Gas Gauge Fix

Electrical & Ignition

  1. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    The gas gauge has never been right on my car. I think one of the previous owners replaced the sender years ago and as most replacement senders seem to work, the gauge read low. A full tank was just over half way on the gauge.

    I found this on the web a while ago... TechnoVersions - MeterMatch for Analog Gauge Correction
    Basically, this went in the sender wire from the tank and you could adjust it to make the gauge read correctly. They have two versions, one with a LED warning light and one with a built in voltage limiter.

    The Ford guys have the same issue. Here's an article that the MeterMatch website linked to. http://technoversions.com/MeterMatch-Fairlane.pdf

    It seemed like a simple solution to a common problem. So... I got in touch with them, asked a few questions and I ordered one. MeterMatchGuts.jpg

    One thing that has to change is the voltage limiter. The old mechanical/electrical piece won't supply the constant output that the gauge will need to work correctly with the MeterMatch. They address that on their site, and have a version with the built in regulator, but I've also found out that the newer electronic voltage limiters will work well with it... So if you've already replaced the limiter, the installation gets a bit easier.

    I installed mine a couple nights ago. My gas gauge would never read too much above a 1/2 and I have been resetting my trip odometer every time I fill up to double check myself as the gauge drops towards empty.

    I figured I had about 3/8 of a tank left and used the MeterMatch to correct to that level. I used the "mid low" point to set that. Since we've had rain every day since I did this (more like a monsoon), I haven't been able to fill the tank and set the high point. I figure I have to use a little math and figure gas mileage and set the "mid high" point after using about a 1/4 of the tank. Here it is hanging out of the dash.

    WagApQW.jpg

    So... We'll see what happens and I'll report back on how it works. With the Carlisle trip coming up, I should run a couple full tanks of gas through the car.

    I also wired mine to use the existing "low fuel" warning light. It was a little more complicated and involved the use of a relay to turn the light on... I'll show how I did that a little later.
     
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  2. live4theking

    live4theking Old Man with a Hat

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    That's pretty cool. My gas gauge reads low as well. Never more than 3/4 full.
     
  3. commando1

    commando1 Mr. Normal FCBO Gold Member

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    FCBO Member Product Review. I like that.
     
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  4. tbm3fan

    tbm3fan Senior Member

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    Cool. My sender was replaced but I also rarely read above 1/2 full. I have also changed out to an electronic voltage regulator for the instrument panel so this could be just what is needed.
     
  5. OneEyed

    OneEyed Active Member

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    I'm still curious what the actual problem is though. Are all the sending units out of spec now? Or all the gauges?
     
  6. CBODY67

    CBODY67 Senior Member

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    The fuel sender is a simple resistor. As the contact on the fuel sending unit moves, it moves across a resistance coil. More resistance, lower readings, etc. There are also some senders, possibly model-year specific, that have different basic resistance ranges than others. IF they used a universal sender, or modified one from another model year, incorrect readings might result. Looks like the MeterMatch customizes the resistance for the vehicle it's installed in?

    Also, be sure the ground strap on the fuel tank segment of the fuel line, which the sender grounds through, is in good condition. Might need to ground it directly to the body rather than through the fuel line. The strap looks like two clamps joined by a metal strap, as I recall, with a tab on each end for "metal contact".

    CBODY67
     
    Last edited: Jul 1, 2017
  7. commando1

    commando1 Mr. Normal FCBO Gold Member

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    I've gone through four gas gauges. The original and three "NOS".

    There was nothing wrong with the original. I was putting in all new guages so might as well put one of those on.
    The first NOS guage was wayyyyy off.
    As was the second.
    The third is dead on.

    High probability the first two so-called NOS guages were actually warranty replacements stuffed back in the box.

    Owning used C-bodies in my youth, I always took it matter-of-factly the guages were way off in the reading.
    Fill it up, the needle was pegged off the guage and stayed there for 200 miles until it suddenly dropped to below 1/2. 1/3rd meant almost empty, 1/4 meant empty and below that meant I was on fumes.
     
  8. mr. fix it

    mr. fix it Old Man with a Hat

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    I had to shorten my Sending unit to get it to go the full swing.
    Once I did that, replaced the wiriing and cleaned all the grounds the Polara now reads full to empty and back again!
    It will be interesting to see if this does the trick
     
  9. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    I think that is correct that the replacement manufacturers are using a "universal" sender. This seems to be a problem across the board with all the models. I did a little reading and after talking to some early Mustang guys, the problem isn't just with Mopars either...

    A lot of us have gone through all the suggested fixes and they sometimes help. Grounding the sender is huge on the list and one of the first things that should be checked.

    Then you have the 40-50 year old gauge too.....

    If this works as well as it is promised, this can end up being a pretty good fix.
     
  10. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    I really think it's mostly the sending units, but the gauges weren't anything to write home about when new... They don't get better with age either.

    It may just really be the combination of the two... But I haven't known a single person that was happy after putting in an aftermarket sender.
     
  11. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    There is that too... Some of the C bodies I drove had good gas gauges... and some didn't. I learned early to fix the ground as that was quite often the problem, but they really just never worked all that well in the first place.
     
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  12. commando1

    commando1 Mr. Normal FCBO Gold Member

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    To this day, my fuel Guage never gets below 1/4.
    I've carried that neurosis for fifty years.
     
