Having some issues with my temp gauge (I did do a search!). It's peged far left, dosen't really do anything. Also, there isn't any temp light that is lit on the dash anytime. I took off the wires on the temp sending unit and grounded them together (I read somewhere that this should set the light off at a minimun) and I get nothing.
So, I guess my questions are:
Does the temp warning light illuminate when the ignition is first turned on? (Where is it at? Is it with the other lights, or near the guage?
Where should I start?
Will touching the two wires on the temp sending unit really illuminate the light? What's a good check procedure to see if the gauge is really working?
You're suppose to ground the wires. One is the gauge, the other is the light. The gauge should peg all the way to the right when grounded, and the light, of course, will turn on when its wire is grounded. I can't remember if the key needs to be on or not.
Ok, so I grounded the wires and verifed the light as well as the gauge works. Replaced the sending unit, did the temp guage fix. The light works as well as the gauge (somewhat).
What the gauge does is sweeps slowly over to the red marks. It does this about 2-3 minutes after starting it. I read through alot of posts and I thought I saw some fix on it, but couldn't seem to find it again. Any thoughts? The sending unit is new and the car was pretty cool when I started it, the needle just makes a slow sweep into the red position.
I am having the EXACT same problem with my vehicle as well. 2-3 minutes and its over by the 240-250 mark. I verfied my guage and light as well. I have replaced the sending unit twice now yet no fix. If you find it let me know!!! I will continue to search as well.
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10:25 PM
85pontiac Member
Posts: 196 From: Elderton, PA Registered: Feb 2005
And this is the exact same problem I'm having with my 87 GT. I've also replaced the sending unit twice, and I've the entire instrument cluster apart and cleaned every single contact in the I/C. I tested the gauge with different values of resistors, and the gauge functions properly. But hook the wires up to the sending unit, turn the key on (the engine doesn't even have to be running) and after about 1.5 minutes, the gauge starts to creep, until it's completely pegged on the far right side.
I've asked before, people try to help, but then it seems to get forgotten and the threads are dead. Maybe this time someone will find an answer.
------------------ 1984 Sport Coupe Auto., 130,~~~ miles, bad duke 1985 Sport Coupe 5 Speed, 55,000 original miles 1987 GT Auto., 154,000 miles, partial daily driver 2006 Jeep Wrangler Rubicon, 5" lift, 35" tires, partial daily driver 1983 Yamaha Midnight Virago 920 1975 Cadillac Coupe DeVille, 25,000 original miles 1963 Buick Electra 225 1936 Dodge Two-door Touring Sedan
No, if I use a resistor, the gauge reads normally, where it should with whatever value resistor I have connected. If I hook it up, then it sweeps. I've added an extra ground between the engine and body. And I've also tried using a jumper wire with alligator clips connected to the battery's ground and the sending unit's body. Still the same. I would try another gauge, but I don't have one to try out. I have two other cars, but I don't feel like tearing they apart, as one is my show car, and the other is sitting at a storage lot and is currently infested with bee's nests, and I absolutely loathe bees.
------------------ 1984 Sport Coupe Auto., 130,~~~ miles, bad duke 1985 Sport Coupe 5 Speed, 55,000 original miles 1987 GT Auto., 154,000 miles, partial daily driver 2006 Jeep Wrangler Rubicon, 5" lift, 35" tires, partial daily driver 1983 Yamaha Midnight Virago 920 1975 Cadillac Coupe DeVille, 25,000 original miles 1963 Buick Electra 225 1936 Dodge Two-door Touring Sedan
Well if it holds with a resistor in place of the sender then I think the gauge is ok. So do you connect the resistor to the sensor plug a t the engine. If so then that would say the wires are ok also.
If the gauge keeps increasing that would seem to mean it's seeing a lowing resistance. I've seem semicondutors devices do that when they heat up but can't see how a temp sender would do that.
The only way I could see that happen is if the thermistor was getting heated by the voltage from the gauge. It should not be enough current to do that unless the gauge was faulty.
