70 GTX gauge problems

[maxwell1]

HI all, my gtx has got me fooled, replaced dash voltage reducer to a new solid state one. Fuel gauge basically shows empty when tank is full (has a new fuel tank sending unit with ground strap) Temp gauge shows cold, even when warmed up ( has 5 volts at temp sending unit) Oil pressure shows 20-30 lbs at idle ( placed a true gauge at block I have 60 lbs at idle) any and all help welcomed Thanx Max

 

[Photon440]

Hi Max, welcome to the forum! :wav:

Sorry, can't give advice on the dash, but everyone here has problems with the new fuel tank sending units.

 

[okiemopar]

I want in on this because I'm having trouble with my RR too. Started car and oil pressure was 60# amp gauge pegged out and oil pressure went to 20#. I may have to order new gauges for mine.

 

[bee71]

I'm wondering if those electronic VR units have a quality problem. I had a 68 Fury and got one that was the old style that mounted on the firewall and it went bad.

 

[nm9stheham]

Does your voltmeter jump around at all when you check at the output of the temp sensor wire at the engine, or does it read a steady approximate 5V? (And when I say 'jumping around', I mean the reading really changes a lot form moment to moment, not just a fraction of a volt.) Are you measuring the voltage at the temp sensor wire with it connected to the sensor or disconnected?

Can you post a link to the one you bought and I will look at it. I am only familiar with the ones from RTE. All the symptoms you describe could be a low voltage from the IVR.

Is the new IVR properly grounded at the dash? And do the instrument lights work right? (That is a good sign of a proper cluster ground.)

 

[maxwell1]

Does your voltmeter jump around at all when you check at the output of the temp sensor wire at the engine, or does it read a steady approximate 5V? (And when I say 'jumping around', I mean the reading really changes a lot form moment to moment, not just a fraction of a volt.) Are you measuring the voltage at the temp sensor wire with it connected to the sensor or disconnected?

Can you post a link to the one you bought and I will look at it. I am only familiar with the ones from RTE. All the symptoms you describe could be a low voltage from the IVR.

Is the new IVR properly grounded at the dash? And do the instrument lights work right? (That is a good sign of a proper cluster ground.)

The IVR is from Mega Parts made by charger specialties I believe. No the volt meter does not jump,my dash lights work. I measured the voltage at the temp. sending unit from the connector to ground. I also ran a ground wire from the back of the IVR to ground thanx Max

 

[Grabinov911]

Take a look through this thread and see if maybe it offers any insight. You and I have apparently had a lot of gauge problems in common!

http://www.forbbodiesonly.com/moparforum/showthread.php?32770-Temp-Gauge-Temperature-Gauge

 

[nm9stheham]

The IVR is from Mega Parts made by charger specialties I believe. No the volt meter does not jump,my dash lights work. I measured the voltage at the temp. sending unit from the connector to ground. I also ran a ground wire from the back of the IVR to ground thanx Max

Hmm my post from last night did not 'take'.

OK that IVR is a steady 5v, not a pulsed 12v type. So your readings make sense, and there is electrical continuity through the temp gauge at the least. However, you should have a lot less than 5V at the temp sensor when warmed up and connected.

Warm up the engine, and disconnect the temp sensor wire from the sensor, and use the ohms function of your meter to check the temp sensor resistance to ground. It should be around 25 ohms +/-. If it is much higher, then it is bad. If OK, then the gauge is electrically OK, but has a mechnical problem.

You can use the same process on the fuel tank: check the voltage at the tank with the wire disconnected to see if is is 5V. Then check the fuel sender resistance to ground with the wire disconnected; it should be in the low 70 ohm range near empty, in the mid 20 ohm range at half, and 10-12 ohms if full. If that is good, then the guage probably has mechanical issues.

Oil pressure is the same deal.

 

[maxwell1]

Thanx I will try this over the weekend and report back. again thanx Max

 

[maxwell1]

Hmm my post from last night did not 'take'.

OK that IVR is a steady 5v, not a pulsed 12v type. So your readings make sense, and there is electrical continuity through the temp gauge at the least. However, you should have a lot less than 5V at the temp sensor when warmed up and connected.

Warm up the engine, and disconnect the temp sensor wire from the sensor, and use the ohms function of your meter to check the temp sensor resistance to ground. It should be around 25 ohms +/-. If it is much higher, then it is bad. If OK, then the gauge is electrically OK, but has a mechnical problem.

You can use the same process on the fuel tank: check the voltage at the tank with the wire disconnected to see if is is 5V. Then check the fuel sender resistance to ground with the wire disconnected; it should be in the low 70 ohm range near empty, in the mid 20 ohm range at half, and 10-12 ohms if full. If that is good, then the guage probably has mechanical issues.

Oil pressure is the same deal.

