Moparts
Fuel sending units reading WRONG....time after time
Posted By: shadango
Fuel sending units reading WRONG....time after time - 03/13/10 09:16 PM
Hey guys. Hoping someone may have some insight into this issue.
72 Barracuda. From what I can tell, stock tank. It had what appeared to be a stock sending unit in it when I got the car, and it was toast.
I bought a new one from Rock Auto....got it and found it didnt read right. Like it would read 1/2 tank when the tank was full. bent the float arm and after numerous trials and errors got it to read right at half and full. But found it had numerous dead spots....the gauge would go to empty for a few miles and then go back to the correct level.
Well, thinking it was a cheap sender I sent it back and bought a "better" one from a well knowm Mopar restoration outlet. The unit had a larger price, about $50 more as I recall....the unit LOOKS to be better quality for sure. Ok, so installed that and found that it read a half tank when the tank was full.
Many more trials and errors , which includes draining the tank to half so I can pull the sender , and I once again have it reading properly at half and full. But this time I find I still have two dead spots...one at half and one at 1/4 tank. I confirmed that it was the sender by running several tanks of fuel through it. Every time, same spots, same results...drops to empty. A few miles later and it goes back up. At least it was predictable.
I brought this to the attention of the vendor and he suggested I return it sinice it wasnt right.
Well, I have the new one in and once again, I have a half tank of fuel in it (8.25 gallons) and the gauge reads just barely off of empty.
Before I go thru yet another round of drains/bending/refills, does anyone have any ideas here?
I have checked the sender out of the tank, hooked up to the wiring/gauge.....when the float is all the way down the gauge (stock dash) read empty.....all the way up, it reads full. Just like it should.
The tank appears to be stock and it does hold just about 16.5 gallons or so.
The ground strap is new....and connected good. I even ran a second ground wire and ran it straight to the battery to see if that would change things....no change at all.
I for the life of me cant understand why I am having this weird issue.
It seems like the sender is the wrong one or something for the tank.
But I have looked and the same sender unit is specified for all years of e body cars.
Anyone? I am at wit's end!
Posted By: RapidRobert
Re: Fuel sending units reading WRONG....time after time - 03/13/10 09:36 PM
I would check the ohms with it still installed in the tank as is, at the 2 dead spots which would confirm an open in the sending unit windings. I'm wondering if when you mock it up & manually move it thru it's travel that you are holding a bit of side pressure onto the arm as you move it across the windings whereas in the tank it is more free floating and hitting 2 places in the windings that are not flat & hence no contact. but for 2 senders to be acting the same (if I read that right), I agree that does not have a logical explanation but it's gotta be something simple (after we find it) and I wanted to throw something out there to (hopefully)contribute.
Posted By: bboogieart
Re: Fuel sending units reading WRONG....time after time - 03/13/10 09:40 PM
Being as it has happened with three different senders, might it be else where? The gauge maybe?
Just a suggestion.
Posted By: BergmanAutoCraft
Re: Fuel sending units reading WRONG....time after time - 03/13/10 09:58 PM
Just as an FYI to add to this issue, I have a B body tank that was stamped wrong, and the angle of the sender is such that the sweep isn't from the bottom to the top of the tank. Very strange. You wouldn't know it, unless you put an angle gauge on the tank...
Have you checked the ground?
Posted By: 70duster340
Re: Fuel sending units reading WRONG....time after time - 03/13/10 10:24 PM
I would make sure that all your grounds are connected (engine to frame, frame to body, body to engine). My stock sending unit only worked part of the time, and after it was at a shop and they claimed it was working and it was not, I checked and repaired/replaced all the grounds, and now it works correctly.
Posted By: Y3 70 BEE
Re: Fuel sending units reading WRONG....time after time - 03/13/10 11:15 PM
Last year I did a little test that included putting in a original factory sending unit to replace a repro which I think is a spectra. Before doing this I ohm tested both units per the factory book and both read within specs well the factory unit read correct when put in the tank and the repro did not. I put the repro back in because I run 3/8 and the factory one I had was 5/16 so until I know of a accurate repro or get a original unit in 3/8 I will live with it I have not tried the bending the arm method yet.
