The temperature gauge on my Fiero is inaccurate. At operating temperature it reads about 100 degrees, obviously inaccurate. So I tested the sensor, it was accurate. So I checked the wiring, no issues. Replaced the instrument panel (I just happened to have one lying down), same results. Hoping that someone had a similar issue and discover a solution, I’ve been stumped for three days.

-Trent

[This message has been edited by Trent_Illician (edited 07-11-2007).]

it's quite common for the gauge to read way low because when you turn the key to the CRANK position. the idiot lights go in to "bulb test" mode.
the circuit board in the instrument cluster has a design flaw that pegs the needle to the hot side. the needle hits a post and can eventually rotate more to the cool side of the scale or completely fall off.

quote Originally posted by buddycraigg: it's quite common for the gauge to read way low because when you turn the key to the CRANK position. the idiot lights go in to "bulb test" mode. the circuit board in the instrument cluster has a design flaw that pegs the needle to the hot side. the needle hits a post and can eventually rotate more to the cool side of the scale or completely fall off.

Ya, I had read that somewhere just after I got the car, however, I did replace the instrument panels. So unless they both had the same problem, and to the same degree to boot, that isn’t the problem. In addition, the car only has 90,000 miles, if I remember correctly, that usually starts becoming an issue around 150,000-200,000 miles. Any other ideas???

The "Pegging Temperature Gauge" was a factory defect in EVERY Fiero with a temp gauge. Instead of the power being applied to the overheat bulb during the bulb test when you start the car, it is applied to the gauge itself. The needle pegs off the high side each and every time the car is started. Over time this tends to knock the needle loose and make it read low or fall off or stick past the overheat range. Its an easy cut and splice to fix it though.

[This message has been edited by Hudini (edited 07-10-2007).]

Maybe I didn’t explain myself throughly. I replaced the temperature gauge as part of the instrument panel. So, the gauge can’t be the issue.

quote Originally posted by Trent_Illician: Maybe I didn’t explain myself throughly. I replaced the temperature gauge as part of the instrument panel. So, the gauge can’t be the issue.

maybe i didn't explain myself throughly.

it would not be uncommon to have 2 defective temp gauges because they ALL had this problem.
unless you have see the second temp gauge read correctly in another car, then you cant assume that it is accurate.

[This message has been edited by buddycraigg (edited 07-11-2007).]

Exactly as buddycraigg said, EVERY car had the problem so each and every gauge is suspect unless you calibrate it AND fix the pegging from happening again. It does no good to move the needle to the most perfect spot only to have it move the next time you start the car.

What to do? Perform the "Pegging Temp Gauge" fix first. Then calibrate the needle using a known good source such as the ECM temp sensor or a mechanical gauge. The ECM temp sensor can be read with a laptop (preferably an old one with a serial port), Winaldl software (free download and use), and a ALDL cable. The ALDL cable can be made for less than $10 in parts or purchased from the mall here from a member or online from aldlcable.com.
Build it: http://couleefiero.tripod.com/ALDL.htm
Winaldl software: http://winaldl.joby.se/

Okies, I suppose I didn’t really consider the possibility that both instrument panels could be bad, do a comparison with mt dads Fiero and I’ll get back to you.

quote Originally posted by Hudini: The ECM temp sensor can be read with a laptop (preferably an old one with a serial port), Winaldl software (free download and use), and a ALDL cable.

What OS requirements for the laptop? just some version of Windows with a serial port?

The WINaldl software is getting a bit long in the tooth. I think it was made for Win98. It does work with Win XP though. I used an old PII 266mhz laptop with a serial port and it worked like a champ.

The serial port is not an absolute requirement, it just removes the issue with USB ports sometimes not working correctly. The aldlcable.com website explains it better. Apparently there are only one or 2 USB adapters that work correctly. Maybe Win Vista will get rid of the issues? lol

the connector for the temp guage sesnor is also a problem. the hard plastic get pretty brittle - might just be a contact problem.

and, if you tested the sensor - did you test the signal/voltage the guage is getting?
and - didja test the right sensor? there are 2 temp sensors after all....

