Fuel Gauge not working

[ajarofclay]

First point... YES, I know there are plenty of threads out here regarding this but they all differ and who has time for that. I'm already pulling my hair out.

That said, Here's where I'm at.

1. This car has basically been sitting in the garage for roughly 40 years.
2. I have had the cluster out to change bulbs which is a Friggen Nightmare if you ask me. Having to drop the wheel down, lack of wire length etc but I did disconnect the main loom and feel it is back together securely. Could be wrong. I don't know if the gauge was working before that as the tank was empty.
3. As some other threads have shared, I checked the ground strap, It was all a bit grimy under there but I took it off, cleaned all surfaces and reinstalled. No luck
4. I also pulled of the gauge wire, cleaned and reinstalled.

Does anyone have any other ideas before I tear out the seat again, drop the wheel and wrestle that dash open again? Sorry if I seem a little short; This car deserved to be on the road and I'm aggravated.

 

[Murray]

Did you ground the sender wire? This will cause the gauge to read full.

 

[67Dart273]

Well the absolute FIRST THING IS, WHAT are you working on? A 1932 Ford Mistang? How 'bout a hemi powered air raid siren? No I mean it. Really

Year make and model, and IS THIS a standard or Rallye cluster? An' yeh. It matters

Also, do you have a service manual/ wiring diagram? IF not run over to MyMopar.com and look around. You may have to settle for Plymouth vs Dodge or the other way 'round.

 

[ajarofclay]

No, It's reading Empty and I just put 5 gallons of fuel in it.

 

[mopardude62]

If it’s been sitting with the tank empty for 40 years, the inside of the tank and sending unit are probably completely rusted!

Even after adding 5 gallons of fuel, I’d guess the pickup tube is rusted shut and you won’t be able to pull from the tank!

 

[67Dart273]

No, It's reading Empty and I just put 5 gallons of fuel in it.

And we still have no idea WTF you are working on. Would you mind telling us?

 

[ajarofclay]

Well the absolute FIRST THING IS, WHAT are you working on? A 1932 Ford Mistang? How 'bout a hemi powered air raid siren? No I mean it. Really

Year make and model, and IS THIS a standard or Rallye cluster? An' yeh. It matters

Also, do you have a service manual/ wiring diagram? IF not run over to MyMopar.com and look around. You may have to settle for Plymouth vs Dodge or the other way 'round.

It's actually a 1972 Demon 340. If you notice, that's like the 1 manual they don't have and this car has a mix of stuff on model years on both sides along with some one year only stuff. In my experience, I've only seen 1 dash panel on these cars though mine does have a seat belt buzzer/light.

 

[ajarofclay]

If it’s been sitting with the tank empty for 40 years, the inside of the tank and sending unit are probably completely rusted!

Even after adding 5 gallons of fuel, I’d guess the pickup tube is rusted shut and you won’t be able to pull from the tank!

It did have some fuel in it which I drained out through my electric pump and have since removed and reverted back to stock. It starts and runs, fuel gauge just isn't reading. I do agree though sitting that long there might be some kind of an issue with the float being stuck.

 

[ajarofclay]

And we still have no idea WTF you are working on. Would you mind telling us?

I'm here looking for help. You may be the smartest man in the room but feel free to drop out of the conversation if you're going to be an asshat

 

[72bluNblu]

I'm here looking for help. You may be the smartest man in the room but feel free to drop out of the conversation if you're going to be an asshat

And that gentleman is one of the foremost experts on wiring and electrical issues on these old Mopars. I’m sure he could tell you exactly how a ‘72 Demon is wired, if you’d bothered to open with that.

And I’m sure he was TRYING to help you, but the wiring on these cars is different from year to year, model to model, and even by options (in this case, rallye dash or not, before you added the ‘72 demon part).

If you want useful help the first thing you should always post when asking a question is the year, make, and model of the car you’re working on. It’s really, REALLY, simple. Without that even if someone wants to help they’re not going to be able to.

If you want help, especially technical help on a 53 year old car, you should be willing to answer some questions. We don’t have a crystal ball.

 

[67Dart273]

I'm here looking for help. You may be the smartest man in the room but feel free to drop out of the conversation if you're going to be an asshat

I asked you a question and you ignored it. This forum is a two way street. NObody pays ANY of us to stop in here. Your statement claiming something special is mostly incorrect, at least for most of the basic wiring. I don't keep up with the options but over the years some cars could be had with the optional Rallye cluster. We need to know IF YOU HAVE THAT. The reason is simple. The Rallye clusters have the regulator device that operates the gauges, INSIDE the fuel gauge

What gauges does your car have? Does it have a factory OIL PRESSURE gauge? If so you have a Rallye cluster. If it only has a fuel, temp, and ammeter, and a warning lamp for oil pressure, it is the "standard" gauge.

