Ok after rebuild and the 100s of hours (sometimes after 2 and 3 in the morning) all I wanted to do was drive it. Now however, a nagging problem that I have ignored needs attention.
The fuel gauge will read a quarter fule when the car will run out of gas. After filling up the gague will read 1/2 full. Any suggestions. This is a new tank and sending unit but its anoying.

Is your temp gauge out of whack, too?

Assuming that the Constant Voltage Unit (mounted on the rear of the instrument cluster) is OK (that's why Joe asked if the Temp gage is out of whack), the culprit is more than likely the Fuel Tank Sending Unit. The first check I would do is (with the ign key in the ON or ACC position) remove the wire from the sending unit and ground it to the chassis. The fuel gage should read FULL. If it doesn't go to the FULL position, the gage or wire to it is at fault.
If the fuel gage does go to the FULL position with the sender wire grounded, then the tank sending unit is at fault.
Let me know how this test works, and we'll go to the next step.
Neil Hoppe

Here's a quick check to tell if the tank sender is OK. Disconnect the wire at the sender. Put one lead of an ohmmeter on the sender stud and the other lead on a GOOD chassis ground. If the tank is full of gas it should read about 15 ohms. If the tank is empty, it should read about 75 ohms. If you think the tank is about half full it would be 45 ohms. I'm giving you these numbers from memory but I'm pretty sure that's what it should be. To see if the wiring is OK, pull the instrument cluster out far enough to access the wiring on the back. Disconnect the wire to the tank (the negative side of the gauge) and measure from it to ground. With the wire back on the sender, you should get the same reading you got at the sender. If this is all good, you need a new gauge or constant voltage unit. I have the same problem with mine but the gauge only goes to half full with a full tank and drops to empty with half a tank. I'll be getting the solid state volt. reg. on my next parts order to see if that solves the problem, otherwise it's time to rebuild the gauge.

Steve

My car has the same problem except it goes frm 1/2 to 3/4. On one of my trips I hit a huge bump while the guage read 1/2 and it swung nearly to empty. That tells me that the new sending unit is too stiff and is sticking.

If you discover the problem is the sending unit I think you'll find that it seems to move freely if you move it with your hands but not quite freely enough for it to overcome the force supplied by the float.

Does anyone know how to lighten the force between the contact and the coils? Can we just bend the contact, or file it?

Is your temp gauge out of whack, too?

Hey all,

I think I have this same issue.

My fuel gauge shows 3/4 when it's a full tank...and my temp gauge never goes above 1/4 (usually an 1/8th of the way between C and H)

I guess my question to Joe is- Is out of whack more on the cold side? Or more on the hot side? Or all over the board?

Thanks,

Jeff

PS- Does all of this have anything to do with my in dash clock working only sometimes ;-)

Thanks - its raining here like crazy - the temp gauge and all work fine except for the fuel. I will try the wire in the a.m. You know what a pain it is to drain and pull the sending unit. Must be sticking. I'll dial in and let you know thanks!!!

Hey all,

I think I have this same issue.

My fuel gauge shows 3/4 when it's a full tank...and my temp gauge never goes above 1/4 (usually an 1/8th of the way between C and H)

I guess my question to Joe is- Is out of whack more on the cold side? Or more on the hot side? Or all over the board?

Thanks,

Jeff

PS- Does all of this have anything to do with my in dash clock working only sometimes ;-)

You need to change out your instrument voltage regulator. Make sure you disconnect your battery when you do this because it's kind of a PIA and it doesn't take much to short out the regulator.

All,
If the gauge goes to full tank when grounded, this is something else I experienced.

Some of the fuel sending units I have received work just fine, but are not “adjusted” properly to the tank. They are to far above the floor of the tank and when full do not register full because they are only moved half way through the range of measurement.

My brothers 64 Comet Caliente did this. With an empty tank with it still in the car, I was able to bend the arm to get the float to rest on or near the tank floor when in the empty position. In fact we played around to get it to show empty with 2 gallons in the tank so his son would not run out of gas. “Son, when it says empty you best be near a gas station!!”

Hopefully you have a drain plug or just bring it home empty. BE VERY CAREFULL around any gas sending unit. Us a brass punch to spin the ring. No sparks around the tank. Especially an empty tank. They are the easiest to light off. Old tanks have the most gas imbedded in the metal. A new tank can be blown out fairly well with an air compressor with the sending unit out and the gas cap opened. Just carefully blow some air through it. If you have an assistant, you can keep a gentle breeze through the tank when you work. I was a radiator repairman a few hundred years ago and also fixed leaky tanks. Always was a rush to put flame on a gas tank!!!!

