Vette-kid

My 78 has a few gauges not working. Looking at the schematics and the troubleshooting book, it seems as if a few work (temp and Volts) then the rest should have power/ground as well. That narrows it down to gauges themselves or the PCB, or in the wire harness itself, no? Anything else im missing? Fuel gauge could be the ground at the sender. Is there another ground for each gauge that im not seeing?

mikem350

Go to www.willcox.com. He has great troubleshooting info and schematics.

Bloodzone

Just replaced my PCB because of lights and oil pressure gauge not working. This fixed my lights but the Oil pressure was still maxed out. Turned out Teflon tape on my sending unit was interfering with the grounding. Cleaned it off and gauge works perfectly. No surprise my clock is shot. I taped off the power to the clock on new PCB and let it go for now.

Vette-kid

hmm...hadnt thought of that, may have to give it a try. Although that sensor is a pain to get to!

79C3tnd

None of the gauges except for the fuel gauge and the clock (yes, my clock actually works!) work on my 79, and I have recently replaced the PCB as well. I feel your pain. I haven't started trouble shooting yet, but like you, I thought that the ground might be bad, but since the fuel gauge works, I am not sure what to think. I doubt that the ground on all the other 3 gauges is bad, but stranger things have happened...

Vette-kid

Ive been reading the wilcox guide and studying the wire charts/troubleshooting guide all morning. One thing I dont get on the Wilcox guide for the fuel sender: It mentions testing the resistance from the sending unit, Im not real sure where you would place the test leads in order to do that. Probably a real dumb question, but im not seeing it. If it ever stops raining here I could get out and actually work on this, until then Im stuck trying to figure out what to do first when it does stop (besides buy a boat...seriously, this is ridiculous). Can someone explain how that test would work? If you place one to the resistance terminal on the sender and the other to ground I dont see a circuit through the resistance to measure the Ohms.

0Willcox Corvette

Two L's... lol.. and I'll see your post faster..

Test the ohms wire connection from the sender to read the sender output.

This paper will show you exactly how to check the sender.

1977-1982 Corvette Fuel Gauge and Sending Unit Testing


-Willcox

Vette-kid

Ha, my bad! It makes sense now. I had been starting art that paper and the diagram too long! Guess i needed to step away from it for a moment. Thanks.

Vette-kid

Willcox, what does it mean when the needle goes straight up when doing the test. Removing the #1 wire my needle goes up and down...not to 3 or 4. Grounding it indeed moved the needle full left.

I haven't gotten part this stage yet as i ran out of time. But since it didn't respond exactly as you expect,i wanted to ask.

Also, the needle does bounce a little off E when driving, but never really indicates anything. Tank is full. There is a chance it is a wrong year gauge...my temp gauge appears to be 80-82, the car is 78. Can this have an effect?

0Willcox Corvette

Which test are you doing? If you start at the beginning of the paper and read to the end you'll get a full understanding of how to test both the dash unit and the sender.

For instance...

Pull the pink wire from the sender and test the prong coming out of the sender for ohms. If the tank is full as you say... the output should be somewhere around 90-100 ohms. If the tank is full and the ohms is say 10 then there is an issue inside the tank or the sender is bad

With the pink wire removed from the sender, turn the key on and see where the needle on the dash unit goes..

If the needle goes to full as indicted in the left upper picture below then ground out the wire and the gauge should go to E as shown in the upper right picture.

If the gauge responds in this manner then the dash unit is fine and the issue is something else.. (sender, sender ground).

If the gauge doesn't respond exactly in this manner then the issue is the gauge or the PCB. The picture below shows you the different scenarios possible with different gauge issues.

It's common for the bladder in the tanks on the 1978-1982 cars to separate from the side of the tank and allow fuel behind them. When this happens the bladder can actually impede the movement of the float arm on the sender.

Willcox

Vette-kid

I am doing your test...following the paper. When i pull the pink wire with ignition on, the gauge goes to half tank. Ground or and it goes past empty to the 9 o'clock position. I haven't had a chance to pull the gauge yet, but out sounds like either a bad gauge or pcb?

0Willcox Corvette

with the wire pulled you have no ohms input.. the gauge should go to just above the rivet on the face.. .if it doesn't then you have an issue in the dash unit.

Could be multiple things.. from the gauge to the pcb.

Willcox