Okay, according to the factory service manual, temperature sensor works off resistance. 55 ohms is supposed to read 260 degrees, and 1365 ohms reads 100 degrees. So I took a wide range of resistors, and connected then directly to the wiring and plotted a graph. I then took the same resistors and plotted a graph on my fathers Fiero (who’s temperature gauge works). The resulting graphs were almost identical.

The only other thing of interest was that it appeared to read 100 degrees at 550 ohms instead of 1365 ohms... a mistake in the book maybe???

Prythian: As for the connector to the temperature gauge. Honestly I like that as the issue too, however, I tested it for resistance also, and it came up clean. Somehow it still seems to make sense to me, but I just don’t know how else it could be bad.
As for the signal/voltage to the gauge itself, I didn’t check that. All the other gauges work just fine, however, if you still think that could be the issue, I will check that out.

On a side note. I want to apologize if I came off as an ass earlier. This problem has been taunting me for nearly a week, and I’m a little on the frustrated side.

-Trent

You are alright. You seem to have a good head on your shoulders and want to get it fixed. You will, don't worry. Its just a matter of elimination. Try this, put the correct resister in to make it read 100. Then take the gauge out and pull the needle off. Now reposition it to read 100 degrees. Now check the resistance for 260 degrees. Does it read correctly? If so you have a calibrated gauge. If not it is probably a bad gauge. I bought Rodney Dickmans Temperature Gauge Test Leads to check my gauge. The gauge absolutely pegged off the scale when it should have read 260. No matter how much I adjusted the needle it would peg. I replaced the gauge and everything is now good.

quote Originally posted by Hudini: The WINaldl software is getting a bit long in the tooth.

Can you clarify? What is "long in the tooth"?

Its been around awhile, thats all. I'm not sure if the authors will continue to update it to run with the ever updating Windows. I mean, it is free. They are giving us a program they worked hard on and asking for donations only. I sent them some money because I really liked it. It does work now and is very useful which I guess is all that matters. Unlike Win98 SE where MS stopped supporting it.

I checked my laptop form work. It has a serial port . I read some other post that someone here on Pennocks makes these cables. Is this still true?

srat110 made them at one time. Not sure now.

Its really easy to build though. $10 in parts and a solder gun and solder. Mine worked first time (surprised me). Some folks here make some really super nice ones for themselves. Not sure if you could talk them into making one for you for the right price.

quote Originally posted by Hudini: srat110 made them at one time. Not sure now. Its really easy to build though. $10 in parts and a solder gun and solder. Mine worked first time (surprised me). Some folks here make some really super nice ones for themselves. Not sure if you could talk them into making one for you for the right price.

I took a look at one of the links above. You are right, they do look easy to make. The only part missing in the cable build link is the male ALDL connector. This cable build just instructs you to stick the wires in the appropriate sockets of the female connector on the car. Do you know where to buy the correct male portion?

quote Originally posted by sjmaye: Can you clarify? What is "long in the tooth"?

From the randomhouse word of the day web site...

Long in the tooth means 'elderly; old', and by extension 'past one's prime; over the hill'.

The expression derives from horses, of all things. As horses age, their gums recess, which is the origin of the practice of examining a horse's teeth to determine its age (and therefore value), a sort of early version of kicking the tires. (Horse traders, like used-car salesman, are not to be trusted.) An old horse's gums will have recessed so much that the roots of the teeth are visible, thus making the teeth appear longer--hence long in the tooth to mean 'old', and hence used figuratively paralleling figurative senses of 'old' such as 'past one's prime'.

Long in the tooth is first found in England in the nineteenth century, though it's likely that it was in use much earlier but never got recorded.

quote Originally posted by sjmaye: I took a look at one of the links above. You are right, they do look easy to make. The only part missing in the cable build link is the male ALDL connector. This cable build just instructs you to stick the wires in the appropriate sockets of the female connector on the car. Do you know where to buy the correct male portion?

Here are some ideas on what you can do. Dodgerunner has a unique setup for his. Jazzman has probably the most elaborate I've seen.
https://www.fiero.nl/forum/A...060811-2-069730.html