rally gauges spiking to full?

[wigger]

i have rally gauges in my 1970 cuda, gauges are new to car. when key turned on all gauges spike to full.(fuel,oil,temp) It has a new voltage limiter. when i remove 1 wire off the fuel gauge the other gauges work properly. Ive added a better ground on fuel sending unit, didnt make a difference. did ohms test on sending unit, got no readings. would a faulty sending unit cause the gauges to spike full?

 

[challenger6pak]

Jim @Slotts may know what the issue is.

 

[Steve340]

A faulty sending unit would cause a problem in the gauge it was connected too, not peg out all three.
There should only be 5 volts to those gauges. I would check the voltage limiter or the fuel gauge itself.

 

[wigger]

A faulty sending unit would cause a problem in the gauge it was connected too, not peg out all three.
There should only be 5 volts to those gauges. I would check the voltage limiter or the fuel gauge itself.

voltage limiter runs 5-5.5 volts, when you connect fuel gauge voltage limiter runs at 9 volts. The fact the fuel gauge is spiking tells me its working ( maybe theres another way to test? fuel gauge)

 

[Slotts]

The first step I would ask you to try is unplugging both sides of the fuel gauge and take an impedance reading across the two terminals. A working fuel gauge should show the resistance of -20 Ohms. Then check each terminal separately to the gauge frame for ground. Both terminals to ground should show up as no impedance or O/L on a digital meter. I'll be curious to see what your readings are.

Jim

 

[wigger]

The first step I would ask you to try is unplugging both sides of the fuel gauge and take an impedance reading across the two terminals. A working fuel gauge should show the resistance of -20 Ohms. Then check each terminal separately to the gauge frame for ground. Both terminals to ground should show up as no impedance or O/L on a digital meter. I'll be curious to see what your readings are.

Jim

thanks for the reply Jim
i tested across the 2 connections and got a number of .01 ohms. tested between each terminal and gauge frame ground, no reading . I did this with ohms, wasnt sure if thats what you were referring to.
Andrew

 

[Slotts]

Hey Andrew,

Ok, let me help a bit with the meter types and settings. When I do restoration work on the Mopar muscle car electrical parts, I like to use an analog (needle sweep) meter. When using a digital meter on these parts, especially when trying to measure moving resistance readings, it is so much easier to see with an analog meter. When trying to measure moving resistance readings measure right up there with trying to read the actual price of the amount of gasoline you are filling at the pump. The reading is constantly updating and becomes very hard to see.

I am attach a couple of pictures showing the two types of meter settings and readings. The analog meter is set to read Ohms with the adjustable multiplier set to one. You can see I am reading the fuel gauge between - 19 to -20 Ohms. The digital meter is showing -12.4 at 200. If I run the multiplier up to 2K, I do see a similar reading as you have shown, .012 Ohms.

The whole purpose of measuring the fuel gauge by itself is to see the condition of the fuel gauge working or not working properly. Trying to see if there is a short or the fuel gauge is being grounded inside. With your measurement of each terminal on the fuel gauge to chassis ground is not showing a reading is a good thing and does not sound like your fuel gauge is defective.

Jim

 

[Slotts]

Ok, so what is next? I would try to work this backwards. Unhook the power feeds from your voltage limiter to just power the fuel gauge. What is the gauge showing all by itself?

Jim

 

[70SunFun]

I'm not up on the electrical stuff but last night I watched a couple of new Graveyard Carz episodes that I DVR'ed. On one of them Mark Worman received a brand new complete dash/gauges set up for a B5 Blue 1970 Challenger R/T in his shop. He put it on a test machine and he said something informative about why the new gauges peg 'full' like you mentioned. He went on to say that one can damage the gauges if one continues to test and does not fix the testing issue. See if you can retrieve that episode if you can DVR that show. Good luck!

 

[wigger]

Ok, so what is next? I would try to work this backwards. Unhook the power feeds from your voltage limiter to just power the fuel gauge. What is the gauge showing all by itself?

Jim

update to gauge problem, i have solved it. wire from gauge to sending unit must have been cut somewhere along the way. ran new from gauge to sending unit fuel gauge works fine and so do the rest of gauges, thanks Jim for responding, it took me down the right path.

 

[Slotts]

That is great news! That is what all of us Mopar folks want to see happen in the end. Another Mopar on the road, not on the side of the road.

Jim

 

[Steve340]

Jim I have a question if you don't mind.
Why did the fault in the fuel gauge affect all the gauges?