1958 ranchero fuel gage prolem

[unclevinny]

new sending unit, new napa rin1 CVR new wire from sender to gage when i turn the ignition on the gage goes to full [tank is full] but then drops to 1/4 and then rises to over half and repeats this till i shut the key off anyone know what might be causing this? Thanks

[rotorwrench]

I'd have to see what the original sending unit looks like to give best information since I'm not familiar with the 57 models. If it had King-Seeley instruments then they were a current change based system instead of the resistance based systems that have been used in the modern era. To the best of my knowledge, there is no source for KS type sending units. The indicator gauges were manufactured to work on the current provided by the sending unit. When things went to 12-volt, they started using the pulsing current type constant voltage regulators to lower and stabilize the current draw of the system in order to keep current low which also affected the voltage according to OHMs law.

The modern replacement sender units are all rheostat devices that vary the current/voltage between the sender and the indicator. The indicators are calibrated for a different type of system so they don't always work to give good indications and many times it just can't be accurately compensated for the differences in the two devices.

There may be a problem with the constant voltage regulator too. It should be constant no matter what the configuration of the components is. The solid state CVRs are usually better than the old bi-metallic pulse types but I don't know what you have there.

I'd either look for a functional original type sending unit or I'd change the indicator and sending unit with compatible OHM value types. There are near a half dozen different Ohmic values currently available in sending units depending on the make & model of the system but there are also aftermarket systems available. Aftermarket set ups may not have a indicator that can be retrofitted to your application so it would take some research to find stuff that might work.

[5851a]

Sounds like bad cvr, cvr is a contradiction in terms since it varies. But a solid state type may work better for you. Ford gauges in general are slow responders and that worked well with the pulsating voltage. Maybe try an electronic version. What is your temp gauge doing at the same time? both are powered by the same source.

[cb]

When I was building my 57 ranchero I searched everywhere for a new sending unit with no luck, I tried using a 57 reproduction unit for a car which didn't work, tried bending the float rod to match the ranchero/wagon didn't work. Sent my original one out to have it modified to work that didn't work either. In case you didn't know the sending unit is specific to the 57-59 ranchero/wagon only because of the shape of the tank. I lucked out and found a usable one out of a 59 ranchero in a wrecking yard.

[Ford blue blood]

First thing, is the temp gauge working as it should? Both are fed from the little can regulator. If the temp gauge does not indicate as it should there is most likely a regulator issue. If the temp gauge works as it should disconnect the fuel gauge wire at the sending unit. Turn on the key, if the gauge does the same thing there is a problem with the wiring (a short will make the gauge run to full). If you have the stock wiring in the car disconnect the plug under the carpet at the top of the tunnel and repeat the test.

[rotorwrench]

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If it is a KS unit, I've used compatible units with a soldered modification of the float arm. Some of them have some odd shapes but wire can be manipulated to adjust and calibrate if necessary. The King Seeley units were very good units if that's what it has.

I've seen U-tube videos where DIY guys have gutted the CVR units and installed solid state CVR components. The old original chopper type bi-metallic units were pretty reliable but a lot of the new repro stuff is crap. After Echlin was bought out by Standard Motor Parts, I've been monitoring the net for Echlin related problems. It seems like the good stuff always looses out to the cheap stuff in the end.

[unclevinny]

Thank you for responding to my gage problem I have tested the CVR that cost me 71 dollars and the output side responds in the fashion with the voltage going from 5 1/2 volts down to 2 volts and then goes back up to 5 1/2 so i think i have got a off shore echlin production of junk!!! i will see if napa will take it back and return my money [less the 50% restocking fee] lol so i am going to look for a different way to go following your all experienced ideas again Thanks