Temp & fuel gauges - what am I overlooking?

[67Dart273]

I keep telling you that test resistors are the way to verify this. These gauges are not that accurate, but if you heat the engine---and you believe your mech gauge, then the sender should read about the same as the "mid scale" test resistor, And you should be able to apply that test resistance to the sender wire and get the gauge to read mid scale.

Same thing with fuel. Just measure the sender resistance as it sits. Whatever it is, estimate what the gauge should read with that resistance. And check the gauge with test resistances in place of the sender.

One reason manufacturers used the limiter system is to attempt to offset the swing in system voltage. AKA 12 something in the winter at idle, with lights on, up to 14V when RPM is up. The limiter helps "average" those swings and helps keep the gauges somewhat accurate

 

[Super-Cuda]

Well Bob,

Like the old saying goes, if you have eliminated all other options, whatever is left, no matter how improbable, it must be the answer.

I have to say..

I have fixed numerous gauge cluster problems.

If this turns out to be two faulty senders, it will be a first for me.

 

[Super-Cuda]

I keep telling you that test resistors are the way to verify this. These gauges are not that accurate, but if you heat the engine---and you believe your mech gauge, then the sender should read about the same as the "mid scale" test resistor, And you should be able to apply that test resistance to the sender wire and get the gauge to read mid scale.

Same thing with fuel. Just measure the sender resistance as it sits. Whatever it is, estimate what the gauge should read with that resistance. And check the gauge with test resistances in place of the sender.

One reason manufacturers used the limiter system is to attempt to offset the swing in system voltage. AKA 12 something in the winter at idle, with lights on, up to 14V when RPM is up. The limiter helps "average" those swings and helps keep the gauges somewhat accurate

Hey 67Dart273,

Please correct me if I'm wrong here but wasn't the whole idea of the newer electronic IVR"s to provide a constant 5 volt output to the gauges even with fluctuations to the 12 volt input?

I built my own IVR and it works perfectly

. Steady 5 volt output. It takes longer for the gauges to respond on start up but that's the only issue and a very small one.

I do agree totally with your test procedure using resistors to simulate the sensors

I for one will use that test procedure in the future.

Cheers!

 

[Vinny]

Put it back together. Heated up the old sender, plugged it in and grounded it, and the dash responded.

Reconnected the new one, ran a ground from the hex (body) to an intake bolt and confirmed continuity between the sender and battery.

I ran the engine with that extra ground connection to where the mech gauge read 160, and the dash gauge never moved. Ditto the fuel gauge. I guess I've got two failed senders, both new, at the same time. I'm skeptical but there it is.

BADDA BING!

 

[Uncle Bob]

I removed the new temp sender, tried to get an ohms reading out of it hot and cold, no dice. Put the used sender in it, gauge now works. It's far from accurate but I never really cared about the dash temp gauge anyway - I really just need the fuel gauge to work.

Next stop - fuel sending unit.

 

[67Dart273]

Hey 67Dart273,

Please correct me if I'm wrong here but wasn't the whole idea of the newer electronic IVR"s to provide a constant 5 volt output to the gauges even with fluctuations to the 12 volt input?

I built my own IVR and it works perfectly

. Steady 5 volt output. It takes longer for the gauges to respond on start up but that's the only issue and a very small one.

I do agree totally with your test procedure using resistors to simulate the sensors

I for one will use that test procedure in the future.

Cheers!

I think you missed what I was trying to say. Even the purpose of the old electromechanical IVRs was to attempt to regulate the gauges, as the actual 12V system voltage was going from BELOW12 on a cold, rainy, winter night, with heater, wipers, etc---to 14 and sometimes a bit above.

 

[67Dart273]

A better way to do gauges is to use what is called a bridge circuit. Some gauge meters are in fact dual windings, 3 terminal. They are in a bridge circuit, and system voltage is less critical. The clue to such gauges is a ground for the gauge, not for the lamp

 

[Uncle Bob]

I'm working on the fuel sender now. I checked out everything inside the kick panel and all is well. I checked the ground for the sending unit. I do not have a grounding strap, but it is grounded through the tank (I did not pad under the tank straps), and there is continuity between the sender and the shock bolt so I'm pretty secure in that being OK. Before today I also had an auxiliary ground wire that I don't need so I took that out of the way.

A test probe flashes when connected to the sender wire so I know it's getting power. I didn't check grounding the wire at this end, because it acted as expected in the kick panel and there is proof of continuity via the flashing test probe.

Then I checked the ohms* at the sender, and it showed 60. That should be about 1/2 tank, so I checked the gauge, but it's still only rising up to the edge of the E line.

Then I checked the ohms from the sender in the kick panel, and it was 75, So that agrees with the gauge but 15 is 25% of 60 which seems like a pretty extreme difference. I don't see any corrosion but who knows how the wire could be damaged between points A and B. Should I jump a new length of wire between the kick panel and sender and check again? I think I will - it won't hurt.

*The way I checked ohms was to probe the sender (or wire) and ground. Is that the right way to do it?

 

[Uncle Bob]

I'm working on the fuel sender now. I checked out everything inside the kick panel and all is well. I checked the ground for the sending unit. I do not have a grounding strap, but it is grounded through the tank (I did not pad under the tank straps), and there is continuity between the sender and the shock bolt so I'm pretty secure in that being OK. Before today I also had an auxiliary ground wire that I don't need so I took that out of the way.