Posted By: BDW
Re: Fuel sending units reading WRONG....time after time - 03/14/10 12:06 AM
Quote:
I would check the ohms with it still installed in the tank as is, at the 2 dead spots which would confirm an open in the sending unit windings. I'm wondering if when you mock it up & manually move it thru it's travel that you are holding a bit of side pressure onto the arm as you move it across the windings whereas in the tank it is more free floating and hitting 2 places in the windings that are not flat & hence no contact. but for 2 senders to be acting the same (if I read that right), I agree that does not have a logical explanation but it's gotta be something simple (after we find it) and I wanted to throw something out there to (hopefully)contribute.
Take the sender out and measure the resistance as you move the arm. If this works then it has to be somehwere else. Grounds are the next logical problem spot. If all else fails replace the instrument voltage regulator.
Posted By: moparmikethree
Re: Fuel sending units reading WRONG....time after time - 03/14/10 12:34 AM
If the sending unit is a one wire unit, there must be a ground strap that goes from the sending unit outlet and connects to the main fuel line.
Jumps over the rubber hose, needed to have a good ground
Posted By: Pool Fixer
Re: Fuel sending units reading WRONG....time after time - 03/14/10 12:35 AM
three senders all wrong? I'd yank that gauge, clean the contacts, check your cluster ground, find an ohm chart, then buy resistors from radio shack and use them to adjust the gauge.
Posted By: 1_WILD_RT
Re: Fuel sending units reading WRONG....time after time - 03/14/10 01:10 AM
Quote:
three senders all wrong? I'd yank that gauge, clean the contacts, check your cluster ground, find an ohm chart, then buy resistors from radio shack and use them to adjust the gauge.
Sorry I've sorted out enough gauges on these cars to tell you the repo senders are junk... To test the gauge IVR & wiring a gauge system tester is the tool of choice..
But the fact he has plugged in an original sending unit & it works tells me the repo senders have all been bad...
Personally I've had the last three fuel senders rewound by my local instrument repair shop.. Costs more than a repo sender but it works...
BTW They can rewind the 3/8 repo sender too...
Posted By: Y3 70 BEE
Re: Fuel sending units reading WRONG....time after time - 03/14/10 01:34 AM
I was thinking of removing the sending unit part of the original pick up and using it on the repro. Have to look about doing some surgery.
Posted By: bboogieart
Re: Fuel sending units reading WRONG....time after time - 03/14/10 01:40 AM
But the fact he has plugged in an original sending unit & it works tells me the repo senders have all been bad...
If this were the case he would not have a problem would he? He would have a sender that works right?
He does not, time to look else where. He said that all his grounds are good time to look else where.that leaves wiring and the guage doesn't it?
Posted By: Pool Fixer
Re: Fuel sending units reading WRONG....time after time - 03/14/10 01:41 AM
Quote:
Quote:
three senders all wrong? I'd yank that gauge, clean the contacts, check your cluster ground, find an ohm chart, then buy resistors from radio shack and use them to adjust the gauge.
Sorry I've sorted out enough gauges on these cars to tell you the repo senders are junk... To test the gauge IVR & wiring a gauge system tester is the tool of choice..
But the fact he has plugged in an original sending unit & it works tells me the repo senders have all been bad...
Personally I've had the last three fuel senders rewound by my local instrument repair shop.. Costs more than a repo sender but it works...
BTW They can rewind the 3/8 repo sender too...
still can't hurt to check the grounds and test the gauge. I did 3 of them a couple of years ago. 2 were pretty good...one was way way off. Even if it's the sender, still a good idea to get the ohm chart and check the gauge.
