Various Gauge Cluster Issues (Page 1/1)
AccursedAvocado NOV 28, 02:24 AM
So I'm relatively new to the fiero community, and the car community in general, along with this being my first post, so I'm sorry if my explaination is incomprehensible.

Edit: I have a 1985 fiero with the 2.4L duke and the original manual transmission, I'll post pictures and videos when I can

I'm no mechanic by any means, but I've been trying to learn. I been going through the process of fixing up my fiero and addressing issues as they come along to some success, but thse issues have completely stumped me.

First off, I'm dealing with an issue with my speedometer not displaying while driving. When I got the car it wasn't working, but I just used the tachometer (works just fine) to gauge my speed. The speedometer itself always displays 35mph. At first I figured it was the speedometer itself, and I replaced it to no avail, in fact it also displayed 35mph. I would go in and manually move the dial with my finger only to have it go back to 35. I'm not sure if I failed to plug it in correctly or what went wrong. Is there a speedometer cable that tells it the speed, or is it tied to the tachometer? I'm uncertain on how to troubleshoot.

Another issue I face is the gas gauge phasing in and out of existance. What I mean to say is, The gauge displays correct information, however the needle randomly jumps all the way to the right of the gauge. It stays that way for several minutes, and as the gas levels drop it jumps back to the current position. I've never ran out of gas while driving, but I'd prefer to have certainty. Any ideas on whats going on?

All my other gauges work no problem.

Thank you for any and all help/advice you may be able to give!

[This message has been edited by AccursedAvocado (edited 11-28-2022).]

Eliredandblack NOV 28, 04:20 AM
If you are going to keep the FIERO, a Year Specific Pontiac Service Manual is a must. My uneducated guess is a wiring issue, or the tranny speed sensor for the speedometer. Once you have the Manual, you can start trouble shooting with the help of the included wiring schematic. Remember to be very specific when posting your cars problems, and for us older guys, pictures are also extremely helpful. Good Luck.
dmac35242 NOV 28, 05:21 PM
Post the year of your car as well as the engine/transmission specs.
The fuel level issue won't be related to engine/trans combo but the speedo may very well be.

Google for info on fuel level sending unit. It sounds like the sender is crapping out.
sanderson231 NOV 30, 03:20 PM
Do the trip odometer and total odometer work? If these also don't work, it points to a problem with the Vehicle Speed Sensor (VSS) or the wires between the VSS and the dash. These wires go through a connector under the center console (C-203). That connector can be separated to check the resistance of the wires from the VSS to C-203 and C-203 to the dash. That will help narrow down the location of a possible open or short to ground.

If the wires check out ok then it probably is the VSS which plugs into the transmission. The VSS is just a generator that produces a sine wave with the frequency proportional to the vehicle speed.

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

T Top 88 NOV 30, 10:37 PM
I'm betting Sanderson is on the right track with this one. Another thing I'd check is the traces on the backside of the cluster. Make sure that there is no breaks in them, and get them as clean as you can with a electronic safe cleaner if needed, I'd also make sure that the terminals on the backside of the speedometer and the temp/fuel gauge combo are free of corrosion. I had an issue in the past with my gauge cluster where the traces began to separate from their backing where the different connectors plug in on the backside of the cluster. It caused it to do all sorts of weird stuff, like random backlight lights not working, warning lights to come on for stuff that didn't make sense such as the "BRAKE" warning light with the handbrake off, and different gauges to not work all the time. I swapped out the main housing with one that had perfect traces, and just dropped my gauges, and lights into that. There's other ways to fix stuff like that besides replacement, but I just had the part laying around.

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-White 1988 Fiero GT T-Top (TTOP 88)

AccursedAvocado DEC 01, 12:01 AM
Hopefully I'm replying correctly, still figuring this forum out.

The odometer and trip odometer don't work either. I'm more than certain that the part has been discontinued. Where would be my best bet of finding one? I'm guessing that Rock Auto might have what I need, but I would rather be certain that someone had tried and found a reliable part.

Another thing is I did recently try replacing the entire speedometer/odometer set to no avail.
Patrick DEC 01, 01:02 AM

quote
Originally posted by AccursedAvocado:

I'm more than certain that the part has been discontinued. Where would be my best bet of finding one?



You're referring to the VSS? Ask for one at The Mall.
olejoedad DEC 01, 10:26 AM
Check the plug in the lower left corner of the gage cluster.
sanderson231 DEC 01, 12:04 PM

quote
Originally posted by T Top 88:

I'm betting Sanderson is on the right track with this one. Another thing I'd check is the traces on the backside of the cluster. Make sure that there is no breaks in them, and get them as clean as you can with a electronic safe cleaner if needed, I'd also make sure that the terminals on the backside of the speedometer and the temp/fuel gauge combo are free of corrosion. I had an issue in the past with my gauge cluster where the traces began to separate from their backing where the different connectors plug in on the backside of the cluster. It caused it to do all sorts of weird stuff, like random backlight lights not working, warning lights to come on for stuff that didn't make sense such as the "BRAKE" warning light with the handbrake off, and different gauges to not work all the time. I swapped out the main housing with one that had perfect traces, and just dropped my gauges, and lights into that. There's other ways to fix stuff like that besides replacement, but I just had the part laying around.




Good point on the checking the traces on the back of the cluster. One specific problem area is the copper foil on the inside of the where the connectors plug in the back of the cluster. This coil can come loose and result in a cross connection when the plug is inserted.

The first tool the original poster should acquire is a multi-meter to be able to check volts, amps, and resistance (ohms). This is essential for diagnosing electric problems. Harbor Freight has serviceable multi-meters but I would probably spend a little more to get better quality. The Klein Tools MM400 sells for $43 on Amazon.

I pulled the VSS from a transmission I had in the garage. Drove it with an electric drill and checked for AC volts. The little booger generated 75 volts

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

[This message has been edited by sanderson231 (edited 12-01-2022).]