So Thursday I jump in the truck and get on the highway, and, as I,(and I guess most of you) always do when getting on the interstate, watch the pyro out of the corner of my eye. Well, something is wrong, as it pegged itself THE OTHER WAY. Instead of going clockwise, it went counterclockwise past zero, and now it sits there. The strange thing is that when the truck is off, the gauge reads 0 as it should. I'm headed out to tear into the truck, checking all the power connections and sender. My tranny gauge has really never moved since I put it in either, except at higher than 1/2 throttle angles. I've always attributed that to great cooling. Thanks in advance for any other advice on troubleshooting. It's an Autometer Z-Series in a 3 gauge pillar with the sender pre-turbo.....

Kevin

 

sounds like something got hot under the hood and fried wiring.

 

...so since I'm under the truck anyway, I decide to pull the sender for the tranny gauge as well. It came out in pieces. I'm guessing senders for all gauges regardless of mfg are pretty much the same across the board. Solid brass with a post and a nut to attach a wire running to the gauge. Well, when I removed the sender, a black sleeve and a copper spring looking thing were still in the tranny port. Comparing the current sender to a new one,(I happen to have a second new tranny gauge), there is still the outer brass piece still it the port. Any ideas?

All wiring and connections are sound and test good for continuity. So either the gauge(s) are bad or the senders, I think......

Does the tranny gauge sender ground through the tranny itself? The 1 wire hookup has me thinking......

 

So everything checks ok, voltage to the gauges is good, both loaded on no load, running and off. I'm puzzled. I guess a bad gauge or sender. If anyone has input, please let me know.

Kevin

 

Isn't the pyro a thermocouple? Sounds like it went bad. Or the wires opened up somewhere.

 

What voltage do you read at the gauge?

 

Thanks for the response gents. Here's any info I have and some pics(albeit bad ones) to assist you...

At idle -

Voltage across pyro sender leads at gauge - .06V

Resistance across pyro sender leads at gauge - Started at 73k ohms after 30 seconds it had climbed to 86k ohms

Voltage across across drivers side battery terminals - 13.86V

Voltage across pyro gauge power (red/black hardwired) leads - 13.70V

Voltage across gauge light leads is unnecessary I think!

The gauge will sometimes read properly for a few seconds, then quickly fall back to this:

Truck Running, gauge looks like this


Truck Off



Weird. Should I measure resistance across the sender disconnected from the gauge? Will this number help anyone?

Thanks again for any & all feedback. Calling Autometer tomorrow as well.....

-Kevin-

 

Disconnect the input leads and bridge the terminals with copper wire. Then connect another copper lead from the (-) input side to ground. With the gauge shorted in this manner it should give an ambient temperature indication.

Also, on the output voltage, you should be testing with the DVOM set to mV if you have it. Establish a baseline at idle and continue to monitor as you apply more heat. The mV readings should increase in a reasonably linear fashion.

 

Pardon my ignorance, when you say input leads, are you speaking of the gauge power leads or the sender leads. I'm assuming the power leads. But will the gauge operate without power? Or am I testing the sender unattached to the gauge? Sorry to be a PTA, just clairifying.....

 

I had a similar experience with my autometer pyro, evey once in a while it would go crazy. I had used a common ground for the pyro and a few other things,and once I moved the pyro ground to a seperate ground by itself it acted normally again. I have no idea why this fixed it but thought I would pass it along.

 

Sorry....lost track of this thread. I've gotta bad case of CRS this week.

The input leads are the yellow jacketed leads from the thermocouple. Remove those leads from the gauge and create your short across the posts on the gauge where the input leads were. With no other changes to the gauge or wiring creating this short will make the gauge read ambient temperature if the gauge is working.

Since the input leads are disconnected from the gauge you put your DVOM on the leads and apply heat to the thermocouple and watch for an increase in the mV output from the thermocouple.

One of those tests most likely will not work....that would be the source of your gauge demon.

 

Just got back from two weeks in Spain, thought I would do my tests as Scott had described...

Disconnected sender leads from the gauge terminals. Shorted the pyro sender terminal leads at the gauge, and as promised the gauge read between 50-100 degress F. Turned key to ON. Gauge held steady.

Pulled the sender from the manifold, hooked up the sender to my DMM, set at mV, read 31mV. grabbed a lighter and ran the sender tip across the flame. slowly the number climbed to roughly 65mV. Take the flame away, and the number dropped, as expected. Repeated as few times, just 'cause. Not really getting the answers I wanted.....Bummer.

Put the sender back in the manifold. Left the sender terminals shorted on the gauge and left the sender leads disconnected from the gauge and hooked up to the meter. Sender read 6.1mV, really low compared to my first reading. Fired up the truck, gave it a few throttle blasts, as this seemed to be where the gauge would go nuts. Gauge held steady, sender climbed to 34mV. Took it for a drive with the DMM hooked to sender. Some of the readings made sense others didn't. Steady 1/4 accel the readings climbed and fell as I thought they should, but when I really mashed the pedal, the readings would fall to 10mV bounce up to 50mV, instantly dropto 22mV back up to 40mV, all during an acceleration run. Technically, EGT's should be steadily rising at that time, causing the output of the sender to do the same. Bad sender, I would think. But I also wanted to run my findings past Scott(as it's his troubleshooting flow chart that I used) and anyone else whom might have input. Thanks everyone for the help, gonna call Autometer today and try to get a replacement sender sent out N/C as the gauge is under a year old.

Kevin