The 72 Plymouth manual over at MyMopar will suffice for most of the wiring in the car.

The basics of the gauges: This includes temp and fuel, and oil pressure on Rallye clusters, except the location of the regulator device. These are variously called "gauge limiter" or IVR or "instrument voltage regulator"

Basically you have power from the ignition switch fed to the cluster, powering various items, as well as the instrument limiter. That feeds REGULATED power of sorts to the temp and fuel gauges, which are a "hot wire" type of thing, that operate on approx. 6V pulsating

From there each of the gauges sender terminals go to ground through whichever sender we are working on, IE temp or fuel.

You wan't to be careful as you can damage the gauge units, as well as the IVR SOMEONE ALREADY mentioned to access the fuel sender wire at the tank, devise a way to ground that, and then turn the key to "run." The gauge should quickly peg. Don't allow it to be connected more than necessary. If the gauge pegs, I would start with a gummed up fuel sender.

If nothing happens, try the same thing with the temp sender in the engine bay. If it does not move, you likely have a problem with the cluster PC board, a wiring harness issue, or a bad IVR.

WE STILL NEED TO KNOW if you have a standard or Rallye cluster

 

[KeithH]

Check the fuel sending unit in the tank just took mine out cause I was having a similar issue and found the float was deteriorate and was filter was very dirty.

 

[dodgemahal]

Dude, 67dart273 is your man. Don't throw him away. He has been a tremendous help to me, especially with a gauge problem I had recently. He's the best resource you will ever have. Sorry if I sound terse.

 

[ajarofclay]

Good Lord, Help me...

I guess it's my turn to write an essay.

To All:

First off, it wasn't a personal affront on 67Dart, It was a Reaction. I've seen far too many crass responses and ongoing sniping on these threads over the years and it's frustrating. Same goes in all walks of life. I try to treat everyone with respect. If you look back, I finished the initial post with "Sorry if I seem a little short; This car deserved to be on the road and I'm aggravated." My apologies...

Before I get too far, THANK YOU FOR THAT THOROUGH RESPONSE, 67! I hope I am able to do something with it.

67 and 72, I realize in my haste, I dropped the ball on what my car is, Sorry. I find myself being pulled every which way lately for time and after at least a month, I finally got a minute to ask the Subject question. I'm an old single guy with with plenty on my plate, not a lot of dollars and even less time. On top of that, I've got a habit of routinely putting my projects aside to help other people (probably a big reason why I get testy when people get short or impatient with others)

67, I wasn't ignoring your question, I simply wasn't there. It may have looked like it because this site is one of about a half dozen that I keep a tap open all the time. I was pulling carpet in my bedroom along with a thousand staples to get it ready for a friend to install some new stuff. I did look back and tried to respond on my phone which can be a PITA and took responses in order starting with MURRAY's. My response to you was going to be a little longer so I decided to finish the room and address it once I could get to my CPU. By the time I got to that, you had already repeated the question...

A factory oil pressure gauge is probably the key to the rallye cluster question. Mine Does Not have one; I installed an aftermarket gauge 50 years ago. I don't know if I've ever seen a factory oil pressure gauge in this model year. Does anyone know if there was a rallye option in '72 as that was the initial year of lowering compression and "de-smogging".

Before I get too far, I should mention that I have plenty of Mechanical aptitude but electronics ARE NOT my forte to say the least. That said, how would you suggest I "devise" a way to ground the fuel sender wire and if necessary the temp sensor wire? I get really apprehensive about electricity for just the reason you state about damaging the unit. I've burnt enough wiring in my day.

Thanks in advance for any more info.

 

[Mattax]

OK. Factory fuel gage and coolant temperature gage work by sending a pulsed electrical current through the gage and sending unit. The current has to make it to ground to for the gage to work.
So that's why someone suggested briefly grounding the output wire from the gage.
Better is to use a 10 or 15 ohm resistor. 10 ohms would simulate a full tank while reducing the risk of burning out the gage.

If you're behind th edash or have the panel out, a very quick and crude check of the gage alone is to measure the resistance between the input and the output. IIRC it should be abut 15 ohms.

There are some good MTSC on the gage & sending units.

