Faulty fuel senders

[Drakeule]

Does anybody have problems with the new fuel senders reading incorrectly? I checked mine before I installed it (approx. 2 ohms at empty; 40 ohms at full.) However, I know I have plus 7 gals,

in my tank, and I registers just above empty. 

Also, are all sourced senders the same (Bob's vs Old Buick parts, etc., i.e., Chinese junk)? 

[Jim Nelson]

When I restored my 35-58 fuel tank. I first measured it so it would show empty physically.      I removed it twice ( on the bench with long wires to dash gage)  bent the wire that mounted the float to make sure it would read empty when it just touched  the tank bottom.    Then mounted the fuel tank and checked it again.    BTW,  I added a ground wire from the sender all the way to the gage on the dash.    The only point that needs to be accurate is when you read empty - your empty !     If your good,  you will set the float to read empty when you have about a gallon remaining when your gage reads empty.     The rest 'is nice'  but I always keep track of fuel used,  miles traveled/  refill quantity so I know how much I use   ie. mpg.    I will NOT RUN OUT OF GAS on the road.    Personally,  I always had about 3 gallons remaining when I would refill my tank.    

[Jim Nelson]

Personally,  if its Chinese,  I won't use it.   Mexican , Taiwan etc is better quality than chinese 'stuff.    I'll pay more for good quality parts - period...   I don't want to fix something twice because I bought less expensive rather than good stuff once.  

[Bloo]

There is absolutely no room for error when setting one of these up. I marvel at the fact that GM kept this design for so long. I have been informed by another member who was there that it was not a problem in production, and I believe him, but I still marvel at it. New senders are universal fit for a bunch of different Buick tanks, made by some third party, shipped in from wherever and possibly clobbered by modern shipping methods. In my opinion, there is not a snowball's chance in hell of one of them working right if you just install it and hook it up. That is true no matter who made it or what country they made it in. An original part (my preference) also needs careful scrutiny after being rebuilt.

 

To start, disconnect the wire from the tank. With the key on, the gauge should peg past full. Now ground the wire at the tank. The gauge should go to empty. If it won't do this, there is trouble with the gauge, the gauge ground, the tank ground, or the wiring that must be addressed.

 

2 hours ago, Drakeule said:

I checked mine before I installed it (approx. 2 ohms at empty; 40 ohms at full.)

Buick gas gauges up until 1964(?) or so are 0-30 ohms. Did you zero your meter? You'll never get to E with 2 ohms. If you have a meter that you cannot zero, touch the leads together, note the number you see. It is the resistance of the test leads. Subtract it from the reading you get on the sender. If the sender can go to 40 ohms in tank, there will be a bunch of gas at the top of the tank that gets used with the gauge pegged full before the gauge needle even starts moving down.

 

2 hours ago, Drakeule said:

However, I know I have plus 7 gals,

in my tank, and I registers just above empty. 

Starting with a completely empty tank, off of the car and drained, and a correctly working sending unit, there is going to be some gas that cannot be reached by the pickup and is simply lost. Then there is the reserve, possibly 1.5-2 gallons, that lives in-between the gas that can never be retrieved and the point where the gauge starts moving up. I don't think all that explains 7 gallons, but it explains part of it.

 

The pickup should be as low as possible. In my opinion there should be a sock filter on it. Verify the sock does not interfere with the float. The float should get very low in the tank and should be very close to 0 ohms (less than an ohm) at the lower stop. This should not change with the sender in or out of the tank, because the float should never hit the bottom of the tank, but almost! If you flip the tank upside down, the sender should hit the stop before the float hits the top of the tank. The float should almost hit the top of the tank, but not quite. The resistance should be 30-ish ohms. There must be 30 ohms difference between E and F to get full swing of the gauge. A bunch of extra ohms at the top will result in a bunch of gas needing to be used before the gauge starts to go down.

 

The arm length on a universal sender may be wrong. Too long, and it may hit the top of the tank before reaching 30 ohms. Too short, and it may get to 30 ohms too soon. Correct if necessary. Make sure the float isn't going to hit anywhere.

 

Once you have 0 ohms empty with the tank right side up and 30-32-ish with the tank upside down, you can check the reserve if you want. put enough gas in to make the resistance come up above 0 ohms slightly. Using a HAND POWERED (definitely not electric) transfer pump, suck gas out of the tank through the fuel pickup. Keep jiggling the tank, as some sending units have a brake on the arm. When the meter is back to 0 ohms, put the output hose of your pump in a different container. Pump until you can no longer get gas from the tank. The gas in the second container represents the size of your reserve. Slightly bending the float arm can change the reserve if it is not reasonable.

 

Always add a ground strap or wire from a sender screw to the body or frame of the car. This prevents calibration changes as the gas tank's grounding to the rest of the car deteriorates over time.

 

 

Edited June 15, 2022 by Bloo (see edit history)

[Rock10]

That is very good info.