Going with that idea you could do a test between two Fieros if you have another that does not have the problem. You could measure the current flow thru the sender on a working and non working car to see if they where the same.
Has the pegging fix ever been done on the car? By you or a prev owner? I could see if it was miss wired and the temp lamp was in the gauge circuit the lamp would increase the current to the thermistor and might cause the problem. You could test that idea by removing the temp lamp from the dash and see if the problem goes away.
I'm just spit balling ideas here..
[This message has been edited by Dodgerunner (edited 05-18-2008).]
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06:41 PM
85pontiac Member
Posts: 196 From: Elderton, PA Registered: Feb 2005
No, the pegging fix has never been done. As for the light, I've tried switching the pins on the SU, and, just like the gauge, the light will stay out for a couple minutes, then the light itself will come on very dim, then get progressively brighter.
I'm thinking that there must be a problem in the wiring. The next thing I'm going to try, when I get time, is to run a new wire from the sending unit straight up to the back of the gauge. If this fixes it, then I will route the new wire accordingly and be done with it.
If that doesn't work, I'm buying an aftermarket temp. gauge and I'll really be done with it.
There you go, just what I was trying to explain above. My guess is someone in the past tried to do the pegging fix and did not do it correctly. Or was just wired differently from the factory which was already wired incorrectly.
Your temp light is wired in parallel with your gauge which increases the current running through the temp sender.
What you descibe is just what would happen. The extra current flow caused by the lamp going through the sender causes a heating effect to the thermister. As the thermister heats up its resistance decreases just as it should. The decreased resistance causes the current to increase which in turn causes the thermister to to heat up even faster. Also as the current increases the light would become brighter and your gauge would swing to full hot.
As I said, a very easy test would be to pull the temp light blub out and I bet your temp gauge would then work just fine. You could then figure out the wiring if you want.
[This message has been edited by Dodgerunner (edited 05-18-2008).]
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10:13 PM
PFF
System Bot
Mister Member
Posts: 1975 From: Calgary, Alberta, Canada Registered: Aug 2004
Did the peg fix properly. Replaced new sender unit, it produces resistance according to chart. Gauge works well with resistors. Light and gauge responds correctly to grounding.
But...After the engine warms a bit the gauge will peg to the left (minimum)... ???
[This message has been edited by Mister (edited 05-18-2008).]
Did the peg fix properly. Replaced new sender unit, it produces resistance according to chart. Gauge works well with resistors. Light and gauge responds correctly to grounding.
But...After the engine warms a bit the gauge will peg to the left (minimum)... ???
From your discription sound like something is becoming open when it heats up. When you check the resistance of the new sender did you check it when it has quit working and the engine is hot?
Did the test with the resistors when it is hot and not working?
Did it start doing this after you did the pegging fix?
You might also try unplugging the dash connector on the left side and reconnecting it. The ground for the gauge as well as the sender signal comes thru it and if it might be intermitant as the dash heats up a little.
[This message has been edited by Dodgerunner (edited 05-18-2008).]
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11:10 PM
May 19th, 2008
85pontiac Member
Posts: 196 From: Elderton, PA Registered: Feb 2005
There you go, just what I was trying to explain above. My guess is someone in the past tried to do the pegging fix and did not do it correctly. Or was just wired differently from the factory which was already wired incorrectly.
Your temp light is wired in parallel with your gauge which increases the current running through the temp sender.
What you descibe is just what would happen. The extra current flow caused by the lamp going through the sender causes a heating effect to the thermister. As the thermister heats up its resistance decreases just as it should. The decreased resistance causes the current to increase which in turn causes the thermister to to heat up even faster. Also as the current increases the light would become brighter and your gauge would swing to full hot.
As I said, a very easy test would be to pull the temp light blub out and I bet your temp gauge would then work just fine. You could then figure out the wiring if you want.
Does it make any difference if I tried all of this with the light's wire unplugged from the sending unit? Because the light's been unplugged all the times I've tested things. Also, the light functions properly. But does any of that make a difference to what you said above?
