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Discussion Starter #1
I’ve had this problem where the fuel guage will shoot up when I press the brake when the car is not running after I parked my car every time. I remember it used to shoot up slowly. Now it shoots up really fast. It used to slowly go back down when I release the brake. Now it seems like it don’t go down slowly or at all for that matter. The Fuel gage also shoots up when I shut the car off every time brake or no brake. When I turn the key to on position, it resets the fuel guage to the correct position. When I turn the key back off, (after resetting needle, never starting) , it does not shoot up-only shoots up from turning the key off from a running state. I put a new Ac Delco Fuel Sending Unit if that matters. I believe I did a good job. Doesn’t seem like anything was iffy. I’d hate to take out the tank. I’d like to search for this problem. Any help appreciated. Can’t seem to upload videos for some reason. Says it doesn’t support format. Thanks.
 

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I would unbolt and clean the grounds in the left and right kick panels, at the right fender, and at the trunk hinge. The connector to the fuel pump/fuel level sensor also needs to be in good shape.

Search does help sometimes. "Fuel gauge" got me this thread with the trunk ground being the issue:


His solution was to run a new ground wire to the fuel pump plug. When I was prepping my car for sequential turn signals I did the same thing. It is a bit of work.

My theory is that the bad ground back feeds through the park lights and gives some power to the gauge.

The temperature, oil, and fuel level gauges do not return to zero on their own. They will usually stay where they were when the key goes to off. The voltage meter does have a spring return so it goes to low when there is no power.

If you want some theory on the gas gauge look at this thread:

 

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Discussion Starter #3
I cleaned (removed paint) under the 2 left and right trunk electrical grounds and retightened them. I made sure the kickpad grounds were tight as well. I could remove paint and retighten them as well. For some reason, I don’t think that’s the problem as I have jumped grounds off those kickpad grounds and it didn’t make any difference. Maybe I’m wrong and all grounds together, plug connectors at the tank can create this. I unplugged the connector at the tank and looked inside the female sender side. One of the side wires (of three wires) was slightly open more than the two others. If you are familiar with the sender connector female side it is a cylindrical male/female 3 type connector with a slice in the receiver conductor part if you will. I closed the gap/diameter of that one conductor. The fuel gage seems to want to retract a bit faster when I press the brake with the key out. Note: for what it’s worth, The fuel guage level bumps a jitter with car on and I press the brake as well as the other things I explained in the original post. Again, brand new sending unit-AC Delco.**The FSM says something about a ground at the left drivers side tail light by the reverse bulb connector. I’m confused as to what that means? Anyone? Is it relevant to my troubleshooting??~as I’d like to make sure that’s grounded good. Or is the FSM just stating that the ground wire that goes to the sender passes by through the left tail light wire loom and down into the sending unit... How could I test that? If the ground wire comes out the sending unit and around the rear tail light and over the top of the rear left wheel well, where is it’s next stop? Anyway, nothing much to update, as I’m just wiggling around and feeling around and working through other things that may be. Oh yea, here is two pics of my brake light switch which has had an intermittitent “column shifter lock actuator” problem. It’s the actuator that unlocks the gear shifter when you press the brake. Unless that is the unit right next to it. It used to work. I used to get it to work by holding it a certain way. Anyway, when I unplug it my brake lights switch, the brake lights don’t work obviously. And the fuel guage does not shoot up when I press the brake. That fixes it but, lol, no brake lights. Not that I’m asking anything, just tossing info out there for thought or maybe a clue. Only tells me the ground is brake related like we already know. I guess. Anyway, why is there 3 prongs on my connector and only two wires? Is this like this on your cars? Two wires? Was the third for wagons? Anyone? Thanks, didn’t mean to write a book. Hopefully it helps someone someday.——-that splicer repair is mine from long ago. I didn’t purchase a new connector yet. It’s worked so I left it. Rock auto has a two wire and 3 wire connector if I’m correct. Why mine has 3 and two wires has me wondering.
45BCDE63-5C45-4177-945F-6266F011FB63.jpeg
3E74DB75-B922-424C-81D4-1DA74437B1EF.jpeg
 

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Page 8A 14 7
Shows the fuel sender ground circuit
Goes through C 402 terminal A
page 8A 201 36 shows you C402

Then splice S400
Page 8A 14 10 tells you where splice S400 is

Then it goes through pass through P400
Page 8A 14 9 tells you where P400 is
It also references an illustration on page
8A 201 35 illustration #52
On this same page you can see
Connector C406 terminal F in the trunk

Next is the ground to the body
G400
Page 8A 14 9
Tells you where groung G400 is
LT Rear wheel house in the trunk.

Also 8A 202 0 through 8A 202 14 show many of the connector faces

8A 203 0, 8A 203 1 also give an idea,of routing paths
 

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Ground testing , is where Z09B4U and have different but valid methods.
My feeling is that often a questionable circuit will easily carry the load from a multimeter or led test lamp.
It can be misleading

Voltage drop with a high load light is my preference.