If you intend on opening up a resto shop or selling restored clusters, that tester (what is it called, a decade resistance something?, I forget) is great. For the backyard guy fixing his fuel gauge, 5 bucks worth of junk from radio shack will do the job just fine.
The gauge is more than 35 years old, it couldn't hurt to check it
Posted By: bboogieart
Re: Fuel sending units reading WRONG....time after time - 03/14/10 01:46 AM
Yep I could be wrong happened once before I thought I made a mistake but I was wrong.
I agree time to look into the rest of the system.
Posted By: 1_WILD_RT
Re: Fuel sending units reading WRONG....time after time - 03/14/10 01:53 AM
Quote:
But the fact he has plugged in an original sending unit & it works tells me the repo senders have all been bad...
If this were the case he would not have a problem would he? He would have a sender that works right?
He does not, time to look else where. He said that all his grounds are good time to look else where.that leaves wiring and the guage doesn't it?
I incorrectly thought the original poster & Y3 70 Bee who posted "I ohm tested both units per the factory book and both read within specs well the factory unit read correct when put in the tank and the repro did not. I put the repro back in because I run 3/8 and the factory one I had was 5/16 so until I know of a accurate repro or get a original unit in 3/8 I will live with it" were the same person...
And yes checking grounds is obviously a good idea & I always break out my gauge tester before replacing the sender.. But bad repo senders are way more common than you want to believe..
Posted By: shadango
Re: Fuel sending units reading WRONG....time after time - 03/14/10 05:24 AM
Just to reiterate what I did:
I tested thecurrent 'better" repop I have as well as the last one outside the tank....hooked up the wire and the ground and tested that way.....the gauge registered full when I raised the arm to full, and measured empty when at rest at the empty end of the swing.
It just seems like the unit itself is calibrated wrong for the tank.....the dead spots are a seperate issue, as once I tweaked the first couple units for the level it seemed ok aside from the dead spots.
In my case the original sender didnt work at all...I did compare it to the first (cheaper) repop and tyhey looked basically the same aside from the repop seeming "cheaper". I have since tossed the original (dumb move). The "better" repop appears to be the same as the cheaper one in terms of measurements.
I am convinced that the gauge itself and ground are fine.
Posted By: BDW
Re: Fuel sending units reading WRONG....time after time - 03/14/10 01:30 PM
Sounds like your only issue now is the dead-spots?
If that's the case, take both senders out and measure the resistance as you move the arm. The resistance should increase/decrease at a fairly constant rate. As was stated, you'll probably seen a "jump" at a certain point in the travel. Look closely to see if there are any irregularities in the windings/arm at this point.
Maybe your adjustment/bending the arm caused intermittent contact at certain points during its travel.
Posted By: dobie
Re: Fuel sending units reading WRONG....time after time - 03/14/10 04:07 PM
I can't offer anything of help, but I can say that I'm experiencing the same thing. The first sending unit was way off, so I put another one in. This one too is way off. A full tank of gas reads 1/2 on the gauge. I took that one out and tried bending the float arm. Of course it's still way off. Once the body work gets going this summer I'll pull the tank out and go over it one more time. After that, I'll just deal with it I guess. Not that I go on many long distance road trips anyways I suppose.
Posted By: shadango
Re: Fuel sending units reading WRONG....time after time - 03/15/10 01:54 AM
I spent some time today once again bending the arm of the latest sender to reflect a half tank of gas.
What a pain.
At least I knew more or less how I needed to bend it this time....
I wont know if I have dead spots for sure until I actually run a full tank now. And I wont know if the full reading is OK or not (before, my bending resulted in a full reading waaay past the usual full mark).
I have tried the ohm;s test/sweeping the arm......I think I mentioned that in the first post.....the last one I detected no dead spots but had them anyways.
it could be that my tweaking induced them as was suggested.
That said, my main concern is why these senders are so off....I mean, showing a empty tank when its half full seems to indicate an issue...after searching a bit, I have found that its (thankfully) not just me.
