Gauge issues

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Mike 71X
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Gauge issues

Post by Mike 71X » Thu Jul 12, 2018 7:28 pm

Got the car back together and started and after a few days the gauges all pegged out. Someone suggested changing the voltage limiter on the gauge panel so ordered a new solid state one. It corrected the problem for a few days but now have the opposite issue, the gauges all read low... some barely come up at all. Could it be the new voltage limiter failed but the opposite way and is not letting enough voltage through? Or is there something else we should be looking at. I tried a stock voltage limiter out of a parts car and get the same result, gauges barely work. Possible that voltage limiter is no good. Any suggestions on what to check. Will be going out to check output voltage from the limiter shortly.

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Re: Gauge issues

Post by 71bird » Thu Jul 12, 2018 11:02 pm

What brand of regulator did you get?
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Mike 71X
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Re: Gauge issues

Post by Mike 71X » Fri Jul 13, 2018 9:57 am

Says Charger Specialties. Came from Mega Parts.

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Re: Gauge issues

Post by 71bird » Fri Jul 13, 2018 12:15 pm

The best limiter is the Real Time brand. I'd call Charger Specialties and ask them if that is the ones they sell. I have heard that these solid state regulators can read low, I'm not sure of that, but I have heard of it. I have the Real Time regulator, and I feel like mine read low also, but on the other hand, if the sending units and gauges aren't original that could have something to do with it to. My car came with what the service manual calls a resistance wire that is between the oil siding unit and the wiring harness and nobody can tell me what it does.
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Mike 71X
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My Cars: 1971 GY8 Plymouth GTX
Location: South Dakota/Minnesota

Re: Gauge issues

Post by Mike 71X » Fri Jul 13, 2018 1:07 pm

Thanks for the response. I don't think it's the real time brand, no LED indicator light on it. Testing the voltage at one of the gauges we got 4.45. From what I've read it should be 5. Not sure if half a volt is enough to make them read low. Bench testing the old limiter it reads 12 volts so no surprise there why the gauges were pegged. Can't get a bench reading on the limiter from the parts car so guessing that is probably junk. Grounding the temp gauge will max it out so its at least responding but it will barely come up with the engine hot. Prior to the original limiter failing it would read a little less than half. Fuel is full but that gauge will only read a little over half now. The oil pressure appears to be OK, starts at 3/4 on cold engine and drops to half when warmed up. That would lead me to think maybe the fuel and temp gauges gott fried enough they are out of calibration? I've never heard of calibrating these gauges before but as I've been researching this have seen some mention about it. If the solid states actually tend to cause gauges to read low it's interesting that this didn't happen until after a week.

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Re: Gauge issues

Post by 71bird » Fri Jul 13, 2018 4:56 pm

Are all the gauges OE gauges? Is the fuel sending unit an OE unit? If I were you, I'd replace that reg with a RT one cause they are designed so that if they fail it will go to the off side and won't fry the gauges. Let me look at my service manual to see if it says anything about voltage. I think 4.5 might be to low. I have the original reg from my car, tell me how you had it hooked up to bench test and I'll ck mine. Is this a rallye set up, or standard panel?
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Mike 71X
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Re: Gauge issues

Post by Mike 71X » Fri Jul 13, 2018 5:36 pm

Gauges are original, fuel sending unit is not. Here is some new info. First off, a mistake on our part. The 4.45 was measured with key on but car not running. With car running it was right at 5. Called Charger Specialties, they said it should be within 4.95-5.05. Said they had never gotten one back for low voltage but that if by some chance it was only putting out 4.5 the gauges would read low. So I believe the limiter is not the issue. The oil pressure gauge appears to be OK. I read somewhere the oil pressure, temp and fuel gauges all work on the same resistance scale, they just have different reference marks. So we got the idea to swap the sending unit wires between gauges. Hooking the fuel sending unit to the oil pressure gauge gave us a "full tank" indication on the oil gauge. Similarly, hooking the temp sending unit to the oil pressure gauge gave us a needle position similar to where the temp gauge was running before all this started. Conversely the oil pressure sending unit hooked to either of the two gauges in question gave minimal/zero reading. So our conclusion at this point is those two gauges got messed up when the original limiter failed. We spent some time running the car with the oil pressure gauge disconnected and using a mechanical gauge so our thought is that's why that one still works while the other two are having issues. They are reading a small level of input though so I'm hoping I can just send them off for recalibrating.

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Re: Gauge issues

Post by 71bird » Fri Jul 13, 2018 6:01 pm

Are the oil and temp sending units new?
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71bird
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Re: Gauge issues

Post by 71bird » Fri Jul 13, 2018 9:25 pm

I looked at the service manual and without a special tester there is no way of testing the sending unit, or the gauges.
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Mike 71X
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Re: Gauge issues

Post by Mike 71X » Fri Jul 13, 2018 10:05 pm

Oil, temp and fuel sending units are new. Found an article on AllPar that said the fuel sending unit should show around 8.5-10.5 ohms when the tank is full. We measured just over 10.

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Re: Gauge issues

Post by 71bird » Sat Jul 14, 2018 11:05 am

New sending units may the the problem. Back in the day, the oil and temp sending units had different ranges for different set ups, but new ones now don't offer that, and unless you know what you need you don't know which NOS one to get, we are kind of in the dark on putting the right one in the car. If you don't have a service manual you can down load one for free on mymopar.com. I found what I think is my original oil and temp sending units and this winter I'm gonna put them in and see if they still work. Where did the fuel sending unit come from?
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Mike 71X
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Posts: 19
Joined: Sun Mar 11, 2018 12:22 pm
My Cars: 1971 GY8 Plymouth GTX
Location: South Dakota/Minnesota

Re: Gauge issues

Post by Mike 71X » Sat Jul 14, 2018 11:27 am

Not sure, I'd have to check with the guy who did the restoration. My gut tells me that's not our issue as they have been working flawlessly since they got the car running a month ago, temp sitting right where you'd expect it to be and the fuel gauge responding accordingly. This all started after the original limiter failed last week. I think he even changed out the temp sending unit again before we figured out the limiter was bad.

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road chicken
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Re: Gauge issues

Post by road chicken » Fri Jul 20, 2018 9:55 pm

The regulator should be putting out a 5 volt DC pulse. The calibration is just to tune the gauge to the sending unit. This is a supply issue.
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road chicken
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Re: Gauge issues

Post by road chicken » Mon Apr 01, 2019 10:01 pm

http://www.mopar1.us/instrument.html

for those savy enough to build it..
4th generation B bodys- there is no substitute.
68 383, Street Demon 750, RPM top end,484/284/108 poo poo cam "-5 spd 4:10 SG, 4whl disk, Helwig Anti-Sway, Poly bushings,Firm Feel Box, HD Linkage, 1" t-bars, 7 leafs Springs

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