Fuel/Gas Gauge Problems & Questions

hey im new to the boards , just got reffered by another board because it was not active and im in a irritating situation.

long story short from other board....

Quote :

My fuel gauge shows that it is full... all the time. the car has died on me numorous times. it goes down when i cut the car off , but soon as i start it , the gauge zooms to full.

i was told that it was the fuel sending unit. i just replaced the unit today , cut the car on and it still reading full! besides money down the drain , what is wrong with my car!

after getting some suggestions i "tried" to check for a bad ground wire or short , but wasnt going well. i didnt even know what i was looking for.

so i took it to the shop..

Quote :

i went to a shop and had them look at my car for 90$ to look for the short. they said the fuel sending unit wasnt getting a signal from the fuel gauge and that the wires were all good and grounded around the fuel tank....

for 150$ more they were gonna to take off the dash and search some more. they said they needed 2 more hours :/ ... so im going to pay the 150 next weekend minus the charge there going to charge to fix it! , if i cant find a way to do it myself.

what wire might i be looking for around the dash? and if its not around the dash area where else might it be?

Have u tried to ground the black wire at the sending unit by sticking a paper clip or sumin into it and touching sum metal around the tank?

Verify the fuel sending wire AND the grounding wire.
I've learned that pretty much every GM vehicle from the late 80's to present has the same fuel indication setup (0-90 ohms) that uses a very small purple wire for the fuel level signal.
I have yet to check this out on the riviera, but it should be the smallest purple wire in the smallest wire bundle at the driver's side sill (under the carpet). I can't recall exactly as I have been messing with too many buicks ...

Confirmation of correct wire:
Once you think you've located the correct wire in your Riviera I would normally advise you to cut it with 1/2 tank (or less) of gas. If it's the correct wire, the fuel gauge will go from 1/2 tank to extreme full. If it does not, that was the wrong wire Repair the cut wire and try again.
Of course, I think your wire may be damaged, so try to verify if it is cut/damaged. It could severed anywhere, or it could be the ground (more likely.) I just looked at your pictures on regalgs.org. I am referring to the small purple wire you can see in the picture.

I was recently thinking of curing the inacurate fuel gauge on the riviera by adding a potentiometer to the wiring. Although quite easy to do, it's fairly low on my priority list.

What year Riv, and what engine?

My gauge works fine until about half a tank it pretty much doesnt move. Then when you are actually close to empty, it will say totally full or totally empty depending on how it feels at the time. I think its the in tank sender so ya thats not going to get fixed unless the pump fails. I don't have that kind of time or money right now so I deal with it

turtleman wrote:

My gauge works fine until about half a tank it pretty much doesnt move. Then when you are actually close to empty, it will say totally full or totally empty depending on how it feels at the time. I think its the in tank sender so ya thats not going to get fixed unless the pump fails. I don't have that kind of time or money right now so I deal with it

He put a new sending unit in.

Why are they taking apart the dash? The fuel sending unit is in the tank.

Just like everyone is saying it is the float/ sending unit. The fingers that make contact with the resistive PCB in the tank can fail. They would make partial or no contact. I bought a new sending unit and installed it works great now. I will post pictures.

If some one needs a sending unit I have a spare one. I bought one and misplaced it. Then I bought a second one. I also have the J-tool to open the lock ring on the tank.

Could the sending unit also cause the guage to read inacuratly? Like mine says it is more full than it really is until about a quarter tank when it drops down to a more realistic reading.

I've learned to live with my screwed-up fuel guage.... Fill-er-up, and the guage reads full, and never leaves there for about 100 miles. Then drops like a rock.

Mine's been acting basically the way Duffy describes since the car was new. Sitting at full for a while is normal if the fuel level goes above the range of the sensor. After that, the time it takes to get to 1/2 seems to be longer than from 1/2 to "E".

duffy wrote:

I've learned to live with my screwed-up fuel guage.... Fill-er-up, and the guage reads full, and never leaves there for about 100 miles. Then drops like a rock.

haha ive seen that consistently in all GM cars around this decade

Jason wrote:

Verify the fuel sending wire AND the grounding wire.
I've learned that pretty much every GM vehicle from the late 80's to present has the same fuel indication setup (0-90 ohms) that uses a very small purple wire for the fuel level signal.
I have yet to check this out on the riviera, but it should be the smallest purple wire in the smallest wire bundle at the driver's side sill (under the carpet). I can't recall exactly as I have been messing with too many buicks ...