Some folks seem to have great luck with the senders working the first time....then others have the same issue I am....
So, what is the difference?
All I can figure is there is some difference in the tank itself....maybe the dimensions are off?
Dobie, maybe we can compare notes....what year/model car are you working on?
I dont have any cross country trips planned, but I do have a couple of 300 or so mile trips planned and knowing how much gas you have is always a good thing, even on short cruises...LOL
At least I know that at half tank I have a half tank left....LOL
Posted By: RapidRobert
Re: Fuel sending units reading WRONG....time after time - 03/15/10 02:14 AM
I didn't realize that they were that problematic. makes me want to get a new stock one & if it reads right then add the 3/8 line myself. Only difficult part would be to swedge the flat to get some more contact area to keep the line in place or some sleeve/nuts to anchor it. What are the stock ohms supposed to be? Was it 10 and 70
Posted By: ahy
Re: Fuel sending units reading WRONG....time after time - 03/15/10 03:09 AM
I've used 2 repops from 2 companies. Both showed "E" at half tank. Both failed the FSM ohm vs position test. Wish I hadn't pitched my old 5/16" pickup. I would have made the effort to mod it to 1/2".
Posted By: Sixpak
Re: Fuel sending units reading WRONG....time after time - 03/15/10 06:38 PM
My experience with an aftermarket sending unit was pretty bad, too. Take a GOOD look at the quality of the windings on the rheostat on the old and new unit - you'll see a big difference. Those Spectre units are JUNK - the wraps should be tight next to each other, with no spaces between the windings. That's where part of the problem is. Also, the fewer the number of windings, the less overall resistance the gauge will see, throwing off the readings there as well. I ended up using my old sending unit and using the plastic float from the new unit, but still had to bend the float arm a bit to get the old unit to read sort of correct with the new float.
Posted By: Sixpak
Re: Fuel sending units reading WRONG....time after time - 03/15/10 06:40 PM
Quote:
I didn't realize that they were that problematic. makes me want to get a new stock one & if it reads right then add the 3/8 line myself. Only difficult part would be to swege the flat to get some more contact area to keep the line in place or some sleeve/nuts to anchor it. What are the stock ohms supposed to be? Was it 10 and 70
If you do try to modify a stock one be sure to remove ALL the electrical components off the thing before try to solder a larger fuel pickup tube to the plate...DAMHIK...
Posted By: RapidRobert
Re: Fuel sending units reading WRONG....time after time - 03/15/10 07:09 PM
Quote:
If you do try to modify a stock one be sure to remove ALL the electrical components off the thing before try to solder a larger fuel pickup tube to the plate...DAMHIK...
Sixpack I will follow your advise. Any idea what the ohms are supposed to be?
Posted By: Sinitro
Re: Fuel sending units reading WRONG....time after time - 03/15/10 08:27 PM
The sending unit is a rheostadt just like a volume control.. The resistance varies which changes the voltage sent to the guage. If you have open readings then the circuit is open during those times pointing to an intermittant rheostadt winding.
EZ to check...
With the sending unit out of the tank and grounding wire connected. Have a buddy read the guage as you vary the sending unit. Action should be smooth and consistent, if not then the sending unit is likely damaged..
Just my $0.01...
Posted By: shadango
Re: Fuel sending units reading WRONG....time after time - 03/16/10 09:39 AM
In my experience with the last 3 senders, that test works, but its not 1005 accurate.
The sensitivity of the rheostat inside is very high. If you have shaky hands at all you will get error.
True, if you see a large swing in ohms there is an issue....but smaller swings or smaller dead spots may not be visible until it is installed and being affected by the actual fuel level.
In the cheap Spectra one from Rock auto, I found the dead spots by hand easily. On the better units from Roseville, not so easy....seems that the dead spots were much smaller...but still there.
We'll see what this one does I guess.
