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Fuel gauge and temp gauge gremlins

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charliecurrie
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Fuel gauge and temp gauge gremlins

Post #1 by charliecurrie » Thu May 28, 2020 8:31 pm

I've had this issue with my gauges since I've owned my car - about 8 years - and have not found a solution.

My gas gauge reads a quarter tank fuller than it actually is and the temp gauge reads about a quarter sweep lower than the actual temp.

Then, if I turn on the headlights or heater blower, the gas gauge will move about another quarter tank fuller and the temp gauge will move about a quarter sweep higher. If I turn both the headlights and the blower on, both gauges move even further.

I've tried a new constant voltage regulator - instrument cluster regulator - as well as a digital regulator to no avail. Also, made sure - as best I could - that the regulator was sufficiently grounded.

I've checked the voltage output at the sender end of the temp gauge wire and I get 5 volts. When I turn the lights on it jumps to 9 volts. And, a test light shows a pulsing voltage, like it should.

So, what do you think?

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Re: Fuel gauge and temp gauge gremlins

Post #2 by bubba22349 » Fri May 29, 2020 1:07 am

Think it reading a 1/4 fuller may have something to do with the fuel tank sending unit sometimes the float needs to be adjusted to read properly. It sounds like you getting a power back feed from the headlight switch to the gauge voltage regulator. Has the factory wiring harness been modded any under the dash? Good luck :nod:
A bad day Drag Racing is still better than a good day at work!

My Ex-Fleet of Sixes sadly these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

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Re: Fuel gauge and temp gauge gremlins

Post #3 by Cool23 » Fri May 29, 2020 8:05 pm

A bad earth connection to the guage cluster.
V8's are great but Six Inlines Just Fine. Cummins Advert.

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charliecurrie
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Re: Fuel gauge and temp gauge gremlins

Post #4 by charliecurrie » Fri May 29, 2020 8:44 pm

bubba22349 wrote:Thank reading a 1/4 fuller may have something to do with the fuel tank sending unit sometimes the float needs to be adjusted to read properly. It sounds like you getting a power back feed from the headlight switch to the gauge voltage regulator. Has the factory wiring harness been modded any under the dash? Good luck :nod:


I've considered the fuel tank sending unit, but that doesn't explain the temp gauge being off by about the same amount.

There was some monkeying with the wiring around the radio speaker, but no where else.

Not only the headlight switch - the heater blower switch, also.

It's only the two gauges controlled by the cvr that I have problems with, and like I said, I've changed it twice - one analog and a Scott Drake digital - no difference with either.

The cvr grounds to the cluster - I think I'll run a direct body ground to it. But, don't know why the lights and fan switch would effect the ground. Gremlins

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Re: Fuel gauge and temp gauge gremlins

Post #5 by bubba22349 » Sat May 30, 2020 12:05 am

X2 yes many times it comes down to a poor ground as one of the main causes of these odd electrical problems on these old cars, so sometimes you need more or better grounds in different locations. As to why turning on those two other switches will help I can only guess. And this is when they are turned to on it provides another grounding source to help. First thing I do with any new to me vechical is to clean every wire connection and ground from the battery posts back. Best of luck :thumbup: :nod:
A bad day Drag Racing is still better than a good day at work!

My Ex-Fleet of Sixes sadly these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

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Re: Fuel gauge and temp gauge gremlins

Post #6 by charliecurrie » Sat May 30, 2020 7:12 am

bubba22349 wrote:X2 yes many times it comes down to a poor ground as one of the main causes of these odd electrical problems on these old cars, so sometimes you need more or better grounds in different locations. As to why turning on those two other switches will help I can only guess. And this is when they are turned to on it provides another grounding source to help. First thing I do with any new to me vechical is to clean every wire connection and ground from the battery posts back. Best of luck :thumbup: :nod:


Thanks. I'll post back if/when I come up with a solution.i

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Re: Fuel gauge and temp gauge gremlins

Post #7 by Cool23 » Sat May 30, 2020 8:06 pm

Try running a new earth ground wire to the gauge cluster and see what that does for you. I have had the same issue myself.
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Re: Fuel gauge and temp gauge gremlins

Post #8 by Lazy JW » Sun May 31, 2020 8:59 am

Cool23 wrote:Try running a new earth ground wire to the gauge cluster and see what that does for you. I have had the same issue myself.