Well I did all the resistance checks on all three gauges and my numbers are exactly as you say..... you mention my gauges have a mechanical issues please explain..... Thanx MAx

 

[nm9stheham]

If you would, please confirm that you read well under 5V at the temp sensor with it connected and warmed up (voltage readings wuold be good). And if you have a voltage reading at the tank sender with it connected, that would be good to know along with the fuel level. Having the voltage readings would help to make sure if there is something amiss with the resistive windings in the gauges.

The gauges work thermo-mechanically; there are small resistive windings wrapped around bimetallic strips. As the sensor resistance changes, the amount of power flowing into these windings varies, and the strips bend. The free end of the strips engages the gauge needles near their pivots, and move the needles back and forth. You can see the movement here in some later VW gauges: http://www.nls.net/mp/volks/htm/fuel_ga.htm

So the strips can be damaged or the mechanical aspects of the movements. And, if the resistive windings have shorted turns, then the heat will be low and the gauges will not move as it should.

 

[maxwell1]

Finally got back to testing things out ,with the motor warmed up, key on , motor off, I get 5 volts between temp. gauge wire and the temp sending unit,so Iam guessing my gauge is faulty???? what do you think thanx Max

 

[nm9stheham]

Well, that is not exactly the test you need to run. First, with the key in RUN, measure voltage from the temp sensor wire, with the red (+) lead of the voltmeter on that wire while disconnected from the sensor, and the other meter lead to chassis ground. If you still get 5 volts, then that says the voltage regulator is working and it is getting through the temp gauge (but the temp gauge could pass this voltage but still not work if it breaks in a certain way, as discussed).

Then warm up the engine to normal operating temp, and then
- use the resistance scales on the meter set to 20 to 200 ohms or a similar low ohm range,
- disconnect the temp sensor wire from the sensor,
- and read the sensor resistance with one lead on the temp sensor connection and the other on the temp sensor metal case, and see what you get.
- You ought to get 10 to 40 ohms or thereabouts. If so, then the temp sensor is working and the gauge is the likely culprit.

It takes a simple electrical setup to do a simple test of the gauge; that equipment existed 'back in the day', but is not hard to set up.
- Order a 22 ohm leaded resistor from Mouser or a similar place (radio Shack is dead, doggone it).
- Hook that between the temp sensor lead and chassis ground
- The temp gauge should indicate around mid-range with the key in RUN.

 

[maxwell1]

Just got back from a run did the ohm check at the sender and I got 20 ohms Thanx Max

 

[markbob]

Maxwell

Sorry to say but did u install the sending unit upside down?

Plz don't take offense..... I've done lots of stuff like this....

Good luck with fix

MB

 

[maxwell1]

No offense taken.I wish it was something that simple. My fuel gauge shows typical MOPAR fashion 5/8 on gauge means full. my bigger problems are temp and oil press, temp shows 0 all the time, oil pressure barely off bottom peg when I know I have 50 psi. Thanx for looking MAX

 

[nm9stheham]

OK, Max, I re-read all the last 10 or so posts. Looks like we concluded long ago that you have a constant 5V output regulator, and the temp sensor is reading at 20 ohms warmed up. ; I kinda lost track of all the info from November.

If you can mange to get a 22 ohm resistor and run the last test that would complete the testing. But it certainly looks like the gauge has issues.

 

[Durandal25]

I want in on this because I'm having trouble with my RR too. Started car and oil pressure was 60# amp gauge pegged out and oil pressure went to 20#. I may have to order new gauges for mine.

Ground issue sir.

 

[maxwell1]

OK,first of all I want to thank nm9steham for all the help, couldn't have pulled this off with out you. I changed out all my gauges, and now I have the following Fuel gauge shows 7/8 tank when full, Temperature gauge is spot on, Oil pressure shows about 7-9#s low, think I will change out sending unit to see if that helps. Thanx Max

 

[kiwigtx]

OK,first of all I want to thank nm9steham for all the help, couldn't have pulled this off with out you. I changed out all my gauges, and now I have the following Fuel gauge shows 7/8 tank when full, Temperature gauge is spot on, Oil pressure shows about 7-9#s low, think I will change out sending unit to see if that helps. Thanx Max

I think 7'8" on a FULL tank of gas is a fair starting point for your fuel gauge. What you need to do is see if you have 'full scale deflection' on your fuel sender unit. In other words, check to see if the float arm is able to travel to the maximum arc while installed inside the tank. Not an easy task, but it can be done. Depending on the supplier/manufacturer of the sending unit, you may need to either bend the float arm, or adjust the length of the arm. My one has a grub screw for arm length adjustment, so that was easy. Remember, if you shorten the arm, the readout along the gauge scale will change in time - you may notice while on a trip that 3/4 to 1/4 takes less time than it previously did.

Hope that helps. :icon_thumright: