Autometer Pyro Gauge doesn't go to zero when off, normal/bad?????

[BK]

Hi folks,

After buying them many many months ago, just when the weather got cold, now that it's warm I finally installed my gauges.



Bought Autometers from Genos.



All seems fine, but the pyro gauge doesn't go to zero when I shut the truck off.



I have the gauge powered from an circuit that's only on when the truck is on.



Is this normal for the Autometer gauges?

My friends VDO pyro gauge goes to zero when the truck is shut off.

I would have expect that same.

Bad gauge, or normal for an autometer pyro gauge?



Thanks,

B0b

 

[WMonroe]

I never thought about it before but mine does the same thing. It does go to zero after the truck has sat all night and then I turn the key on.

Will

 

[BK]

I guess I'll find out tommorrow morning.

It seems it maybe holding the last reading. That was my buddy's guess. Went over to show him the gauges after I finished. He cycled the ignition switch and it went down from 400 to 200.

 

[LOtero]

hmmm my pyro seems to be working fine, but when i turn the truck off, it just goes to wherever, be it 1500, or like at the 6 o'clock position, now your post got me thinking about this. its very inconsistant, but when i turn the key on, it goes to normal temps, is this because its not powered by a constant hot?

 

[dhill]

I have the autometer gauges in my truck. In the instruction sheet it says that there is a re-zero circut that has to be allowed to run before you start the truck. That takes about 1-1/2 seconds in my truck. I don't always let the heater run its cycle when the engine is warm. But after I read that, I watch the gauges go to zero and back again before I start. Usually by then the heater light is out anyway.



Dave

 

[BK]

After sitting all night, while letting the heaters cycle this morning, that guage did go to zero. It seems it's hold the last measurement when it's turned off.

RTFM, uhm, missed that one, I guess I didn't read the sheets close enough.

 

[gonehuntingagain]

You guys all make my gauge look like it is the oddball. When I shut off the key, the gauge snaps down to zero, and when cold and I turn the key on, it just barely comes off of zero.

I installed the Autometer gauges just a few weeks ago. I have the Z series with the street probe if that makes any difference.

 

[LOtero]

You guys all make my gauge look like it is the oddball. When I shut off the key, the gauge snaps down to zero, and when cold and I turn the key on, it just barely comes off of zero.

I installed the Autometer gauges just a few weeks ago. I have the Z series with the street probe if that makes any difference.

Thats what i want mine to do, what do you have your guage wired into? a constant hot i assume?

 

[BK]

I have the Z series as well.

They shouldn't be wired constant hot. Should be on an a switched ckt. The only reason I see to switch it's power, is to save battery drain. If powered all the time, and the truck is turned off, it will just keep reading the temp as it cools down.



Went out during lunch and the meter was still on 400, which is where it was after the drive in and idling in my parking spot for a few.

Turned on the key and it went down to aboutg 100 or so...

So it's holding the last readings and taking a new reading when turned on.

This morning it went to Zero after sitting all night.



Bought mine 10/2004, but got too cold to quick, so finally installed them this weekend.

My buddy's VDO's goes down to zero when he turns off the truck.

 

[AggieJustin]

You guys all make my gauge look like it is the oddball. When I shut off the key, the gauge snaps down to zero, and when cold and I turn the key on, it just barely comes off of zero.

I installed the Autometer gauges just a few weeks ago. I have the Z series with the street probe if that makes any difference.

If you've got an oddball, so do I. My gauge drops to 0 when turned off. Powered from a key-on circuit in the fuse box. Also goes to 0 during the start cycle, just like all the other electronics.



JM

 

[DJamrose]

i had auto meter gauges also but think about it if it's 70 degrees outside why would it got o zero when the manifold is 70 degrees the only time mine zeroed out was in winter when temps dropped below zero degrees just my 2 cents

 

[BK]

Your right, I didn't look all that close, there's a hatched out area around zero.

That's why it didn't drop to complete zero at lunch.

But this morning when it looked like it did, it was 45degs this morning.

 

[LOtero]

hmm any ideas why mine just goes wherever it feels like it when i turn off the key?

 

[lil red cummins]

i think there is some confusion about how some of these pyro gauges work. if you have ONLY the 2 wire thermocouple, that makes it operate, there is no on or off difference. it is ON all the time. it is the millivolt output generated by the pyro probe itself that makes it operate. you will also have wiring for the lights but that does not operate the gauge. my di-pricol is of this design.



if you DO have seperate power connections besides the thermocouple wire, (again not the light wiring) then you have the type that has what is called a thermocouple reference. this type of unit would allow the needle to drop or even float once power is removed. in my industry, this type is not as accurate after immediate power up. the "reference" needs to heat up and stabilize before reading accurately. however, this is when i am resolving tenths of one degree. this is not an issue on the trucks since we are looking at maybe 25 degrees at best resolution.



hope this helps.



jim

 

[BK]

hmm any ideas why mine just goes wherever it feels like it when i turn off the key?

