lovmy90vette

I have a 1990 coupe and the digital gas gauge generally shows the tank full od fuel even when the tank is close to empty. A chevy dealer once told me that the fuel pump and sending unit is inside the gas tank and to fix this would be about $800.

Is there a way to verify what the issue is with the gas gauge not registering correctly?

FASTAZU

Most likely the assembly will have to come out so you can see whats up, could be a stuck float assy. or the tank inner cell wall interfering with the float.

John A. Marker

Whole assembly....remove your fuel pump and transfer over....

http://www.rockauto.com/catalog/x,ca...,parttype,4436

Easy fix....if you have never changed out the fuel pump....allow yourself 1 hour.....

antfarmer2

easy fix dealer is ripping you

aklim

There is a way. You are in MI, correct? Aren't you ready for a shutdown of the Vette? If not, wait. If so, put it inside a WELL VENTILATED garage after you ran the fuel tank as low as it will go. Take the pump unit off and turn the key to run. Have someone watch as you move the float up and down slowly and see if it changes. If not, you have a bad sender.

Cliff Harris

An alternative source of information:

https://www.corvetteforum.com/forums...h-article.html

whalepirot

Having just done this, I found that article lacking to restore proper readings in my car. My DVOM showed a slightly varying, but high, reading upon completion of the above, so the gauge would indicate mostly full.

This is the in-tank variable resistor- the winding and fragile contact:


Top center is one of two wires from the sender. I cleaned both where they plug into the assembly's mount, using DeOxIt contact cleaner, sliding the pin on and off to scrub.

The half-arc inside the D-shaped case is the rather delicate winding, a variable resistance created via more wire between the contact's position on it and ground. The delicate spring contact is to the right. Look closely at this, and the sharp eyed will see a dab of solder. Cleaning it was fine, but the problem remained. I found it by checking all resistances between components.

The culprit was the brass contact's poor connection to the springy U-shaped portion attached to the sender's arm. The dash 'sees' total resistance in the circuit and any extra along the way will drive the gauge towards full.

Using my solder iron, a nice dab of flux paste o clean the brass on both sides, I applied that small dab of solder.

Now the circuit resistance varies for the first time in many years, from near 0 ohms, to around 125. I tested it before reinserting the assembly into the tank as verification and was surprised to see how slowly the bar graph displayed moved, when the float arm did.

I also chose to bend the float arm slightly so the float bottoms out 14" below the mounting flange, as the tank measureds. It was full-down at 14.5" so the tank would show fuel remaining, when there was none.

Only a drive or three can verify if that was a mistake.

Now, I get to relearn what F and E means in real life!

aklim

A question. IIRC, m7 89 XR4Ti had a "delay circuit" that would cut off the feed value quantity. Not sure how to explain it but basically, even if it reads 1/4, it takes a bit to display it. On my 01 Ford Excursion, it does the same thing. I fill up 44 gallons of diesel, come out after paying and taking a leak and it is only at about 3/4 tank and I start filling up when it is about a while after "E". The way I was told was that if it responded quickly like the older cars did, every time you go round say a right turn, your 1/2 tank would ready 1/4 and if you go round a left turn, it would go from 1/4 to say 3/4. So this delay gives a better feel as opposed to rapidly changing gauge readings. Not sure if I am making sense due to poor explanation.

"F" means you drive for a while. "E" means that if you drive too long, your Chevy becomes a Ford.

Found On Road Dead
Driver Returns On Foot

whalepirot

It's called smoothing of the data stream.

gerardvg

Hi

Is an easy job to remove the fuel sender unit, in my case I found the tank had started to collapse.. The wall of the tank was sucked inward stopping the float from going down, kept showing full.

I bent the sender float to clear it, popped the tank out but it had done it again. Will replace the tank and check the charcoal canister and valve at the same time. Something is obviously wrong. You really need to remove the sender and have a look and feel. Then try remove the gas smell from your arm lol

The little woman hates gas smells ...

lovmy90vette

Hey, thanks so much all of you for the info to fix my gas gauge. The video was great especially cuz I am not the best mechanic. So if I replace the "whole Assembly" is that the same as the Fuel Tank Sending Unit that costs $211.79?

antfarmer2

make sure it comes with the pump

aklim

I would rather it didn't. I'd have a Walbro pump in it and replace the dampner if it were me.

lovmy90vette

John,
So if I just buy this new Fuel Tank Sending Unit for $211, that's all I need to do? - John White

aklim

I don't see a pump so you will have to transfer it over or females a Walbro pump yourself

thecatmac

I just bought one for my 85 about a month ago from rock auto. It is the entire unit, don't need anything else. Real easy fix! Just do it!

aklim

At least, I'd take the damping thing out.

Also, if the screws aren't stainless, I'd get SS bolts. The PO decided to use some regular crap and I had a hell of a time getting it out.

lovmy90vette

Thanks again for the info...... the vette is in storage for the long Michigan Winter but plans are to work on this in the Spring.