Aftermarket Gauge Problem?

[Black Sun 5.0]

Has anyone here ever experienced an electrical problem with their car that caused an aftermarket electrical gauge to give incorrect readings? I'm one of those people who always seem to post here about their 'overheating' problems and never seem to find a solution. I have a '91 Stang that started reading hot again this spring. I have an Auto Meter Phantom series temp gauge and on a warm day it will read 140* right when I start the car for the first time in the A.M. Yesterday, on the highway, it launched as high as 240* (it would have gone further if it could), but I didn't have any steam or boil over, at least that I could tell. At idle with my SN95 electric fan, the temp will drop pretty quick. Could something like a bad ground throw off the gauge and make it read out of range? Maybe a short?

 

[ECU5.0]

yeah, i believe a bad ground will make it read wrong

 

[HISSIN50]

also most senders provide ground, so if the sender wire is slightly chafed, it will read artificially high. you can check the resistance of the wire with a DMM.

since it starts off at 140, it is useless the way it is now.
good luck.

 

[HISSIN50]

im too lazy to edit. when i said chafed, i meant chafed and shorting out a smidge. also happens when the wires touch hot things and melt to them......

 

[hllon4whls]

It sounds like you already know you have a problem. I doubt that the air temp is 140 in NY, so It is not reading correctly. Get a mechanical gauge in that style. Then you wont have any more trouble. Or make sure that your dash is grounded to the block and that the block is grounded to the bat. I would remove the firewall strap ground, clean the crap out of the connection points and then put it back. Paint adds resistance that hinders ground reference. Scrape all that off and re attach. Then spray a little paint over the whole thing to make it pretty.

 

[Black Sun 5.0]

You know, I deal with 2 mechanics, one a regular Joe type the other a speed shop. Nobody wants to know anything about checking out all the grounds in the car. Personally, I'd like to have the whole damn car rewired, I don't even have interior or dash lights due to a blown fuse. Could the electrical issue 'kill' the unit's sender?

 

[BlackGT89]

Black Sun, if it's an electrical gauge trace the wire and make sure it hasn't gotten crimped or pinched somewhere. I had a wire get caught under the edge of a valve cover once and the gauge went through the roof !

 

[Black Sun 5.0]

OK, let me fill in the story a little more. This is the 3rd or 4th gauge this has happened with, not including the stock gauge.

 

[BlackGT89]

OK, let me fill in the story a little more. This is the 3rd or 4th gauge this has happened with, not including the stock gauge.

It was not a 5.0, it was my little 77 Merc. Capri V6. I had taken a valve cover off to adjust the valves. When I finished I put the valve cover back on and unknowingly trapped the wire to the temp sending unit under the valve cover. Next time I drove it the temp gauge went through the roof. It took me a while to figure it out, but when I traced the wire back, there it was, trapped under the valve cover ! When I removed it it all went back to normal.

 

[hllon4whls]

Black Sun, what do you want us to do? You need to help yourself here. If you cant fix that electrical problem that sounds as though it is affecting your gauge, put a mechanical gauge in there.

If you want to fix the whole, you are going to have to get someone that knows wiring.

 

[Nitrous N20]

A bad ground WILL case an erratic reading on the electrical guage. Make sure that it is grounded correctly first.

The next thing to check is the guage itself. Get the power and ground hooked up to the guage and then ground the sender. As soon as you turn on the power, the guage should go right to 0.

If it all works, try replacing the temp sender (unless you already have).

 

[hllon4whls]

A bad ground WILL case an erratic reading on the electrical guage. Make sure that it is grounded correctly first.

The next thing to check is the guage itself. Get the power and ground hooked up to the guage and then ground the sender. As soon as you turn on the power, the guage should go right to 0.

If it all works, try replacing the temp sender (unless you already have).

If you ground the sender, the gauge is going to go all the way to the hot/full/high.