A test probe flashes when connected to the sender wire so I know it's getting power. I didn't check grounding the wire at this end, because it acted as expected in the kick panel and there is proof of continuity via the flashing test probe.

Then I checked the ohms* at the sender, and it showed 60. That should be about 1/2 tank, so I checked the gauge, but it's still only rising up to the edge of the E line.

Then I checked the ohms from the sender in the kick panel, and it was 75, So that agrees with the gauge but 15 is 25% of 60 which seems like a pretty extreme difference. I don't see any corrosion but who knows how the wire could be damaged between points A and B. Should I jump a new length of wire between the kick panel and sender and check again? I think I will - it won't hurt.

*The way I checked ohms was to probe the sender (or wire) and ground. Is that the right way to do it?

I ran a separate wire from the sender to the kick panel area, trying to use about the same length of wire and it showed 76+ Ohms again. Then I checked under the car again, and this time it read same as it did in the kick panel. So either I'm not using the meter correctly or the sender is bad.

The car should have about a half tank in it. I filled it up while out the last time then drove less than 50 miles.

The wire has a ring terminal on it. The hose/clamps in the foreground plug off the return line and the supply line is just behind that.

 

[RedFish]

80 ohms = no needle movement. 73 ohms should = empty hash mark. 34 ohms should get close to the 1/4 tank mark but,,, your model gauge, from 1/2 tank down, even with the OEM sender, never was very accurate. The same 73, 23,10 tester was still used. Looking for what 1/4 tank is on your gauge just because you have the tools to do it is really only for fun. I have to say, all the time wasted over 2 bad senders is ridiculous imo. Need to know,,, the wire terminal for the fuel gauge was a booted 90 similar to what you have at temp sender. Yes a hex nut with toothed washer works but DO NOT OVERTIGHTEN. Turn that studs and get a fuel leak and likely break the connection other end too.

 

[Uncle Bob]

80 ohms = no needle movement. 73 ohms should = empty hash mark. 34 ohms should get close to the 1/4 tank mark but,,, your model gauge, from 1/2 tank down, even with the OEM sender, never was very accurate. The same 73, 23,10 tester was still used. Looking for what 1/4 tank is on your gauge just because you have the tools to do it is really only for fun. I have to say, all the time wasted over 2 bad senders is ridiculous imo. Need to know,,, the wire terminal for the fuel gauge was a booted 90 similar to what you have at temp sender. Yes a hex nut with toothed washer works but DO NOT OVERTIGHTEN. Turn that studs and get a fuel leak and likely break the connection other end too.

I know all that but thanks.

FWIW when I first put it in the the original connector wouldn't plug in. I don't remember exactly why but I think the stud is too big.

You can't imagine how much I wish I had never pulled the cluster out. Now I can't get the speedo cable plugged back in Seat comes out today so I can get my old decrepit self under the dashboard. It seems like the cable's in the wrong place somewhere because it's too far to the passenger side, and I am not inclined to pull the cluster again to re-route the cable.

 

[67Dart273]

You know all that yet you can't get it to work. We have been beating our heads trying to give you advice, and you don't directly address this. I don't know where your are or where you've been. Worse, I don't know where you are going. It seems to me you are chasing your tail. This is the last I'm going to say

I already told you to wire up the cluster on a bench, use the test resistors, and get the cluster/ gauges to work on resistors. If that works then you have gotten that far. If it does not check out, you need to address it before you even think about the rest of the vehicle

The sender wires are simple, and there are not that many terminal points

The fuel sender wire has t he terminal at the cluster connector / pc board so THAT is an issue. It has the left kick panel connector and that can be an issue. The sender wire can get pinched where the back seat goes. The sender connector can be corroded/ damaged, and the sender can have several problems

The temp sender wire has the same type cluster /pc board connector, then the terminal at the bulkhead / firewall connector and the same type sender connector as the tank

AFTER YOU get the CLUSTER tested on resistors, you should be able to install it, and then retest using resistors AT THE SENDER connectors

Once that checks out, the only thing left is senders themselves, and possibly the sender grounding. This can be a real issue with fuel tanks, and the temp sender is easily damaged by over-tightening.

 

[Uncle Bob]

You know all that yet you can't get it to work. We have been beating our heads trying to give you advice, and you don't directly address this. I don't know where your are or where you've been. Worse, I don't know where you are going. It seems to me you are chasing your tail. This is the last I'm going to say

Address what? I know you can't twist that stud, I may not be a supergenius like you but I'm not an idiot. You know that if the connection was broken, I wouldn't be getting any Ohms reading, right?

I did everything suggested in this thread, followed up on all of it, and appreciate all the advice and it was help that pinpointed the problem to the sending unit. Yes I do know the problem is the sending unit. Don't you by now?

 

[RedFish]

Many have trouble with the speedo cable. Disconnect neg' battery cable.There is 1 screw holding the fuse box in place. Carefully move the fuse box. Pull headlight switch to on. Reach in and push the button that releases the switch stem. Pull the stem, remove the switch bezel nut, move the switch. Sit on a 5 gallon bucket in the door jamb and have a go at that cable attach. You can get a arm all up in there. The cable does need to be routed to the instrument as straight as possible.