Not really, the wires are most likely cross connected up in the dash area so having it disconnected in the rear would not make a difference. The light and gauge would still be connected together up front.
Pull the temp bulb out, I'd be very surprised if that does not corrent the gauge at least.
[This message has been edited by Dodgerunner (edited 05-19-2008).]
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02:29 PM
85pontiac Member
Posts: 196 From: Elderton, PA Registered: Feb 2005
Originally posted by Dodgerunner: Did the test with the resistors when it is hot and not working? Did it start doing this after you did the pegging fix? You might also try unplugging the dash connector on the left side and reconnecting it. The ground for the gauge as well as the sender signal comes thru it and if it might be intermitant as the dash heats up a little.
Thanks Dodgerunner,
- After peg fix it was fine.
I ran another test today with the engine hot and idling. - According to the Ohm meter - Sender is O.K when the needle dips left - I've cleaned the reconnected all dash connectors It tested fine idling (from warm) for a couple of minutes but I'll do a test drive tomorrow and report. If it fails again I'll try removing the temp light bulb.
Originally posted by Mister: I ran another test today with the engine hot and idling. - According to the Ohm meter - Sender is O.K when the needle dips left - I've cleaned the reconnected all dash connectors It tested fine idling (from warm) for a couple of minutes but I'll do a test drive tomorrow and report. If it fails again I'll try removing the temp light bulb.
Mine failed after 8 minutes of the test drive next comes out the bulb.
I'll try it soon, I haven't had time to touch the car yet. I work two full time jobs (about 68 hrs. a week) and usually by the time I get home I just flop into bed. But I have Mon. off so I'll probably try it then.
I'll be sure to let you know what I find though!!!!
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03:28 PM
PFF
System Bot
May 29th, 2008
85pontiac Member
Posts: 196 From: Elderton, PA Registered: Feb 2005
Well, Dodgerunner, I pulled the bulb out today and still no difference. It definately has to do with heat/resistance, because it was fairly warm here today, and the car sat outside in the sun all afternoon till I got to it. When I turned the key on, almost immediately the gauge started to rise, it normally would take about a minute for it to start moving.
Darn! rain on my parade!.... Almost sound like it has to be the gauge then, unless some other type of load is still wired in with the sensor...
Next Idea would be to either try another gauge, or unplug the sensor wires at the sender and then unplug the dash plug on the left (door) side of the dash and measure the plug pin that goes to the sensor. It's pin 11. Here is the pic of the plug side of the dash so you will know which pin on the plug it is... Should be a light green wire. Or guess you could just unplug all and read at the sensor pin. (duh!)
With everything unplugged you should not read anything to ground on the wire with the key switch in the off position. If you do then there is still something loading the circuit. If not then it might be the gauge... Although if it does not do it with a resistor sub'd for the sensor then it would still seem to be something on the wire circuit and not the gauge.
[This message has been edited by Dodgerunner (edited 05-29-2008).]
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02:42 PM
May 30th, 2008
85pontiac Member
Posts: 196 From: Elderton, PA Registered: Feb 2005
Okay. Don't know how many days it will be before I actually get around to working on it again, but I'll definately try that. I've actually been meaning to check the wires for a long time (since I discovered the problem) but I just never got around to it. I tried to get the car inspected yesterday so I can actually drive it again (expired in April) and it FAILED for the parking brake not holding enough. This is the first time in my life that I have ever had anyone actually check the parking brake. And I took it to this guy because I knew he was too old and deaf to hear my exhaust leak.
------------------ Adam 1984 Sport Coupe Auto., 130,~~~ miles, bad duke 1985 Sport Coupe 5 Speed, 55,000 original miles 1987 GT Auto., 154,000 miles, partial daily driver 2006 Jeep Wrangler Rubicon, 5" lift, 35" tires, partial daily driver 1983 Yamaha Midnight Virago 920 1975 Cadillac Coupe DeVille, 25,000 original miles 1963 Buick Electra 225 1936 Dodge Two-door Touring Sedan
