70 Challenger rallye gauge problem

[moparman70rtse]

My oil pressure gauge is going all the way up past the H, and my fuel gauge is going past the Full line.
I'm not sure what the problem may be. The fuel tank is not full. I think only 4 to 6 Ga. is in it. And i really don't know what's going on with the oil gauge. I recently had the oil press. ga. rebuilt.
The shop the car was in installed the cluster back into the car.
Any idea what could cause this to happen?

Thanks,

[Chryco Psycho]

Often a mismatch between the sender & gauge , the sender is not putting enough resistance into the circuit so it reads higher than normal , common problem with most replacement fuel senders . The oil sender could be similar problem or if you have a High pressure oil pump it may be reading correctly , the gauge is only supposed to read 70 PSI or so max , I have seen a lot of mopars make 100 psi on a cold start up dropping into the 80 psi range warm

[moparman70rtse]

That's possible. The fuel sender is fairly new, but still could be bad. I'll replace the oil sender and see what happens. No High Pressure oil pump installed.
Any way of testing the fuel sending unit without removing from tank?

[FY1Cuda]

You can get the fuel sender out without dropping the tank, but it is awkward.  You have to take the muffler heat shield off (if you have it on), and to do that, you have to loosen the exhaust pipe hanger. 
Is your voltage limiter good on the back of the gauge cluster?

[moparman70rtse]

Yeah, I have muffler shields, but not a problem to remove.
Voltage limiter is on the back of cluster. I replaced org. about 3 years ago with a new modern type. I can't remember the company name (actually I think it was called dashworks), but I don't think they are in business anymore. I didn't think about it, but I need to look under dash, I think a red light should be blinking on the limiter if it's working although I'm not 100% convinced that's it because only the two gauges are not right. At least I have a few different things to check.

[moparman70rtse]

Ok, I'm starting to wonder if it's a ground issue. I tried turning the key without starting the engine and the gauge still rose all the way up.
As far as I know the needle shouldn't of moved. The fuel gauge needle moves, but I believe it would when key is turned. The fuel gauge goes all the way past full mark and I only have 4 to 6 gal of fuel so this may or may not be a sending unit issue. The water and amp don't move with key on.
Now, I'm not good at electrical so I'm asking, where should I check for ground issues?

Thanks

[Racer57]

Ok, I'm starting to wonder if it's a ground issue. I tried turning the key without starting the engine and the gauge still rose all the way up.
As far as I know the needle shouldn't of moved. The fuel gauge needle moves, but I believe it would when key is turned. The fuel gauge goes all the way past full mark and I only have 4 to 6 gal of fuel so this may or may not be a sending unit issue. The water and amp don't move with key on.
Now, I'm not good at electrical so I'm asking, where should I check for ground issues?

Thanks

Get a piece of wire and fasten it or hold it directly to the gauge cluster and to somewhere near by like the pedal mounts or something that you know is a good ground. This will by-pass all other grounds that may be bad and will let you know if grounding is an issue.  If you have a piece of wire that's long enough, run one directly from the neg post on the battery to the cluster. That's what I did this winter and it helped me clear up a lot of issues.

[JayBee]

I just duplicated that "fuel gauge goes past full" scenario on my car by grounding the blue wire that goes to the sending unit. 

I only have about 3 or 4 gallons in the car right now. Makes me think your blue wire is shorted to ground or you have a shorted sending unit. Try pulling the wire off the sending unit and see if the fuel gauge still pegs. It's a simple check and may just lead us to something.

[moparman70rtse]

Get a piece of wire and fasten it or hold it directly to the gauge cluster and to somewhere near by like the pedal mounts or something that you know is a good ground. This will by-pass all other grounds that may be bad and will let you know if grounding is an issue.  If you have a piece of wire that's long enough, run one directly from the neg post on the battery to the cluster. That's what I did this winter and it helped me clear up a lot of issues.

I was just thinking the same thing. I was also thinking if the sending unit itself is not making a good ground since the engine was repainted Car will be back in my garage in a couple of days so I'll give those a try, hopefully before the car goes back out to have the vinyl top installed.

[moparman70rtse]

I just duplicated that "fuel gauge goes past full" scenario on my car by grounding the blue wire that goes to the sending unit. 

I only have about 3 or 4 gallons in the car right now. Makes me think your blue wire is shorted to ground or you have a shorted sending unit. Try pulling the wire off the sending unit and see if the fuel gauge still pegs. It's a simple check and may just lead us to something.

John, that sounds like a very good idea. As I said on previous post, I'll hopefully be able to check in the next couple of days.
Just wondering though, how would the sending unit itself be shorted?

Thanks,
Gabe

[Chryco Psycho]

damage to the wound coil resister on the unit

[73EStroker]

To verify what CP has said try getting a 10 or 20 ohm 1 watt resistor and connect it in series with the sender at the tank. If the gauge indicates less fuel add perhaps a higher resistance till it is accurate around halfway. That will be better. Then cover it all with heat shrink sleeve with the epoxy in it so that it seals against moisture and you are good to go.