No reading on Gas Gauge, What to do??

[prayers1 153]

As I mentioned in post #22, I had 12v to Pin # 7 & 11. I did this with the key on, not to ACC.

 

I'd also check continuity from the ground (pin 8) to the case of the CVR.

I don't understand. Where does pin#8 end and what does it do?

[Midlife 814]

Midlife, do you happen to know the resistance on the wire that supplies

the 12 volts? The diagram shows it as being a resistance wire, I have always wondered ? never thought to check it when I had one in front of me.

 

15 ohms.

[Midlife 814]

As I mentioned in post #22, I had 12v to Pin # 7 & 11. I did this with the key on, not to ACC.

 

I'd also check continuity from the ground (pin 8) to the case of the CVR.

I don't understand. Where does pin#8 end and what does it do?

 

Pin 8 is the ground line and is needed by the CVR to switch from 12V to 0V so that it can put out a consistent 5V; at least it works that way before Ford started using a resistance wire to the CVR. It is also needed for the dash lamp grounds. Yup...checked schematics and the CVR does need a grounding point.

[prayers1 153]

How do I test pin#8, at what point to where for continunity. If my hazards, turn signals and dash lights work, doesn't this mean I'm getting a good ground.

Edited October 11, 2013 by prayers1

[prayers1 153]

From reading about CVR's on the web, it reduces the 12v current to the oil, temp & fuel gauges to around 5v. There is a simple test to test those gauges while out of the dash.

 

"Use a 6V Lantern battery to see if that cause the gauge to sweep? Actually 3V should give you about a quarter of the way up the scale and 4V about 3/4 of the way. The lantern batter is just a bit easier to use due to the spacing of the terminals."

Is this information correct?

Edited October 11, 2013 by prayers1

[Mach 351 10]

I had a similar problem with my gas gauge and it ended up being my CVR. Before I discovered it though, I went through all the tests and didn’t have much luck tracing the problem. I’m electrically challenged. I read on a web site (can’t think of the name) of a man who repairs vintage gauges that the internals are the same on both sides of the cluster. The only difference is what is displayed on the face. I swapped out the gauges Gas for Temp (Deluxe cluster w/Tach) and had the same problem with the other gauge. By process of elimination I then went with the CVR. My CVR was only a year old at the time, and one of those new fancy digital ones.

[danno 128]

I have been out of the loop on this one, so maybe you have already checked for this? The place where the gas guage screws to the flexible circuit card can be an issue. With the instrument panel removed from the car, unplug the CVR. The change your voltmeter to ohms, and measure the resistance between each of the pins of the gauge and the Metal chassis supporting the gauge cluster. Your ohmeter should indicate an "open circuit". An open circuit is the same as what the meter shows when it is set for ohms and you have nothing connected to it.

 

If you do this test, and your ohmmeter gives you anything less than 100 ohms, I know what your problem is.

[det0326 179]

How do I test pin#8, at what point to where for continunity. If my hazards, turn signals and dash lights work, doesn't this mean I'm getting a good ground.

 

Yes if you have instrument lights your ground should be OK.

The reason you need this ground at the regulator too, as in all DC circuits is to simply complete the circuit back to the battery ground.

[det0326 179]

From reading about CVR's on the web, it reduces the 12v current to the oil, temp & fuel gauges to around 5v. There is a simple test to test those gauges while out of the dash.

 

"Use a 6V Lantern battery to see if that cause the gauge to sweep? Actually 3V should give you about a quarter of the way up the scale and 4V about 3/4 of the way. The lantern batter is just a bit easier to use due to the spacing of the terminals."

Is this information correct?

