ground for the level sender. The two ground wires, (at the module connector), run to a splice pack, along with several other ground wires. From the splice pack, one wire goes to the frame. If that connection is not clean and tight, resistance will increase causing the fuel gauge to read high or erratically. High resistance in the fuel pump ground circuit will shorten the life of the pump. Varying the resistance to ground is how the level sender operates, therefore it's far more sensitive to excessive resistance than the fuel pump. A poor connection in the level sender feed wire, a poor connection at the module, or a poor ground are all likely things to check, (it's not likely that both level senders have the same problem). I'm not trying to get into a pissin' match here, merely giving the original poster things to check as possible causes for his erratic fuel gauge operation.

[mike2004tct]

Originally Posted by old_master

I'm not trying to get into a pissin' match here, merely giving the original poster things to check as possible causes for his erratic fuel gauge operation.

As you will notice, I've already said the possibility exists for a bad connection somewhere in the connectors or their wires. I agree it's most likely in one of the harnesses, most likely the white square connector in the above picture, the level sensor connector.

This is a known problem on '97s. replacement pumps from Carter, Master, and Delphi come with dielectric grease to load inside the connectors for the 4 door units, but not the 2 door units. I alluded to that above also.
Perhaps it's a corroded pin in the harness.

Look very closely at the pciture I posted above. The pump, and the level sensor each have their own connector. Each connector is a 3 wire unit.
That, by the way, is a '98 pump. The 97 pump assembly is identical.
I also mentioned what each of the 3 wires are for in a previous post.