Confirmation of correct wire:
Once you think you've located the correct wire in your Riviera I would normally advise you to cut it with 1/2 tank (or less) of gas. If it's the correct wire, the fuel gauge will go from 1/2 tank to extreme full. If it does not, that was the wrong wire Repair the cut wire and try again.
Of course, I think your wire may be damaged, so try to verify if it is cut/damaged. It could severed anywhere, or it could be the ground (more likely.) I just looked at your pictures on regalgs.org. I am referring to the small purple wire you can see in the picture.

I was recently thinking of curing the inacurate fuel gauge on the riviera by adding a potentiometer to the wiring. Although quite easy to do, it's fairly low on my priority list.

thanks for your input , im going to check it out today. and for the record , how would i go about repairing wires? , because i noticed that some of the wires on the fuel pump connector have the plastic covering broken off but the wires arent coming out of them

turtleman wrote:

duffy wrote:

I've learned to live with my screwed-up fuel guage.... Fill-er-up, and the guage reads full, and never leaves there for about 100 miles. Then drops like a rock.

haha ive seen that consistently in all GM cars around this decade

My bonnie does it, but much worse. I have ran out at about 1/8 a tank. The riv is only a little better as most cars, the gas needle will actually accuratly read empty, the Riv will stay a little above that making me think I can easily make it down the street to the gas station, nope...

Are we talking about an inaccurate guage or the thing where it bounces between FULL and what ever the real fuel level is? If it bounces then your sender in the tank is going.

As for inaccuracy, I agree. The guage is very non-linear. The first and last quarter are really slow. It seems to zoom from .75 to half tank.

Inaccurate. So that is just characteristic?

When I put 10 bucks of 94 in at almost 3bucks a gallon there is no way it is even near a half a tank, but it reads half a tank. Until it flies down to a 1/4.

No "fix" for this?

If his gauge is ALWAYS on full when the car is on (not bouncing, which would indicate a problem with the sender), he is getting a resistance > 90. That's why I suspect a damaged wire. It would give an infinate resistance.

Quote :

how would i go about repairing wires? , because
i noticed that some of the wires on the fuel pump connector have the
plastic covering broken off but the wires arent coming out of them

Depends what it looks like. If you find the damaged area, cut and solder, or splice in a small section of wire if the damage is extensive.

As for the fix for the INACCURATE gauge, as described by Aaron and Duffy, is easily fixable. I described how in my above post. It's just I haven't had time to do it yet. Maybe one day I'll get a write-up done on that, but if you think that fixing a slightly inacurate fuel gauge takes priority over installing rockers, headers and gears in the roadmaster or alky injection in the TR, you are wrong
The fix essentially addresses the "top" half of the gauge by adjusting the "complete full" needle position. It isn't garanteed to fix the lower portion, but it should.

update: i took it to the shop and the conclusion is that i have a bad dash cluster , and said its easy to change it yourself . so i seen a used one coming from the same year rivi as mine for 24.95 plus s/h. should i get it? and what other dash clusters will fit on my 95' rivi

24.95 sounds really cheap.

When i turn the car on, the fuel gauge runs up to full. It stays there. I've come suspect the float or level sensor. So i read that the sendin unit might need look over. Where exactly is the sensding unit? how can i gain access to it? pictures would be awesome!

Yes, yes, i know, i need to put up pictures. i'm working on it.

pull your trunk liner out...theres an access panel up near the back seat...cant miss it!

Related thread from Series I forum, might help:

https://rivperformance.editboard.com/Supercharged-3800-Tech-c2/Series-I-Engine-Transmission-f13/Fuel-Gauge-Reads-Full-Dilemma-t617-0.htm

something weird happened today. When i was taking her in to the paint shop. The needle did it usual thing. Went up to full and came down to 3/4 and slowly went back up to full. It did this twice. Each after starting the car up. The second, though, only got down to 7/8 full before it slowly climbed back up.

Any thoughts on this?

sounds to me like a bad wire....my Lesabre T Type did this with the temp guage...an i could smack the dash an make it move...an it was due to a faulty guage wire...common on those things...

I could also be a bad fuel level sender. There are little contacts that run on a resistive PCB. The fuel level is determined by the resistance. When the contacts wear out or break you will get an intermittant resistance. Then the fuel level will bounce around randomly.

I think I have an extra sender if you end up needing one.

i should have the car back by this weekend. I'll try and figure out which way i need to go. Thanks for the offer. I'll let you.