 

If you simply want to check the gauge, you could put low voltage such as a flashlight battery 1.5 volts to see if you get a deflection but be sure you have the polarity right or it will deflect in reverse and could cause your calibration to be off a bit. You said in an earlier post that you have

12 volts at pin 11 and you have ground to pin 8 so with everything connect like it is suppose to be you are not getting 12 volts at the input to the CVR. Well IMO there could only be 4 reasons 1. You have an open circuit from pin 11 to input of CVR 2. you have an open ground to the CVR which as Midlife stated is pin8 to the case of the CVR. 3. Your CVR is bad. 4 You could have something grounded somewhere on the output side of the CVR . You would think that if something was grounded on the output side of the CRV that you would smell smoke but I think that is why the wire at pin 11 is resistance protected. This is just my opinion I could be wrong.

[prayers1 153]

I did as all suggested and got crazy numbers, nothing made sense. I went down to my Mustang parts guy, he didn't have a new CVR, but 2 used ones attached to a circuit board. He gave them to me for free. When I went to replace the CVR, the push in button on the new circuit board fell off. NOW WHAT! This Circuit Board was new and made in the USA, as it's stamped on the back. I was very disappointed in the quality, I knew it was loose and I have been babying it. Apparently when it was made they didn't crimp & center it correctly on the contact spot.

 

Well maybe this was a blessing in disguise, I had another circuit board that had some oxidation, I cleaned off all contact points with steel wool, installed it on the cluster, used what I thought was the best of 5 CVR's and turned the key. For the first time I saw the fuel gauge needle move up to E then back down. I Grounded the wire to the sending unit directly to the neg. side of the battery and the needle went to full. Ok, now I'm thinking I have a bad sending unit. I thought to try the newest CVR that I have, turned the key and it slowly went to 1/4 of a tank. I tested the sending unit wire and it went to Full.

 

If the sending unit was bad, why did the needle move from E to a 1/4. I have about 10 gallons of gas and the needle drops below the E, it reads an 1/8 before it reaches E.

 

I think I sould leave well enough alone.

What do you think???????

 

Hers a picture of the New Circuit Board

[det0326 179]

I did as all suggested and got crazy numbers, nothing made sense. I went down to my Mustang parts guy, he didn't have a new CVR, but 2 used ones attached to a circuit board. He gave them to me for free. When I went to replace the CVR, the push in button on the new circuit board fell off. NOW WHAT! This Circuit Board was new and made in the USA, as it's stamped on the back. I was very disappointed in the quality, I knew it was loose and I have been babying it. Apparently when it was made they didn't crimp & center it correctly on the contact spot.

 

Well maybe this was a blessing in disguise, I had another circuit board that had some oxidation, I cleaned off all contact points with steel wool, installed it on the cluster, used what I thought was the best of 5 CVR's and turned the key. For the first time I saw the fuel gauge needle move up to E then back down. I Grounded the wire to the sending unit directly to the neg. side of the battery and the needle went to full. Ok, now I'm thinking I have a bad sending unit. I thought to try the newest CVR that I have, turned the key and it slowly went to 1/4 of a tank. I tested the sending unit wire and it went to Full.

 

If the sending unit was bad, why did the needle move from E to a 1/4. I have about 10 gallons of gas and the needle drops below the E, it reads an 1/8 before it reaches E.

 

I think I sould leave well enough alone.

What do you think???????

 

Hers a picture of the New Circuit Board

 

 

Measure the resistance on the sending unit and see what it is?

This would tell you if your sending unit is good or bad. MikeTyler

may be exactly right but I though that I read somewhere that it is suppose to measure 10-14 ohms full and somewhere around 70-74 empty.

[Midlife 814]

Test continuity from the pin itself to a good rust-free place on the chassis. On the circuit card, follow the trace to where the CVR resides---I believe the case of the CVR should touch the ground trace. You can check continuity from the connector flap to that area.

[prayers1 153]

My daughter has a Volleyball Tournament all day tomorrow, so I can't get to the car for a couple of days. I'll test the sending unit continuity then.

 

Midlife- Electrical testing is one of my weak points. Please simple explain what your wanting.

 

Test continuity from the pin itself to a good rust-free place on the chassis

Are you refering to pin#5, Yellow/wht stripe for the sending unit. What I did is test continuity from pin#5 to the end of that wire and it Beeped.

