gas gauge has just started staying at 3/4 tank but I know its less than that in the tank.

had a similar problem last year with it. I put a new fuel sending unit on, a new (old) 12 volt gauage , AND a constant volt reducer that goes behind the intrument panel (80 bucks from ford dealer ouch!!)
turns out the volt reducer was fried and was the culprit last year

I guess tonight I pull the dash and start taking things apart again.
Anythoughts or suggestions?
Todd
ps I saw the gauge climb quick to full and drop back down to 3/4 while idling at a stop sign this morning

 

Todd -

The gage in my 56 was doing something similar and, like you, I thought that the problem was different resistance between the gage and the sender. That still might be it, but I solved the problem using a more purely mechanical approach. I realized that the sender and gage must have been in the ball park with each other and that I could either put a resistor in the sender line to dial it in (George helped me scope that out) or I could recalibrate the sender to match the gage. I did the latter.

I took the sender out of the tank and reconnected the sender-to-gage wire using a jumper. I also used a jumper to ground the sender to the chassis. I laid the sender on a piece of cardboard marked for the tank height (I stuck a tape measure down thru the sender hole to find an accurate dim for the height). I put the sender on the line for the tank top and started working the float arm up and down. The gage responded. I adjusted the float arm length and the up/down position of the float pivot clamp until full up and full down on the float arm read full and empty on the gage. Reinstalled the sender. All has been perfect ever since. The whole operation took about an hour.

You could try this method before tearing into the dash. Might fix the problem, doesn't cost any money and it's pretty easy. Just a thought...

 

thanks for the Info Randy-thats a really good solution to calibrate a gauge accurately.

My gauge has been really accurate since I replaced all the pieces I mentioned above (done last fall) It's been great for 800 miles and many tankfulls of gas. The "spike jump" of the gauge to full this morning might be some kind of clue whats going on..i Don't know for sure

 

Usually when Ford guages " Spike", it is the CV regulator that's on the way out. You can get them thru NAPA also. That Ford dealer banged you hard on the part. ( I'm a Ford parts guy)

Barry

50 F-1

 

thanks for the info Barry
I thought I tried NAPA last fall when I was looking for one and was told I need to get those from the dealer

If I fried the one I just put in, I wonder whats doing the frying

I'll pull the thing from behind the dash panel and pop off the casing to see if the fine wire is truley fried

 

also my temp gauge stayed near full hot when I started the truck coming home from work tonight. there is definately something wrong with the guages

i pulled the inst panel and removed the volt regulator
the fine wire wound around the bimetal bar "looked" fine
not fried
i guess i'll pull the gas and temp gauges apart next to see if the fine wires are broke or burnt on those

if nothing there, i guess i'll try buying another regulator for hopefullly less than 80 bucks

kinda stumped

 

I'd check the ground wires on the temp gauge. My gas gauge is working and it's accurate, but it drives me crazy because the needle bounces between 1/4 tanks.

 

Barry you were right NAPA has the part under a different number-the price was 26 bucks compared to the dealers price of $70 !!!!
I installed the new regulator and wala---everything works fine

THis is a great site
Thanks everybody

 

For the gas, temp, and oil gauges, you can test them by applying 1.5 Volts dc across the leads. The gauge needle should come to center. If it moves toward center, but comes to rest elsewhere, try adding a low resistance in series. If that helps, then wire that resistor in series with the gauge. The Ammeters (battery gauge) are inductive. Without the engine running, switch on headlights, and the gauge should show discharge. If it shows charge, the wire is passing past the gauge backwards, and you will need to reverse it.