| Ron3181 | -- 01-05-2020 @ 5:49 AM |
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I put in the new sending unit and the same thing occured again. That is with the motor rpm's are up the gauge goes all the way to full and will stay there as long as the rpm's are up (driving at 40 mph) By this time I know that the tank is not full and i am guessing there is just above half in the tank since I have driven around 60 miles since fill up. At idle the gauge shows just above half but when you start going again the rpm's go up so does the gauge reading and it stays up. Anybody have any ideals on what is going on. Thanks for the help.
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| 37RAGTOPMAN | -- 01-05-2020 @ 7:03 AM |
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HI was wondering if the car is wired correctly ? seems like when the generator is working the gas gauge goes up and when it does not it goes down ? I would recheck the wiring , does it have new wiring, or OLD ORIGINAL ? also you might have dirty connections ? or corroded ? were is the wire coming from that supplies voltage to the dash gauges ? get back to us, to see what you found, hope this helps, 1937RAGTOPMAN
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| trjford8 | -- 01-05-2020 @ 7:07 AM |
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Did you run a ground wire from a screw on the sender to a clean spot on the frame as suggested in your previous post? You also mention a "new" sender. Didn't you just need a new float? If you put in a new sender(reproduction?) they do not work well with the original gauge. Need some clarity on just exactly what you have done since your previous post.
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| Ron3181 | -- 01-05-2020 @ 8:36 AM |
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original problem was the float, I replaced the float and the gauge worked. however it did the same thing that the new sending unit is doing, that is the gauge goes all the way up at high RPM's and back down at idle to just above half which maybe the right level. All wiring is correct and new, no corroded connections. I did run the ground wire to frame with old unit and new unit. the new sending unit is a reproduction from Dennis Carpenter and they say the unit works with the original fuel gauge.
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| supereal | -- 01-05-2020 @ 1:31 PM |
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The problem is likely due to a rise in system voltage as the generator output goes up with engine speed. This is normally controlled by the large resistor mounted on the passenger side of the firewall. The resistance of this unit rises a system voltage goes up by heating the nichrome winding of the resistor. This not only affects the instruments, but prevents the ignition points and coil from burning up. Be sure your car has such a resistor, and that it is a genuine type. Put a voltmeter between a "hot" wire and ground to see what the voltage does as the engine speed rises before and after the resistor. There should be marked difference. You don't mention whether you car has been converted to 12 volts. If so, you need a "voltage dropper" in the feed to the gauges.
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| JayChicago | -- 01-05-2020 @ 8:33 PM |
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I believe the above information is NOT correct. The resistor does not affect the gauges. In 36 the hot wire feeding the fuel and oil gauges did come off the resistor block, but from the input terminal being fed from the ignition switch. It was just a convenient place to pick-up a switched hot source; the resistor itself does not come into play here. The effects of the resistor would only be at it's output terminal, which only feeds the coil. I don't see how the resistor could affect the gauges. UNLESS...the wire feeding up to the gauges was inadvertently put on the output terminal of the resistor block rather than the input terminal where it belongs. Then it would be fed after the resistor, and the gauges would be getting about 3 volts or less. I don't know if the gauges would work at all with only 3 volts. I wouldn't think it would be the symptoms described, the gauges would be getting 3 volts both moving or idling.
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| Ron3181 | -- 01-07-2020 @ 6:54 AM |
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Still no answer, gauge needle goes up when RPM"s go up comes down at idle. I now have NO ideal how much gas is in the tank. I can not get any steady reading on the gauge.
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| MG | -- 01-07-2020 @ 9:31 AM |
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Post some pictures of the old and new sending units you have....
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| JayChicago | -- 01-07-2020 @ 2:51 PM |
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RON3181 Sorry, I feel your frustration with this, but I think we are running out of ideas to help. Earlier TomO suggested you check voltage at the sender, and check ground at the sender. You posted you did run a ground wire to frame, but I didn't see anything about voltage there. I would be interested to know voltage at the sender, and if there is a substantial difference in voltage with engine at idle vs. driving . Can you put a voltmeter on the wire at the sender, and take readings at both engine RPM's? Do this with the wire disconnected from sender. Let us know what you see. This message was edited by JayChicago on 1-7-20 @ 4:57 PM
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| trjford8 | -- 01-07-2020 @ 4:09 PM |
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I'm beginning to think that the poster has an old repo sender and now a new repo sender. Photos would be good of both senders.
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| LarryK | -- 01-08-2020 @ 7:14 AM |
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I looked up the Dennis Carpenter sender on their website (Part No. 99A-9275). It is advertised as suitable for both 6V and 12V. Do the installation instructions specify any difference in the electrical hookup based on voltage? As a suggestion, you may want to check the resistance: it is specified as 88-94 ohms for an empty tank and 14-18 ohms full. Larry
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| JayChicago | -- 01-08-2020 @ 10:42 AM |
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New, perfectly good aftermarket senders are notoriously inaccurate. As we have learned from TomO, they use an entirely different technology than the original sender. I have an aftermarket in my car. It took a lot of trial-and-error improvising to overcome the sender's inherent shortcomings to get the gauge needle to show whats actually in the tank. But in this case it seems to be something different. The gauge is reading half at idle, then jumps to full when driving. And same symptom with two different senders. I didn't experience that, and I haven't heard of that before. This message was edited by JayChicago on 1-8-20 @ 11:16 AM
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