  13. rapidtrans

    rapidtrans Senior Member FCBO Gold Member

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    I watch the odo also. 200 miles and i fill-up. 25 gal tank leaves a sizeable reserve even at 10mpg.
    My gauge doesn't move. Goes to just over half full upon ignition/engine on and stays there till i shut off ignition. I'm thinking ground issue either at tank or gauge connection.
     
  14. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    Following up....
    I filled up the car the other day and tried setting the the "full" set point. I made a mistake by trying to set the "mid-high" set point first. I should have known better.... I haven't been retired that long...

    So... I reset everything to the default settings and took a step back.

    I know that at full, my sender measures about 30 ohms resistance, so I had a place to start.

    I was going to gather up some resistors, but I decided to take a look at Ebay first... and there I found it.. A $20 Eico decade box.
    Eico-1171-resistance-decade-box-img.jpg

    For those of you that don't know what this is... It's a box full of resistors. You dial up the resistance you want (0-99,999 ohms). In this case, I'm going to check my gauge and then use it to set my Meter Match.

    The gauge checked great...

    Here at 23 ohms, it's at the halfway point where it should be.

    0a9ElzD.jpg

    8NytTLs.jpg
     
  15. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    Next I set the upper set point. Since I knew my sender measured 30 (should be 10) ohms when full, I dialed the decade box up to 30 and set the high point.

    A good sender should measure 74 ohms when empty. I decided that it was off 20 ohms on the high side, it's probably about the same on the low side... or somewhere in between. I decided to set the low set point at 84 ohms and see how it works.

    So far... so good.

    I drove the car a little and the gauge went to 1/2. My first thought was the Meter Match had crapped out... but after a little checking, I've decided the sender is acting up. Measuring the resistance of the sender, I figure it's about double what it should be for the amount of gas in the tank. It appears to be an intermittent problem... Probably just worn or dirty. I looked at the wiring and all appears good.

    So.... It's too late to screw with it... It's going to Carlisle Thursday.... I'm going to look for a new sender when I'm there.

    I'm still very positive about the Meter Match... When my sender works, it's good. Some clean up of the old one or replacement and I'll reset everything. The decade box paid for itself.
     
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  16. Fury440

    Fury440 Old Fart with a dead Fury FCBO Gold Member

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    Are you measuring the sender resistance at the dash? There is a ground strap jumper between the tank and the hard fuel line. This connection is part of your sender circuit. Turns out on many cars there is a second jumper at a splice in the hard line where the front clip is joined to the main body. This second jumper is sorta hidden by the transmission mount. Mopar grounding systems suck.
     
  17. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    Kind of... Actually at the plug at the drivers side A pillar.


    Yes, that was addressed a couple years ago as step one in getting the gauge to work correctly. It wasn't the issue and I even looked at the jumper last week.

    I've added ground wires to senders on other cars, although not this one just yet. A sheet metal screw on the face plate and then to the body is a much better way than the factory. When I get back and pull the sender out, that will be one thing I will do with this car too. Even a new sender....

    This issue is acting like a bad wiper on the rheostat in the sender.

    I didn't know there was a second jumper. Learn something new every day!
     
  18. Fury440

    Fury440 Old Fart with a dead Fury FCBO Gold Member

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    As I say, don't know if all cars have the second jumper. However, those that do also have a short piece of hose connecting the hard line ends. Same jumper as used between the sender and the hard line back sat the tank. Not sure of the purpose, maybe allow easier front clip connection at the plant or maybe to isolate vibration from the engine. A lot of "old" cars have a lingering fuel smell which we associate with smelly carbs, but in many the problem is the front hard line splice hose is weeping.
     
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  19. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    Following up....

    Since my trip to Carlisle, I haven't had the opportunity to get back to this. Life has been getting in the way...

    The sender crapped out completely on the Carlisle trip.

    Once the stars aligned.. Meaning a low tank of gas and some time to spend, I removed the sender yesterday.

    The ground was good. A ground wire had been run to the body to rule out any issue a couple years ago and that was still intact. All wiring looked good etc.

    The sender turned out to be an original Chrysler part, not the aftermarket part I thought it would be.

    Checking it with my trusty DMM, I found that the sender worked intermittently at best. When it did work, the resistance was very high, even at "empty". Taking it apart, it was obvious that the rheostat windings were dirty and the wiper arm had lost most of its tension and was quite worn. There's some corrosion at the rheostat connection that may be contributing to the intermittent problem too.

    HQAEBVG.jpg
    G78aFVF.jpg

    After cleaning it up and bending the wiper so it made better contact, I could get the sender to work. The resistance is off... ~120 ohms at empty and ~40 ohms at full. I might be able to adjust the position of the wiper a bit by bending it and get that to read better, but even if I got it right, given the condition, it's on borrowed time.

    The Spectra FG148A is the part all the suppliers sell as the replacement and since they all seem to be drop shipping from the manufacturer, it came down to price. Amazon Prime had it for $48 + NYS sales tax with free shipping so I ordered a new one. BTW, that was half of what some places wanted for the same piece!
     
  20. Ripinator

    Ripinator Senior Member

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    Yer gonna need another manicure. . .