I am not expecting much to be honest. At this point I would settle for predictability at least....on the last sender I knew there was a short dead spot at half and 1/4 tank....un-nerving to look down and see "empty' but after a few tanks it was at least predictable.
I also keep a log of my mileage so as to know how many miles into a tank I am "just in case". Of course my speedo occasionally goes berserk, above 60 mph.....and affects the odometer....but that is a whole other thread...and one of the projects on my list....
Posted By: Sixpak
Re: Fuel sending units reading WRONG....time after time - 03/16/10 11:22 AM
Quote:
Quote:
If you do try to modify a stock one be sure to remove ALL the electrical components off the thing before try to solder a larger fuel pickup tube to the plate...DAMHIK...
Sixpack I will follow your advise. Any idea what the ohms are supposed to be?
Sorry, no...I just remember ruining the electrical components on mine when I tried to solder a 1/2" pickup into mine. I got to believe they swedge or solder the tube to the plate first and then add the electrical stuff. Those things aren't really built to be disassembled so take your time.
Posted By: rapom
Re: Fuel sending units reading WRONG....time after time - 03/16/10 12:13 PM
This has been a problem on the Charger forum when changied to the new 3/8 pickup. What a lot of guys do over there is they take the old sender and attach it to the new pickup. I myself changed the guts of the sender back to the old setup. Won't know I well it works for another couple of weeks.
Posted By: GTXX
Re: Fuel sending units reading WRONG....time after time - 03/16/10 04:42 PM
Quote:
I've used 2 repops from 2 companies. Both showed "E" at half tank. Both failed the FSM ohm vs position test. Wish I hadn't pitched my old 5/16" pickup. I would have made the effort to mod it to 1/2".
many years ago I modded one by adding a second 3/8" line. drilled a hole in the pick-up, silver soldered in steel line bent the same as the original pick-up. had one line for carb, one for N2O system. worked perfect.....
Posted By: ademon
Re: Fuel sending units reading WRONG....time after time - 03/16/10 04:48 PM
We need on of the quality companys that repop parts to think about repoping a hi quality sending unit,
Posted By: 1_WILD_RT
Re: Fuel sending units reading WRONG....time after time - 03/16/10 04:52 PM
Posted By: aarcuda
Re: Fuel sending units reading WRONG....time after time - 03/16/10 05:22 PM
10ohms = full
72 ohms=empty
Posted By: RapidRobert
Re: Fuel sending units reading WRONG....time after time - 03/16/10 08:02 PM
Quote:
10ohms = full
72 ohms=empty
Thank you. I will record them
Posted By: Noblewk
Re: Fuel sending units reading WRONG....time after time - 03/17/10 12:54 AM
Check the 5v Regulator....... The old ones are crap. My Fuel and Temp used to creep up and down with no reasoning. Updated the 5V Regulator and now they are solid.
http://www.mopar1.us/instrument.html
Posted By: aarcuda
Re: Fuel sending units reading WRONG....time after time - 03/17/10 01:18 AM
Quote:
Check the 5v Regulator....... The old ones are crap. My Fuel and Temp used to creep up and down with no reasoning. Updated the 5V Regulator and now they are solid. http://www.mopar1.us/instrument.html
i made one of these using a different design. it was in a magazine as well but i dont believe the mounting tab of the LM voltage regulator was the output pin. I remember screwing the LM volltage regulator to the inside of the case of the old mechanical VR and the case acted like a heat sink. All of the components fit into the case and attached to the original leads so you can pop the unit right back into the dash and it looked stock
Im still running it 10 years later
Posted By: aarcuda
Re: Fuel sending units reading WRONG....time after time - 03/17/10 01:21 AM
Posted By: Dixie
Re: Fuel sending units reading WRONG....time after time - 03/17/10 03:02 PM
Quote:
We need on of the quality companys that repop parts to think about repoping a hi quality sending unit,
This is not directed at anyone in particular, just an industry observation.
