[Patina Tiger]

Yes,

It is the little retainer cap that is on the underside of the sending unit, electrical current gathers corrosion there due to air exposure in the tank over the years. Carefully pry off the cap and clean the brass fitting and thin metal strap. After done, set the unit in the trunk, (for ease of testing), and ground with key in the RUN position then move the float arm up and down for reading. Should be good, then install into tank.

Alex

[Greg Reid]

And from what I've been reading here on the forums, it's worth fixing. I understand that a lot of the new units bought at the parts stores are failing within a year or two.
These originals last 40 years easily.

[geiser]

I have been doing quite a bit of reading and have a simple question. Does the center trunk body plug line up with the sending unit?

I put in a new sending unit and tank early in my rebuild process (before the dash was in.) I found the harness was not connected on either end in the trunk after the dash was put in. I currently have a full tank. I really don't want to drop the tank to connect the harness and was hoping to pry the body plug open to connect/fish the harness to it.

[lazlo]

Originally Posted by "QUICK-SILVER"

Grounding the sending unit wire in the trunk, should make the guage go to empty.
Try it and see what happens, that'll really narrow things down.
Straight to ground want hurt it, same thing the sending unit is suppose to do at empty.

If it does bring the needle back down, sending units in trouble or tanks lost its ground.

Check it out, post back, and we'll go further.

Are the straps what ground the tank to the car? I am on my second sending unit from Summit and neither shows above 3/4 tank when it's full. Replaced the sending unit because the original developed a leak around the outlet tube. The gas gauge worked fine with the original unit. It doesn't seem to like these Taiwanese sending units. This is on my 1966 Lemans. Any thoughts?

Tomorrow I'm gonna take the original to the radiator shop & see if the can fix the leak..

[Greg Reid]

Originally Posted by lazlo

Are the straps what ground the tank to the car? I am on my second sending unit from Summit and neither shows above 3/4 tank when it's full. Replaced the sending unit because the original developed a leak around the outlet tube. The gas gauge worked fine with the original unit. It doesn't seem to like these Taiwanese sending units. This is on my 1966 Lemans. Any thoughts?

Tomorrow I'm gonna take the original to the radiator shop & see if the can fix the leak..

Did you check the resistance of the unit? Should be 0~90 ohms full range. This is what controls how far the gauge will move up and down.
The tank itself doesn't really have to be grounded for the circuit to work. The sending unit ground wire is grounded with a screw to the trunk pan. The rubber gasket isolates the unit from the tank, more or less. The positive lug on the sending unit gets the hot wire and it must be isolated from ground but that's built into the sending unit.

[lazlo]

Originally Posted by Greg Reid

Did you check the resistance of the unit? Should be 0~90 ohms full range. This is what controls how far the gauge will move up and down.
The tank itself doesn't really have to be grounded for the circuit to work. The sending unit ground wire is grounded with a screw to the trunk pan. The rubber gasket isolates the unit from the tank, more or less. The positive lug on the sending unit gets the hot wire and it must be isolated from ground but that's built into the sending unit.

Went thru this a couple of years ago with my 71. It worked with the original sending unit but not with the two Taiwanese replacements. I've had it apart three times now. I didn't think the tank needed to be grounded but wanted to make sure..

[lazlo]

The original sending unit has been repaired and the ohms check at 1.2 at the bottom and about 87 at the top. After the holidays I'll be putting it back in...

[Greg Reid]

You should be good with those readings and that original unit will probably last you for a very long time.

[lazlo]

Summit racing sent me the Original Parts Group sending unit part # OPGPZ00732. It did not work properly. I complained & was told by Summits tech that I needed to bend the float to make it work. I argued against that ( How many times do I need to bend and install before it works correctly). Summit Racing sent me a second unit & took the first one back. I installed the second unit and it did not work properly...

I got the original sending unit soldered so it wouldn't leak, bought an ohm meter and checked it. low end was just over 1 high end was 85-86. I reinstalled the repaired unit & my gas gauge is again working.

Checked the ohms on the second unit Summit Racing sent me after I removed it from the car. The high end was 80 ohm which read 3/4 tank of gas when the tank was full..

Conclusion... the Taiwanese sending units are junk and you can't depend on a straight answer from the company tech who not only told me to bend the float in an attempt to make it work, but added that he was not aware of any problems or complaints with the sending units..

[bsblguy]

Might as well throw my 2 cents in too. My '69 GTO I replaced the sending unit as well as the tank. Original tank leaked, gauge did not read correctly. On my 2nd one from NPD ( they have a warehouse local ) and still does not read correctly. Full tank reads at 3/4 tank on gauge. With tank full disconnected brown wire inside trunk and checked ohms to ground thru sending unit and had 98 ohms. Grounded wire and gauge reads empty, ground removed and it reads full. Checked ohms from wire to gauge to ground and have 43 ohms. Don't know what that should be. With 98 ohms from sending unit it should read full not 3/4. Anyone know what ohms thru gauge should be?

[lazlo]

new project new questions. I am working on a 71 Lemans Sport convertible. The gas gauge is pegged on full. I started out by disconnecting the ground strap on the tank, sanding & cleaning the contact point and the clip on the wire. Re assembled with new washers.