Rob

You need to change out your instrument voltage regulator. Make sure you disconnect your battery when you do this because it's kind of a PIA and it doesn't take much to short out the regulator.

A little off subject, should one (that would be me) replace the instrument voltage regulator if he's renewing the wiring system and the instrument cluster is out of the car?
I don't know if it's good or bad condition.

While it is opened up, an excellent time to replace the V/R. You can now get a solid state unit- well worth the price.
Neil Hoppe

Thanks Guys!
I know it been 6 monhs but last weekend I pulled the sending unit out of the convertible and compared it to the CS original. BIG difference. Another one of those aftermarket parts being touted as NOS - NOT! Its the one with the yellow wire wraped around the tube. I had to bend the heck out of it to match the original. Put it back in - and it worked great - except the float needs to be bent a little more (stays below the E w/ 3 gal. and does not go past the F when full. Going to pull it again when empty. Then I'll be ready for that 6 hour road trip to Houston.

I've been super busy lately, but today decided I needed some "me and my CS" time. It's up on jack stands so I decided to look at this gas gauge thing again. I grounded out the wire to the unit and the gauge went way past full, so I decided I'd look at the sender, drained the tank and took it out. I noticed the float was held to a stud for the reostat with a small screw so loosened the screw (I think it's locktighted in place) and tweaked the setting until I had 5 ohms of resistance at "full" instead of the 15 I had before. The "empty" reading became 65 ohms instead of 75. I put the sender back in and checked the gauge. When I turned the key on, the gauge moved from the past "E" resting spot to exactly "E". I haven't filled the tank yet but think I might be on to something. I have 3 feet of snow in the yard so will have to fill the tank 2 gallons at a time, so I'll be able to see if 4 gallons gets me to 1/4 tank, etc. I'll let everyone know what I find.

Steve

Holmes,
Yes, another fuel sending unit that need to be bent and calibrated to the tank it was in. I check this every time I put a new one in. Got to where I could get them to read empty on the gauge with two gallons left.

I have the "low fuel" sending unit in mine. Anyone seen a repop for it or maybe Neil or Steve rebuilds them??

Rob

Yes, that is a common XR7 Cougar part. :grin:

http://www.cougarpartscatalog.com/elfi.html

Well, how cool is that!!!! For the anal guy that hates it when all the stuff doesn't work......

That might be me....

Thanks!!!!

Rob

Here's an update. As time permits, I've been draining the tank, adjusting the sender, refilling (4 gallons at least) and checking. I now have the sender adjusted down as far as it will go---to .7 ohms in the full position and 50 ohms in the empty position. With no gas in the tank, it will read "E". With 2 gallons it will just come off of "E" and with 4 gallons it will be a needle's width above 1/8 tank. It appears the reostat in the sender isn't linear so this is the best I can get with the current sender. It's a whole lot better than it was before though and I know when I'm at 1/8th tank I better be looking for gas soon. I apologize for assuming my new sender was set correctly before and giving erroneous numbers. The lesson is, measure your new sender with an ohmmeter before installing. Loosen the lock screw and adjust if necessary. I hope this helps out my fellow CS'ers.

Steve

You might want to make sure the sender is properly grounded. If you painted the tank, reused old rusty screws, the sender can not ground. You can attach a wire directly to a good ground and then touch the other end to the sender to test it.

You might want to make sure the sender is properly grounded. If you painted the tank, reused old rusty screws, the sender can not ground. You can attach a wire directly to a good ground and then touch the other end to the sender to test it.

Thank you. I'm fairly confident the ground is good. :wink:

Steve

Steve has been to this rodeo many times.... What does DC mean?? Damn Corn-fusing!! When you have a problem with electrical stuff on a car...... "Its always a ground"!!!

And why do the British like warm beer??? "They all have Lucas refridgerators"!!!!

Sorry, I had to say it again....

Rob

Steve has been to this rodeo many times.... What does DC mean?? Damn Corn-fusing!! When you have a problem with electrical stuff on a car...... "Its always a ground"!!!

And why do the British like warm beer??? "They all have Lucas refrigerators"!!!!

Sorry, I had to say it again....

Rob

Lucas is also referred to as 'The Prince of Darkness'. :cheesy:

Hi

Has anyone converted a standard 5/16 mustang fuel sender unit to a 1/2 inch fitting ???

shaun