Years ago we had some sending units made by the same vendor Chrysler used then and uses now. When the overseas repro's came out, and were cheaper, everyone started buying those. So, we quit making them. Hey, that's business.
Even today at shows, as I sell off the remaining inventory, people don't care about quality. They want cheap. I can't tell you how many times, I have told people the overseas stuff is junk, it goes in one ear and out the other. Your best bet is to have an original rebuilt like Randy stated above, or buy NOS. Of course, on a 40 year old car, wiring and gauges can all be contributing factors.
I hate to say it my Mopar brothers, but some folks just don't care about quality, and when price becomes the driving factor, it affects the parts we all have to choose from.
Posted By: shadango
Re: Fuel sending units reading WRONG....time after time - 03/18/10 02:01 AM
Well, I bought the Rock Auto $70 first because I figured "whats the diff".
After 2 of those I decided to spend more money. A full $50 more....
While it got a LITTLE better (fewer/smaller deadspots) the acuracy still sucks eggs.
I dont mind paying more for better quality.
Its when you pay more and it STILL doesnt work right that I feel ripped off.
Posted By: dobie
Re: Fuel sending units reading WRONG....time after time - 03/18/10 11:12 AM
I'm working on a '68RR. When I got the car it had the original tank in (I believe.) The sending unit never did work. Then my uncle gave me a new unit bought from Herb's Parts. That one was better, but still reading way off. Last year I developed a leak in the tank so I bought a new aftermarket tank. After putting the new(er) sending unit it, it was off. I took it back out and tried bending the float arm. That didn't work, as it still shows E on a 1/2 tank approx.
Later this year things should start coming apart for the body and paint, so I'll play with it one more time. After that, I'll give up. I've even thought about installing an aftermarket gauge near my triple gauges under the dash. We'll see I guess.
Posted By: dan9
Re: Fuel sending units reading WRONG....time after time - 03/18/10 01:05 PM
would it make any difference if instead of bending the arm try spinning the arm on the shaft near the rheostat?
Posted By: Kern Dog
Re: Fuel sending units reading WRONG....time after time - 03/18/10 04:50 PM
Every post here makes sense, especially regarding how people are inclined to buy CHEAP. I built my 70 Charger in 2003 and had a new gas tank and 3/8 sender shipped from Year One. At that time, I knew of no other fuel sender vendors other than The Paddock. I had to spend $ 160 for the sender only to find that at full tank it read 5/8. No dead spots, but it was slow to move from 5/8, then when it did, it fell FAST as if I just drilled a 2" hole into the tank. What a piece of crap. Being a Mopar guy has always seemed like we have to improvise/adapt and overcome.I don't know how many times that I have said to myself that " I MUST really love these cars to put up with this kind of stuff."
Posted By: Dixie
Re: Fuel sending units reading WRONG....time after time - 03/19/10 12:58 AM
Quote:
I don't know how many times that I have said to myself that " I MUST really love these cars to put up with this kind of stuff."
LOL, I've said the same thing several times in the last 28+ years messing with these things. Sometimes even with good parts, they can be boogers.
Posted By: RapidRobert
Re: Fuel sending units reading WRONG....time after time - 03/19/10 01:07 AM
Quote:
I don't know how many times that I have said to myself that " I MUST really love these cars to put up with this kind of stuff."
One thing this hobby has done for me is my tolerance for frustation is now very high w plenty of patience. I take a breather, and a good nights sleep then mentally/physically deal w it some more until I get it resolved
Posted By: Steve340
Re: Fuel sending units reading WRONG....time after time - 03/19/10 01:22 AM
I don't think anybody calibrates these gas tank senders. They should be checked for a certain resistance at 10 different positions to make sure they are accurate. One of the problems is the winding of the wire resistor. The wire inside a factory original is not linear. They wind the wire closer together at one end to match the rate of drop of the float. This keeps the gauge reading to match the shape of the tank and float arm angle. The last sender that I took apart that was a repro was not made this way, the resistance wire was wound evenly down the whole length.