 

On the circuit card, follow the trace to where the CVR resides---I believe the case of the CVR should touch the ground trace. You can check continuity from the connector flap to that area.

Are you meaning the ground side of the CVR on the printed circuit? If so, test at the Ground side of the flap to where?

[Midlife 814]

I was referring to the ground pin (#8). Test from pin 8 on the dash cluster connector to the chassis ground: it should read approximately 0 ohms or beep.

 

Test for beep between the case of the CVR to the flap on the circuit card that matches pin #8 (ground) on a removed dash cluster or on a dash cluster with the connector removed.

[prayers1 153]

With the dash cluster disconnected, I tested pin# 8 on the wire bundle to ground on the body and got a tone. Then, I tested pin# 8, to the back of each (2) metal snap button for the CVR while the CVR was still connected with the snap buttons. I forgot which one toned but one did and the other didn't

 

I now realized that you wanted me to probe the metal case of the CVR instead of the button. What I did for now, is that sufficient?

 

What were you trying to determine?

[Midlife 814]

For the CVR to work correctly, it must have a ground. There's a bi-metallic strip inside that moves from the 12V to the ground tab, cycling back and forth, making a 5V average. Since one of the tabs read ground, I would surmise that the strip is at 0V and making contact with the grounding trace.

 

Are you sure you have gas in the tank? *G*

[prayers1 153]

Yes, approx. 10 gallons. I have to drain the tank for another reason, then I'll know exactly how much gas there was.

 

Would it be safe to say that everything is in good working order and I can put the dash back together.

 

If things checked out with the dash side, then why would the needle sweep to full when the wire to the sending is placed to ground?

[prayers1 153]

Out of curiosity, I checked pin#8 to the case of the CVR and got tone.

 

Hopefully, I can drain the tank today and check the fuel gauge needle.

[det0326 179]

Out of curiosity, I checked pin#8 to the case of the CVR and got tone.

 

Hopefully, I can drain the tank today and check the fuel gauge needle.

 

Check out this link

 

[prayers1 153]

Update-

 

I drained the gas and found approx. 6.75 gallons.

 

I then tried to see what the gauge read and now it reads in between 1/4 & 1/2 tank. It rose an 1/8th. Now what?

 

I'll check the manual test on the sending unit when I pull it out.

 

Any other opinions!

[det0326 179]

Update-

 

I drained the gas and found approx. 6.75 gallons.

 

I then tried to see what the gauge read and now it reads in between 1/4 & 1/2 tank. It rose an 1/8th. Now what?

 

I'll check the manual test on the sending unit when I pull it out.

 

Any other opinions!

 

I would check the continuity at the tank sending unit by using an ohm meter connecting one lead to the terminal where the wire connects and the other lead to the metal case of the sending unit. What we are looking for would be a reading of around 60 ohms since you know the tank is empty. Check this before pulling the sending unit out may save you some work.

[prayers1 153]

I have a fuel contamination concern, which I think mud dobbers got into the tank while at the body shop, so I'll have to take the sending unit off to look inside. Hopefully, I'm wrong and the tank is clean.

 

I did take a peak of that YouTube Video, it's self explanatory which I like. Thanks!!!!

[Midlife 814]

Yes, approx. 10 gallons. I have to drain the tank for another reason, then I'll know exactly how much gas there was.

 

Would it be safe to say that everything is in good working order and I can put the dash back together.

 

If things checked out with the dash side, then why would the needle sweep to full when the wire to the sending is placed to ground?

 

That's exactly what is supposed to happen. The sending unit is a variable resistor that works in a backwards way. Resistance is high (78-83 ohms) when the gas tank is low and resistance is low (13-17 ohms) when the tank is full. By grounding the sending unit line, you have removed all resistance and the gauge will peg high.

[prayers1 153]

OK, then why didn't the gauge read empty when the key was turned on. It actually went 1/8th higher than before. See post #45

[Midlife 814]

By fiddling with connectors, you may have made a good connection...I dunno...magic?