I too had to do this on my White Ox to cure my gauge gremlins
"The White OX" 1974 F-350 300-6, Stock single exhaust, Carter YF, T-18A, Dana70 w/4.11, Flatbed dually w/dump bed. "Where no oxen are, the crib is clean, but much increase is by the strength of the ox" (Proverbs 14:4)
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Re: Fuel gauge and temp gauge gremlins

Post #9 by B RON CO » Sun May 31, 2020 9:22 am

Hi, I agree that the problem could be the ground. After all, the cluster grounds to the dash and the dash grounds to the cowl. So somewhere it could be loose and corroded. But I am curious if you checked the voltage going into the IVR, and if it changes when you turn on the lights or heater. Good luck
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Re: Fuel gauge and temp gauge gremlins

Post #10 by Gene 64 2dr » Sun May 31, 2020 10:05 pm

You might want to also look at your light switch. I had a similar problem with my gas gauge and noticed a problem with the dimming of the dash lights and the voltage level would fluctuate when I went to dim the dash lights. My gas gauge never read full. I removed the light switch and cleaned the contacts on the pot and Sprayed contact cleaner in the switch housing. The pot in this case is an open style as it is not enclosed and was quite dirty. Try checking your 12 volt supply while trying to dim your dash lights or turning on or off your headlights. After a thorough cleaning my gas gauge read full and a dash lights Stopped flickering.
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Re: Fuel gauge and temp gauge gremlins

Post #11 by charliecurrie » Mon Jun 01, 2020 12:59 pm

B RON CO wrote:Hi, I agree that the problem could be the ground. After all, the cluster grounds to the dash and the dash grounds to the cowl. So somewhere it could be loose and corroded. But I am curious if you checked the voltage going into the IVR, and if it changes when you turn on the lights or heater. Good luck


Ive checked the voltage on the temp gauge wire at the sender and it does go up. If I remember correctly - it's been awhile - 5 amps with nothing on and 9 with the lights on.

No ground, the fuel gauge would read empty - weak ground, it would read less than actual - mine reads more than actual, i.e. 1/4 tank = empty.

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Re: Fuel gauge and temp gauge gremlins

Post #12 by charliecurrie » Mon Jun 01, 2020 1:06 pm

Gene 64 2dr wrote:You might want to also look at your light switch. I had a similar problem with my gas gauge and noticed a problem with the dimming of the dash lights and the voltage level would fluctuate when I went to dim the dash lights. My gas gauge never read full. I removed the light switch and cleaned the contacts on the pot and Sprayed contact cleaner in the switch housing. The pot in this case is an open style as it is not enclosed and was quite dirty. Try checking your 12 volt supply while trying to dim your dash lights or turning on or off your headlights. After a thorough cleaning my gas gauge read full and a dash lights Stopped flickering.


My fuel gauge reads greater than actual. Full tank and the needle is pegged all the way to the right - and, 1/4 tank = empty.

Turning the lights or heater fan on moves the needle to the right. Half tank reading with nothing on becomes 3/4 reading with the lights on - lights and heater fan on becomes full tank reading or more.

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Re: Fuel gauge and temp gauge gremlins

Post #13 by Lazy JW » Tue Jun 02, 2020 7:07 am

These gauges are dumb; they only move/react to the current flowing through them.

All of the circuits in question here are series-parallel Direct Current.

Poor connections/grounding can result in incorrect difference of voltage potential, causing undesired results.

It appears that the headlights and heater fan are drawing a percentage of their current through the ground path of the gauges (this is the series-parallel circuit mentioned above).

Electron flow being from negative to positive, the (partial) current flow will be from ground, through the gauges, then through the higher potential of the light (or heater) switch, and thence to the positive side of the battery.

Poor connections anywhere in the headlight or heater circuit could be the culprit.
"The White OX" 1974 F-350 300-6, Stock single exhaust, Carter YF, T-18A, Dana70 w/4.11, Flatbed dually w/dump bed. "Where no oxen are, the crib is clean, but much increase is by the strength of the ox" (Proverbs 14:4)
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Re: Fuel gauge and temp gauge gremlins

Post #14 by charliecurrie » Tue Jun 02, 2020 11:25 am

Lazy JW wrote:These gauges are dumb; they only move/react to the current flowing through them.