Thermal-Electric Gauges (Session 227) from the Master Technician's Service Conference

Homemade gauge test tool, C-3826

I finally dug through the junk box, went down to Radio Shack, and built myself a copy of the Mopar C-3826 guage test tool. It's a little crude, but hey, I'm not going to "show" it. According to what I can find, the three test resistances for senders (in the C-3826 tool) are L...

www.forabodiesonly.com

If you're curious about the options that could have been on your car, look in here

The 1970 Hamtramck Registry Library Page (1970 - 1974)

 

[WymanV]

A '72 isn't going to have a Rallye cluster unless someone swapped one in (like I did ). '71 was the last year for them.

IVR=internal voltage regulator? I've seen this mentioned in a few threads but can't nail down the context.

 

[RedFish]

This standard a-body panel has fuel and water gauges and a mechanical limiter plugged in the back. If the water temp gauge works the limiter is working.

 

[ajarofclay]

OK. Factory fuel gage and coolant temperature gage work by sending a pulsed electrical current through the gage and sending unit. The current has to make it to ground to for the gage to work.
So that's why someone suggested briefly grounding the output wire from the gage.
Better is to use a 10 or 15 ohm resistor. 10 ohms would simulate a full tank while reducing the risk of burning out the gage.

If you're behind th edash or have the panel out, a very quick and crude check of the gage alone is to measure the resistance between the input and the output. IIRC it should be abut 15 ohms.

There are some good MTSC on the gage & sending units.

http://[URL][URL]https://www.web.imperialclub.info/Repair/Lit/Master/227/Cover.htm

[/URL][/URL]

http://[URL][URL]https://www.forabo...reads/homemade-gauge-test-tool-c-3826.179517/

[/URL][/URL]

If you're curious about the options that could have been on your car, look in here

http://[URL][URL]https://www.hamtramck-historical.com/library.shtml

[/URL][/URL]

Thank you, Sir! This will be extremely helpful. Great link for the service guide! Fantastic! My gut feeling is that it is on the mechanical end with the float but if not, I feel comfortable with this information.

 

[ajarofclay]

A '72 isn't going to have a Rallye cluster unless someone swapped one in (like I did ). '71 was the last year for them.

IVR=internal voltage regulator? I've seen this mentioned in a few threads but can't nail down the context.

I thought the same but wasn't positive. I just know I'd never run across one to my knowledge. Thanks

 

[CRUZE 418]

His fuel tank may not be a rusted mess, leaded fuel from back then seems to coat them. Unless it was full of water. Only a look will tell.

 

[ajarofclay]

His fuel tank may not be a rusted mess, leaded fuel from back then seems to coat them. Unless it was full of water. Only a look will tell.

I think I'm "probably" okay with that or at least I hope so. The car had been sitting for about 40 years but always indoors in attached garages with no rusting on the body, frame etc. That doesn't mean there wasn't water in the tank though. Even the tank looks good on the outside anyway. Crossing my fingers

 

[MOPAROFFICIAL]

First point... YES, I know there are plenty of threads out here regarding this but they all differ and who has time for that. I'm already pulling my hair out.

That said, Here's where I'm at.

1. This car has basically been sitting in the garage for roughly 40 years.
2. I have had the cluster out to change bulbs which is a Friggen Nightmare if you ask me. Having to drop the wheel down, lack of wire length etc but I did disconnect the main loom and feel it is back together securely. Could be wrong. I don't know if the gauge was working before that as the tank was empty.
3. As some other threads have shared, I checked the ground strap, It was all a bit grimy under there but I took it off, cleaned all surfaces and reinstalled. No luck
4. I also pulled of the gauge wire, cleaned and reinstalled.

Does anyone have any other ideas before I tear out the seat again, drop the wheel and wrestle that dash open again? Sorry if I seem a little short; This car deserved to be on the road and I'm aggravated.

How about the low voltage regulator in the back of the cluster, have you replaced that yet?

 

[dmopar74]

Fuel gauge don't work, check the float. I've found that's usually the culprit. You can pull the sender, ground it, and see if the fuel gauge works.

 

[MOPAROFFICIAL]

I thought the same but wasn't positive. I just know I'd never run across one to my knowledge. Thanks

Do you have a pulsing voltage at the wire to the sender or not? If not, replace the ivr/lower voltage regulator the plugs into the back of the cluster. One of the wires piggy backs to it.. so also make sure that wire is still plugged in. Your welcome.

 

[ajarofclay]

How about the low voltage regulator in the back of the cluster, have you replaced that yet?

No, I have not. That's the can of worms I'm hoping not to get into. I had the dash out to change out all my bulbs and that was Nightmare IMHO. Had to drop the wheel to free up some space. Wiring was very Taut and I actually cracked a cornere of where it wraps around the column. It glued together really well without anything noticeable but I don't want to have to do that again if I can help it.