Inaccurate Guages on a 61.
Does anyone have any thoughts on why my gas guage needle is generally inaccurate, fluctuates with the turn signal and moves two needle widths toward "Full" when I press down and hold the brake pedal? Also, why does my temp guage read 20' hotter than normal when compared to a good aftermarket guage? I've tried a new sender to no avail.
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Re: Inaccurate Guages on a 61.
Run a separate ground wire from the sending unit on the gas tank directly to ground. That should solve that problem. As far as the temp. goes, good luck. I've tried several $5 generic TU-5 sending units as well as the $25 one from Lectric Limited with the same results - an inaccurate gauge. I don't have an answer for that one. -
Re: Inaccurate Guages on a 61.
Jim D's solution will certainly fix the problem.
You may first try cleaning the ground connection on the rear harness in the trunk, I believe on the left side. Cleaning the grounds on the rear lamps could help as well. This SHOULD solve the problem. If not, then do as Jim suggests.Comment
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Re: Inaccurate Guages on a 61.
Thanks, I'll try cleaning the grounds first.Comment
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Re: Inaccurate Guages on a 61.
Jim
You already got the answer to your fuel gauge problem. As for the temp, have you had the gauge rebuilt and calibrated? Mine did the same thing till I sent it out, now it tells correct temp according to my IR gun and extra temp gauge.
TerryComment
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Re: Inaccurate Guages on a 61.
No, I haven't had it calibrated. Where is a good place to have this done?Comment
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Re: Inaccurate Guages on a 61.
Thanks everyone for your help on this. Here's an update. I cleaned and inspected all ground connections in the trunk and again at the tank sending unit. Nothing noteworthy to report as far as corrosion, poor connections go but there was a slight improvement in operation. When I connected an additional ground wire to the sending unit the gauge now works fine.
I hate to resort to this kind of fix but is this the best I can hope for? It appears to me that the sending unit ground wire should have been designed with a heavier gauge wire.Comment
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Re: Inaccurate Guages on a 61.
Methinks you're fighting a 'ghost' here!
The gas gauge circuit is battery to gauge, gauge to tank sender, tank sender to ground. A series connection with the gauge being essentially an ammeter reporting the degree of current flow through that branch circuit.
These cars were built WELL before the advent of solid-state, three-legged, voltage regulator chips! So, the gauge WILL vary in lock-step to what battery voltage is supplied to it!
If your car is stock, it'll have a generator and electro-mechanical voltage regulator. The battery voltage will naturally vary from somewhere in the high 11 VDC to mid-high 12 VDC range depending on the age, condition and state of charge of the battery.
Next, generator's have a 'cut through' profile. That means the amount of power they deliver to charge the battery WILL vary with specific engine RPM and voltage regulator switching. Bottom line, expect the generator's contribution to charging the battery to fall between 0 VDC and something just shy of 15 VDC.
So, that says the supply voltage to the fuel gauge can/will vary from something like 11.5 VDC to 15 VDC. That's a 30% range!
When you're stopped at a traffic light, foot on the brake and turn signal engaged, the generator is essentially supplying NO charging current, the battery is at/near its bottom threshold. Plus, you're drawing current to supply the ignition, brake lights (headlights/tail lights IF engaged) AND the turn lamps are flashing on/off.
So, anyone who's had experience with these older cars knows the ammeter and fuel gauge pointer needles WILL vary/bounce under these conditions and then re-stabilize once you're reved the engine and gotten underway again...
Methinks you're asking for 1970+ era electrical system performance from a 1950-60's car. That's an unrealistic expectation...Last edited by Jack H.; July 26, 2009, 01:34 PM.Comment
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