Mine seems to be holding the last measurement after the key is turned off, and goes to the new temp once turned on.



I have no idea why it even holds the last temp. I would assume since the gauge needs the applied power to make a measurement, that once the power is removed it would just to go zero.



The Autometer has a separate 12Vdc +/- that needs to be applied for the meter to work, ( there are separate wires for the light)



lil red, do you know if a thermo ref meter has it's movement driven by an amplifier? If so, once power is removed, it just seem strange that it would even hold it's last reading, never mind go anywhere it wants after having it's power removed. And I know it's not that thermo couple doing it. Because after I installed the probe in the exhaust manifold, I tested the meter, hooked it all up under the hood, fired the truck up, saw the temps go up. Shut the truck down, removed 12Vdc from the meter and detached the thermo probe, and it held it's last reading (400DegF) ALL Day until permanently installed later that night. When it was powered up again, the meter took a new measurement and went down to just below 100. Even taping the meter lightly doesn't cause the movement to float down. Maybe the movement is damped and held in place by some friction with no return force?

If the damping was lighter and the friction was lighter... maybe that's why LOtero sees his jump? just thinking while typing... ... never did movement design. . so have no idea.

 

[Bertram65]

Mine used to go to 0 when I turned the key off, then after about 5 months it went to 6 o'clock when I turned the truck off. Called Autometer they said it was normal, if left overnight it goes to zero when power is applied again, if I then take the key out without starting it stays at 0, very strange but the readings have not changed to I guess it is ok.

 

[lil red cummins]

its not really an amplifier as you might think. its more about creating a very small magnetic field on a coil, and there may be as many as four of these coils around the meter movement. the needle part is normally attached to a permanent magnet and will be "moved" based on where the coils drive it. the difference between the reference voltage produced and the thermocouple voltage produced are applied to the different coils in a push/pull relationship and that actually moves the North/South pole relationship and therefore rotates the needle.



the reason the needle does not move once the power is removed is for two reasons. once the power is removed from the coils, there is still some residual magnetism in the coils and the polarity at which they were turned off stays the same. secondly, this factor is somewhat responsible for the damping or freezing type action of the needle, because the magnet is happy where it is and is unlikely to change without new input from the coils.



I am explaining this as best i can. if anyone else with knowledge on this subject can be more precise, please chime in.



suffice it to say, there is probably nothing wrong with you gauge if it stays in place after shuting off the ignition. and yes it will move to the new temp once the ignition is turned back on.



by the way, DO NOT try to "play" with the meter by waving a magnet around the front of the gauge. this could affect the calibration and could render the gauge useless for a while.



they will normally get back to normal after 1-2 weeks, but i wouldn't chance it.



ps



- this whole operational scenario is based on the gauges i have worked on. i could be way off base on the precise operation of your gauges. obviously the best source for technical operation on these gauges would be with the manufacturer. (that's my all purpose disclaimer)



jim

 

[BK]

thanks lil red, makes sense.

I used to do control ckts and power conversion. never did movements.

How you explain it makes perfect sense.

 

[gonehuntingagain]

Thats what i want mine to do, what do you have your guage wired into? a constant hot i assume?

I have it wired into the "spare" outlet in the fuse panel in the dash. It goes dead when the key is turned off. The ground is connected to the frame rail that runs along the bottom of the dash just below the steering column.

Maybe your ground is part of the issue - like my FP gauge - it reads higher when the lights are on.

 

[BK]

The pyro is a two leaded device, so the signal is making it straight to the guage and shouldnt be effected by grounding issues.



The fuel guage, while it looks like you can run one ground, you shouldnt.

There should be a "return" wire from the negative of the sensor that is brought up with the signal wire to the gauge so the local ground for the lighting wont cause that reading change. I see a lot of installations where the negative of the fuel pressure sending is grounded where the sending unit is and then a ground is picked up local to the gauge.



Same to make a temp sender more accurate. We all run one wire from the temp sensor to the gauge and pickup ground under the dash. But if you look at their instructions more closely, they call for an "engine" ground... meaning picking up the ground or the negative for the gauge as close as possible to where the temp sensor is. The voltage drop along the path that the ground current flow between the temp sensor and where you picked up the ground under the dash for the gauge can be littered with many 10's - 100's MilliVolts of drop and noise that will effect the gauge reading.