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Diagnose Instrument Panel / Cluster Problems by OziDarklighter
Started on: 04-28-2014 07:43 PM
Replies: 5 (423 views)
Last post by: 84fiero123 on 04-30-2014 08:53 AM
OziDarklighter
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From: Belleville, MI, USA
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Report this Post04-28-2014 07:43 PM Click Here to See the Profile for OziDarklighterClick Here to Email OziDarklighterSend a Private Message to OziDarklighterEdit/Delete MessageReply w/QuoteDirect Link to This Post
I just bought an 85 SE in beautiful condition. The problems I inherited are in the instrument panel/cluster which I don't know much about:

-- Fuel Gauge - Occasionally works, currently shows 'uber-full' all the way to the right.
-- Speedometer - Bounces around +/- 10mph, but doesn't get above 30mph regardless of speed.
-- Tachometer - Works great!
-- Oil Pressure - All the way to the right off the gauge.
-- Temperature - All the way to the left off the gauge.

I've replaced (and verified) all fuses are correct. I've searched on these problems, and it doesn't seem like the 'pegging' problem, since nothing spikes up really high.

My question is... Where do I start?
Should I be looking to replace the instrument panel from a parts car? Track down wiring? Does anyone know a comprehensive source for wiring info on the cluster? I'm trying to get an idea what I'm getting myself into :-)

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-Ozi

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phonedawgz
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Report this Post04-28-2014 09:09 PM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
Fuel gauge is most likely a bad tank sending unit

Speedo - beats me. Most likely a bad speedo

Oil Pressure Gauge - At the oil pressure sender - ground the center wire of the plug (key on engine off). Does the gauge swing to zero? If yes - bad sender. If not bad gauge or bad wiring.

Temperature Gauge - Find this temperature gauge/temp light sending unit. Key on ground each of the wires watching the dash TEMP light and the Temperature gauge. One should cause the Temp Gauge to peg hot. The other should cause the TEMP light to come on.



This is the temperature gauge sending unit. It has two functions. The wire that connects to the pin that is AWAY from the side notch is for the gauge. The wire that is close to the side notch is for the TEMP light (yes your Fiero has one).

Turn the key on but leave the engine off. Ground one of the wires. Then try the other. One should light the temp light. The other should make the temp gauge (or just pivot in your case) move. Then just make sure the wires are on the correct pins so the two devices work correctly.
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OziDarklighter
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Report this Post04-29-2014 07:53 AM Click Here to See the Profile for OziDarklighterClick Here to Email OziDarklighterSend a Private Message to OziDarklighterEdit/Delete MessageReply w/QuoteDirect Link to This Post
Wow, thank you that's very helpful!
Where would you start out of these? I'm thinking the temp gauge is the most important (and relatively simple?)

Is there a guide to taking apart the instrument panel to test for 'stupid' things, like loose or tight needles?
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phonedawgz
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Report this Post04-29-2014 11:03 AM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
Take off the panel under the dash and find the two screws that go up into the back cover of the dash and take them out. Take out the 5 (I think) screws that hold the back on from the top. They are torx screws. Then the back is off and you can reach most of the bulbs. If needed you can continue to remove the entire instrument cluster.
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Gall757
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Report this Post04-29-2014 12:19 PM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
There is/was a technical problem with the temp sensor in Phonedawgz' picture. It seems the factory wiring was not right. Some cars have been modified to work 'properly' and some have not.

http://www.fierosails.com/tempgage.html
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84fiero123
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Report this Post04-30-2014 08:53 AM Click Here to See the Profile for 84fiero123Click Here to Email 84fiero123Send a Private Message to 84fiero123Edit/Delete MessageReply w/QuoteDirect Link to This Post
it is possible the printed circuit board on the back of the dash cluster has cracked and some of the lines/wires are broken and not making contact. I had an 80s TA that happened to I bought my oldest daughter, not a part you can buy I think anyway but a distinct possibility. to be sure use a test light on the back printed circuit board, or better yet a continuity tester, no power need. just check the lines in the board, is that a deceptive enough name for a flexible peace of plastic on these. sometimes the lines wear out over the decades or have been damaged by a PO removing and reinstalling the cluster or the repeated heat cooling from outside temps.

Steve

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Technology is great when it works,
and one big pain in the ass when it doesn't



Detroit iron rules all the rest are just toys.

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