[Century Eight]

So Drakeule, have you figured out if all these popular suppliers you mentioned, source their sending units from the same place?  Nobody really answered that yet.  I’ve  done this job on my fifty a few years ago and I am very familiar with all the comments and pitfalls.  However this time, on my forty, it was in a shop for a bunch of other things so I had them drop the tank and put in a new sending unit that they got from Old Buick Parts (CARS).  When I got it back in March, it sort of worked on the way home, but a bit bouncey.  After sitting for two months, when I started it again, with a known seven gallons in the tank, it now pretty much sits on empty but sort of flutters when i do hard stops and moves a little when on a hill.  That makes me think the gauge (recently professionally rebuilt) is okay and the electrical connections are working.  So when it’s back for more work next month, the guy is going to first check it out with the ohmmeter.  I suspect the sending unit is crap and from the other side of the world, but I didn’t see it.  

 

I’d be interested to know if you have found a good source for working units in your search yet.  The one I got three years ago works fine in my fifty but maybe they are a lot worse now.  

 

Phil

Edited June 16, 2022 by Century Eight (see edit history)

[Ben Bruce aka First Born]

Phi, I suspect there is a loose or corroded connection somewhere.  I will bet dollar to a donut they did not ground it properly. Original is connected directly to the gas line.  Replacement is connected to the line with a rubber hose, therefore no ground. Is yours accessible without dropping the tank?

 

  Ben

[Century Eight]

So Drakeule, have you figured out if all these popular suppliers you mentioned, source their sending units from the same place?  Nobody really answered that yet.  I’ve  done this job on my fifty a few years ago and I am very familiar with all the comments and pitfalls.  However this time, on my forty, it was in a shop for a bunch of other things so I had them drop the tank and put in a new sending unit that they got from Old Buick Parts (CARS).  When I got it back in March, it sort of worked on the way home, but a bit bouncey.  After sitting for two months, when I started it again, with a known seven gallons in the tank, it now pretty much sits on empty but sort of flutters when i do hard stops and moves a little when on a hill.  That makes me think the gauge (recently professionally rebuilt) is okay and the electrical connections are working.  So when it’s back for more work next month, the guy is going to first check it out with the ohmmeter.  I suspect the sending unit is crap and from the other side of the world, but I didn’t see it.  

 

I’d be interested to know if you have found a good source for working units in your search yet.  The one I got three years ago works fine in my fifty but maybe they are a lot worse now.  

 

Phi

[Century Eight]

Ben, he actually added an additional ground from the tank to the frame.  But I will recheck the connections.  There is no access on this car unless you drop the tank.

 

Phil

[Bloo]

Low reading is probably a sunk float. Disconnecting the wire should make the gauge peg high. Ground troubles at the tank should also make the gauge read high not low.

 

Bounciness might be unavoidable because the AC (GM) gauge is an instant response type. In the mid 30s, the senders had a brake made of cork to counteract it, but the brake might not work after all these years unless someone rebuilt it. When they are working right, the senders don't really respond until bumps and road vibration are encountered. These are the sending units that have 2 exposed gears. I think Buick may have stopped using them by 1940(?). The newer Buick type does not appear to have a brake, but I am not 100% sure of that. A modern replacement sender definitely wouldn't have one.

 

I don't know if the Bob's and the C.A.R.S. sending units are the same or not.

 

[Century Eight]

We’ll figure it out in a couple weeks.  When i got a new unit a few years ago for my fifty, the float was bad off the shelf so we put another float in and then the sending unit worked fine.  We may end up doing the same for this forty.  Too bad to pay for junk.

Edited June 16, 2022 by Century Eight (see edit history)

[Drakeule]

All:

 

I decided after fiddling with the off shore unit, to scrap it and put the original cleaned up sender back in. I have just replaced the corks and used hot fuel dope (available from model air crafter places) to coat them; I did this with a two stroke boat engine float that I replaced a while back-worked fine.

 

A work in progress; I'll tune in after I get the tank back in.

[Gary W]

I had to "recalibrate" my sender.  I did have it restored, but at empty it wouldn't drop to "0" Ohms.  After a little grinding and bending the float arm, I finally got it as close to zero as I could without ruining the gear mechanism.  There are some diagnostics you can run with the tank out before you reinstall to get it reading more accurately.  Good Luck!

 

Here's my post(s) on my sender repair:  Just hit the upper right arrow:

 

 

[Drakeule]

Gary W; thanks for that input. I remember your discussion now; running out of gas close to home is not easy on the Ego, Ask me how I know...

 

Well, I cleaned up the old sender, reinstalled it, and put exactly 4 1/4 gallons in the tank; this should have shown 1/4 full. It actually showed a skosh under that. I then drove to the gas station and put another 4.5 gals in the tank; it was dead on 1/2. full. So that's it; no more dropping the tank (however, never say never....)

 

The new one is just bad, so I'm sending it back to Bob and let him look at it.

 

Now, I have the exact same off shore sender in my Super, and it works fine. I guess the answer is probably poor quality control.

 

Thanks again all.

 

CD