My go to is an old halogen headlamp bulb
 

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First to the OP. 95Wagon has again done your homework for you by providing the ground locations, connector locations, and circuit path. By using these points one can do a great deal of testing without damaging the original wiring.

"Ground testing , is where Z09B4U and have different but valid methods.
My feeling is that often a questionable circuit will easily carry the load from a multimeter or led test lamp.
It can be misleading

Voltage drop with a high load light is my preference.

My go to is an old halogen headlamp bulb "

I do not want to derail this thread but for the record I could point to several posts I have made explaining why a test light with a bulb is a better choice than a meter. I think I have suggested on the forum that a headlight is a good way to check voltage drop on a fuel pump circuit. Most of this advice is ignored. So I resort to indirect methodes to get the same information. I recommend disconnecting and reconnecting grounds because few people will take the time to do load testing and voltage drop testing. But they might actually make a better ground connection by just R&R a ground tab.

I personally know people that 95Wagon has spent a lot of time helping, he has helped me directly and by his many good posts. I have never see him recommend anything that would not help.

See the pictures for a example of what happens when a factory plug is not making good connections. The factory fuses do not always protect the circuit. In this case the fuel pump fuse has to have a high current rating to start the pump and may not protect the wiring harness.
 

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[trainTracks]Z09B4U, All good ,we are on the same page.
Comment was more to do with this particular thread.
You are often more on point with this stuff than I [/traintracks]


OP , another thing I am big on is

It is "magical"
Prevents everything, promotes everything else ;)
 

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Discussion Starter #8
I used a halogen lamp to test the ground under the rear left side at connector C 400 on the body harness side. First I gained power from my “disconnected” “missing” “trunk light” wire. I know it’s the trunk light hot wire because it loses power (test light) as I close the trunk. (good or not source of power for ground test, it lights up the halogen lamp. That’s what I’m looking for I guess. I’m sure it’s loading a ground enough for the test, correct me if I may be wrong. Anyway, I connected to the trunk light hot wire, then to the halogen, then off the halogen to a needle probe (homemade👀🙂)... i then used the needle probe and touched the inside of C 400 Contacting Terminal F, “body-harness side” of the connector (black wire) (photo provided). The old halogen 12.6 auto lamp lights up every time. Does this mean my Ground from connector C400 on forward toward the front of the vehicle are all testing good for this issue I am having?

Notes: I removed my rear left tail lense yesterday to clean all the crud out and familiarize myself with that “ground splice near the reverse lamp”. I noticed my far “outside” cornering lamp bulb is blown out. The bulb is charred inside the glass. The right side don’t work either. could this be an indicator of some sort?
D0269281-FC8A-4D9D-A7BB-22AFADEB180E.jpeg
 

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Discussion Starter #9
More information: the inside of the connector (connector contacts) C400 connector look good. And the ground test is good with halogen on both sides of the plug.
 

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Discussion Starter #11
More information: my two front ABS (Anti Lock Brake) short harnesses are missing and my ABS light is on in the dash. The reason why they are off is I have large wheels on my car and the edge of the wheel sliced the drivers one in half against the frame and I removed the other until I purchase the pair. Maybe this is a reason for my guage issue? Just tossing possibilities out there. Thanks.
 

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If the car side ( towards front, with rear side disconnected ) carrys the halogen lamp load then yes the ground circuit to the LR wheel well is fine.
As Z09B4U says though, quick and easy to unscrew, clean, reconnect
Just for fun, what does the fuel guage do
Ign off, 4 ways on
Ign off , tail lamps on off.

Like i said, sit down and really study the manuals.

When checking the car side of C402 A,
Remember to reconnect C400, pay very close attention to the tail and brake lamps to make sure non come on dim.
 

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Discussion Starter #13
Page 8A 14 7
Shows the fuel sender ground circuit
Goes through C 402 terminal A
page 8A 201 36 shows you C402

Then splice S400
Page 8A 14 10 tells you where splice S400 is

Then it goes through pass through P400
Page 8A 14 9 tells you where P400 is
It also references an illustration on page
8A 201 35 illustration #52
On this same page you can see
Connector C406 terminal F in the trunk

Next is the ground to the body
G400
Page 8A 14 9
Tells you where groung G400 is
LT Rear wheel house in the trunk.

Also 8A 202 0 through 8A 202 14 show many of the connector faces

8A 203 0, 8A 203 1 also give an idea,of routing paths
Thanks a bunch for this information you put together here. I didn’t want to respond too much as to confuse anyone else looking at it or me respond some information that is not true confusing somebody else that may read here. I’m barely grasping as it can get confusing when referring to different sections of the book forgetting one link to others. Again thanks-I see what you explained here, it’s helped.
 

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I had a similar issue when I got my car. In my troubleshooting I found there's a large connector in the top of the trunk on the drivers side. So I popped that open and began testing the wiring forward to the fuel gage. And it worked properly. I cleaned all the contacts in that connector and put it back together and from that point on, everything worked properly. Nothing looked out of the ordinary. Car had sat for more than a few years.
 
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