All of the circuits in question here are series-parallel Direct Current.

Poor connections/grounding can result in incorrect difference of voltage potential, causing undesired results.

It appears that the headlights and heater fan are drawing a percentage of their current through the ground path of the gauges (this is the series-parallel circuit mentioned above).

Electron flow being from negative to positive, the (partial) current flow will be from ground, through the gauges, then through the higher potential of the light (or heater) switch, and thence to the positive side of the battery.

Poor connections anywhere in the headlight or heater circuit could be the culprit.


Thank you. First response I've gotten that provides me with information I can use to track down my gremlins. Now, where do I begin? :wink:

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Re: Fuel gauge and temp gauge gremlins

Post #15 by Lazy JW » Wed Jun 03, 2020 8:53 am

Not knowing what vehicle you have, the very first thing I would do is to run a ground wire, 14 gauge or heavier, from the metal part of the dash, as close as practicable to the gauges, all the way to the grounding point of the battery.

Next, clean any connections in the heater circuit, all the way from the power source through the ground side. Then see if it makes any difference.
"The White OX" 1974 F-350 300-6, Stock single exhaust, Carter YF, T-18A, Dana70 w/4.11, Flatbed dually w/dump bed. "Where no oxen are, the crib is clean, but much increase is by the strength of the ox" (Proverbs 14:4)
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Re: Fuel gauge and temp gauge gremlins

Post #16 by charliecurrie » Wed Jun 03, 2020 10:18 am

Lazy JW wrote:Not knowing what vehicle you have, the very first thing I would do is to run a ground wire, 14 gauge or heavier, from the metal part of the dash, as close as practicable to the gauges, all the way to the grounding point of the battery.

Next, clean any connections in the heater circuit, all the way from the power source through the ground side. Then see if it makes any difference.


1966 Ford Falcon wagon.

Thanks once again for being so generous with your time and knowledge.

I actually don't believe the instrument cluster itself is grounded. I've had it out a few times. It's all plastic, and even though it's screwed into the metal dash, there obviously would not be any conductivity. The the cvr has a dedicated ground wire. And, the cluster lights are two wire - if I remember correctly, but I'll have to check that. The fan switch is located in the cluster also, and has it's own +/- circuit. As is the wiper / washer switches. Oddly, those two don't affect the gauges when turned on. The headlight switch is in the dash, not the cluster.

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Re: Fuel gauge and temp gauge gremlins

Post #17 by Lazy JW » Thu Jun 04, 2020 3:01 pm

After putting some thought to this, I believe I have been thinking about this issue backwards.

The IVR doesn't send out a constant voltage, it sends out a pulsing signal of approximately 12 volts. The instruments are electrically damped so as to not follow this pulsing too quickly.

The IVR works more like a turn signal flasher, using a bi-metallic strip with a heating wire wrapped around it. When the contacts are closed, there is a 12 volt output to the instruments, and when the strip gets hot enough, the contacts open, thereby dropping the output voltage to zero. The average output voltage will be around 5-6 volts.

If anything causes a reduction in current flow through the IVR, then the contacts will remain closed for a longer duration, thereby INCREASING the average voltage output. This will cause your gauges to read high. Turning on extra circuits will cause the voltage to drop at the input of the IVR, reducing current flow, etc.

First, make certain that the IVR is well-grounded.

Second, check out the connections in the fuse box (including the fuse itself).

Third (this is a long shot) check the radio suppression choke that is attached to the IVR. Maybe remove it entirely.

Good luck!
Joe
"The White OX" 1974 F-350 300-6, Stock single exhaust, Carter YF, T-18A, Dana70 w/4.11, Flatbed dually w/dump bed. "Where no oxen are, the crib is clean, but much increase is by the strength of the ox" (Proverbs 14:4)
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Re: Fuel gauge and temp gauge gremlins

Post #18 by charliecurrie » Thu Jun 04, 2020 4:12 pm

Lazy JW wrote:After putting some thought to this, I believe I have been thinking about this issue backwards.