I disconnected the tan wire in the trunk. Grounding the wire to the gauge caused the gauge to go to empty. Unhooked the ground and the gauge went back above full so the gauge is working.

Put an ohm meter on the wire to the sending unit & grounded the meter. Got a pretty steady 26.9 ohms each time. If the gas tank has about an eighth of a tank of gas in it then the 26 ohms would be about right, Right?

So why doesn't my gas gauge work?

[Greg Reid]

26.9 would probably be closer to a third or a quarter of a tank. Regardless of that, You've proven that the gauge is working and if you did it back near the tank...and it sounds like you did...it's either the sending unit or a bad connection right at the sending unit.
Sounds like you need to drop the tank and do the same check right up to the terminals on the sending unit. If your gauge still works, it's the sending unit in the tank.
Look back at the post where Jay found the problem with the connector on his unit. You may have a similar problem

["QUICK-SILVER"]

This one may actually be a worn out sending unit. The float arm moves the point contact up and down a wire wound resistor to get different ohm readings. If the resistor has a break in it, the guage will only read from the break to zero. Anything above the break would go past full.
So if the break was at 1/4 tank range (22.5 Ohms) the guage would work from there to empty and anything above that level is off the scale.

I'm afraid you're going to have to pull the sending unit out for further testing/inspection.

Could be a bad connection through the mounting plate. What pretty much put the final touches on this fuel guage thread.


EDIT
What Greg said while I was typing sloooow

[lazlo]

Yeah, I knew that but was hoping for a miracle. The sending unit on my 66 is on the front of the tank and accessible without dropping the tank. I've done a 71 gto before & it's just a pain in the arse. I don't have a lift.

I'll get started on it tomorrow.

Next question is who can you buy a sending unit from that works. As previously stated, the two new ones I got from Summit for my 66 were junk.

[Greg Reid]

The last two I bought both worked but who knows for how long...? Anyway, one was a Spectra I got at Advance Auto and the other was from Tamraz/eBay. As I say, they are both working for now but the Tamraz really looked exactly like the original '66 unit I was taking out. Not sure of manufacturer but probably Taiwan.
I'd still check the original before ordering a new one. Might be something obvious when you get to it. I hear these new ones often don't last but a couple of years. Original might last you another 40.

[lazlo]

Pulled the fuel tank today. (Found a build sheet.) Anyway I took the fuel sending unit , which was not working properly. Once out and on the bench it tested fine. Hooked it to the car & had the wife watch the gas gauge while I moved the float up & down. Everything worked like it was supposed to.

Not sure what the problem was.. Guess we'll put it back together now & see what happens..

here's a video of the bench test if anyone is interested:

http://www.youtube.com/watch?v=Y7C0o...ature=youtu.be

[Greg Reid]

Looks good to me. Do yourself a favor since you have a Volt Ohm meter. Ohm the wires out and shake them around real good, tug on the terminals and so forth. Once you R&R that tank you don't want to have to do it again. Since the unit itself seems good, there's a decent chance that you have some corrosion, a nick, or something in the wires.

[lazlo]

Originally Posted by geiser

I have been doing quite a bit of reading and have a simple question. Does the center trunk body plug line up with the sending unit?

I put in a new sending unit and tank early in my rebuild process (before the dash was in.) I found the harness was not connected on either end in the trunk after the dash was put in. I currently have a full tank. I really don't want to drop the tank to connect the harness and was hoping to pry the body plug open to connect/fish the harness to it.

Two hoses in the filler neck, at least one down in the fuel. Seal the two hose with a rag to make air tight as possible. Set a couple of 5 gallon buckets on the floor to catch the gas. Stick an air hose in one of the two hose, give it air and watch the gas come out the other hose. This very effectively causes a siphon that will empty your tank, without the nasty aftertaste...

[AdamIsAdam]

Good thread. Took several reads for me to fully understand. now I'm armed and dangerous... ready to go back to the garage and diagnose my problem. I suspect I have a bad ground.

Brief background: I just bought the car from a friend who restored it 2 years ago, including R&R tank and sending unit. He said for 2 years, the gas gauge worked fine. i get the car with what we both thought was a full tank of gas (he hasn't really driven it all winter). Well, on my first evening of driving around (with the kids no less) the car dies on the side of a dark road. it being new to me, I'm pissed and, well, pissed. Long story short, I have a buddy bring gas as I await the flatbed. Yup, it fired right up. Drove to a gas station where it took 18 gallons (after adding 2 from the gas can).

So, if the ground recently went, I'd assume it could be the corroded ground wire at the sending unit. I looked at it briefly yesterday. The connection at the sending unit (the ground wire) is nearly impossible to move. It looks ok, but it's fused solid. I guess that's my corrosion point.

I'll test by grounding the lead wire first (which comes on/off nicely) and make sure the gauge goes to E. Then I'll check the ground wire at the floorboard (which was repainted, so maybe there's not a good ground there). Then, I'll try and remove that ground wire at the sending unit. I'm just very worried I'll break the tab off in the process!

Suggestions welcome on that one.

[lazlo]

On my OEM unit the ground wire is soldered to the sending unit and will not come off. Don't tug on it to hard until you confirm it isn't soldered.