The IVR doesn't send out a constant voltage, it sends out a pulsing signal of approximately 12 volts. The instruments are electrically damped so as to not follow this pulsing too quickly.

The IVR works more like a turn signal flasher, using a bi-metallic strip with a heating wire wrapped around it. When the contacts are closed, there is a 12 volt output to the instruments, and when the strip gets hot enough, the contacts open, thereby dropping the output voltage to zero. The average output voltage will be around 5-6 volts.

If anything causes a reduction in current flow through the IVR, then the contacts will remain closed for a longer duration, thereby INCREASING the average voltage output. This will cause your gauges to read high. Turning on extra circuits will cause the voltage to drop at the input of the IVR, reducing current flow, etc.

First, make certain that the IVR is well-grounded.

Second, check out the connections in the fuse box (including the fuse itself).

Third (this is a long shot) check the radio suppression choke that is attached to the IVR. Maybe remove it entirely.

Good luck!
Joe


This makes a lot of sense. When the lights are on, the voltage output of the cvr is around 9 volts - meaning the contacts in the cvr are in contact longer.

I was thinking backwards also. I knew the gauges were getting more voltage, not less, but I was confused on how that could be happening. The cvr is getting a weaker signal and consequently putting out more voltage. I know how and why the cvr works, but I don't think I would have ever come up with that solution.

I will check the fuse and grounds and see where that gets me.

Thanks,
Charlie

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Re: Fuel gauge and temp gauge gremlins

Post #19 by charliecurrie » Thu Jun 04, 2020 4:18 pm

"Third (this is a long shot) check the radio suppression choke that is attached to the IVR. Maybe remove it entirely."

I removed that, along with the voltage regulator, when I converter to a internally regulated alternator.

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Re: Fuel gauge and temp gauge gremlins

Post #20 by Lazy JW » Thu Jun 04, 2020 6:24 pm

I still believe it is a connectivity issue, but I now suspect it is on the power side rather than the ground side. Those old fuse boxes can get corroded inside where it is difficult to see. A sensitive (high quality) ohm meter can be helpful.
"The White OX" 1974 F-350 300-6, Stock single exhaust, Carter YF, T-18A, Dana70 w/4.11, Flatbed dually w/dump bed. "Where no oxen are, the crib is clean, but much increase is by the strength of the ox" (Proverbs 14:4)
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Re: Fuel gauge and temp gauge gremlins

Post #21 by charliecurrie » Thu Jun 04, 2020 11:45 pm

Got one.

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Re: Fuel gauge and temp gauge gremlins

Post #22 by Cool23 » Tue Jun 09, 2020 7:32 pm

Curious to know how you have got on with the problem.
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The link to my project on this forum http://fordsix.com/forum/viewtopic.php?t=41598

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Re: Fuel gauge and temp gauge gremlins

Post #23 by charliecurrie » Thu Jul 09, 2020 5:57 pm

Still no resolution.

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Re: Fuel gauge and temp gauge gremlins

Post #24 by Lazy JW » Fri Jul 10, 2020 8:05 am

Thanks for the update, it is nice to know that you didn't just wander off :D
"The White OX" 1974 F-350 300-6, Stock single exhaust, Carter YF, T-18A, Dana70 w/4.11, Flatbed dually w/dump bed. "Where no oxen are, the crib is clean, but much increase is by the strength of the ox" (Proverbs 14:4)
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Re: Fuel gauge and temp gauge gremlins

Post #25 by sixtseventwo4d » Tue Jul 14, 2020 9:43 pm

Get yourself what's called ground washers, these are washers with internal or external serrated edges. Where ever you locate a ground wire from your harness, be it on the firewall, kick panel, trunk , heck anywhere; unbolt it , brush/sand the eye terminal and grounding location. If you have more than one terminal at a location use these washers between each connection and at the bottom of the stack at the grounding location. These will help to bite into and keep a secure ground connection. Also apply a corrosion preventative to the connections and the surface. Your issue really sounds like a poor ground or deteriorated ground wire impeding current flow.
If you have a good DVOM you can locate your voltage drops across your circuits. By connecting in one circuit and turning the another on you may see an increase or decrease in range. if you ground your meter and use the pos meter lead to check your ground circuits it shouldnt reflect any voltage if it does you've found your problem. Best of luck.

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