Venom_1138

Just picked up my dream Trans Am yesterday, a 1985 manual transmission diamond in the rough. She may not look like much, but she's got it where it counts.
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Anyway, one of my first fixes is the gauge for the fuel, engine temp and CEL and parking brake lights. (the leftmost gauge cluster). Engine temp does not work, fuel gauge only moves between 1/4 - 1/2 tank, but isn't reliable enough to depend on to tell how much gas it actually has. The parking brake light is always on, and the CEL pops on after a few minutes of driving. The previous owner said he had the CEL light issue for years and couldn't find the cause.

My thinking is that with virtually every part of that gauge group malfunctioning, there's probably either something wrong with that particular section itself, or I have an issue elsewhere that's just throwing that entire section out of whack. I was wondering if anyone had any suggestions as to how to narrow down the cause of the problems. I've never done anything with gauges and the like, so I'm kinda venturing into new territory here. 😉 If anyone could just give me a good jumping off point that would be awesome. Thanks!

John in RI

iTrader: (167)

Your car is going to have a cable operated Speedo Cluster. The only clusters that have a cable Speedo are 82-85 Firebirds. ( + Some non-gauge 86 cars too ! )

The first thing I would suspect here is the cluster itself. Possibly the printed circuit on the back of the cluster to be more specific. It's VERY POSSIBLE that you've got a bunch of minor issues that collectively appear to be a cluster problem too - so I'd check each issue individually when possible to see if you can isolate the bugs.

Check the temp sensor wire is connected on the driver side head,......

Check the brake wire at the E-Brake Handle and the Brake Wire at the Master Cylinder,......

Check for Engine codes,......

And so on.

If you can't correct the problems 1-by-1,.... then I'd turn my focus to the cluster.

Venom_1138

Thanks for the reply, the cluster being faulty was my first guess as well.

However, it looks like it may be more of a case of multiple issues that just happen to report to the same cluster. My brakes were really soft, and needed to be bled because there was a significant amount of air in the front brake lines. Once I completed that, the brake light quit being constantly on and now only shows when I engage the parking brake.

Upon further inspection, I also found the vacuum line for the purge valve had petrified and broken. I replaced it, hoping to possibly find the source of the check engine light, however while I was unable to clear the engine light, I did find that the temperature sensor was completely broken. I've got a new one on order from AutoZone, so when I get it installed hopefully I'll get my temperature gauge functioning again.

At this point, I'm inclined to think there's just a myriad of issues and by chance most happened to share the same cluster. The previous owner certainly did a few half-brained "fixes" here and there, but she's a tough one and she's survived the neglect. I'll update once I'm able to get the new temp sensor and verify if that solves the temp gauge issue.
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Venom_1138

The real head scratcher here is the fuel gauge. I've been reading up other people's posts, but it sounds like most everyone has had the gauge either stay at full or empty but never move.

My issue is that the gas gauge does move, but not much and only between around the quarter tank mark to a bit below the half tank mark. If I fill it up, it will move toward the half tank mark and work its way back towards the quarter tank mark as it uses fuel. But that's actually even less helpful than it sounds in terms of knowing how much fuel I have remaining, so I'd really like to find a solution.

Because the needle does move, is there some way to test just the fuel gauge by 'tricking' it into thinking the tank is full or empty so it will try to move the needle accordingly? My other theory is that maybe the needle is somehow just stuck in that area, but I'm guessing the only way to test that is to pull the dash and try to access the gauge that way.

Does anyone have any other suggestions as to how I could pinpoint the source of the problem? The needle is trying to do its job, I'm just not sure what the easiest way to find what's holding it up would be in this scenario.

EDGE

Take the cluster out and clean all the contacts including all the screws that hold the gauges in. I've just been through this. They are probably green and corroded

Venom_1138

Thanks for the suggestion, that actually makes a lot of sense as to possibly why the gauge is responding to the change in the fuel level but isn't displaying correctly. Since it's basing the level of fuel off the amount of current it receives, corrosion could be preventing an accurate reading. If nothing else, this will at least give me a good jumping off point.

Barring that, from what I've read, the next possible culprit could be the fuel sending unit. Really hoping that isn't the case, mostly because I'm not terribly excited about the prospect of dropping the fuel tank. I'll give cleaning my contact points a go first and update the thread from there.

Venom_1138

Replaced the temp sensor and the broken pigtail yesterday, but the temperature gauge still doesn't give any reading. I never really paid attention to it's behavior since it wasn't working, but as I was watching it after replacing the sensor, I noticed that it does jump all the way to the right (max temp reading) when I turn the key to start the engine, then drops back to 100 (lowest possible reading) as soon as the car starts. So I guess at least I can say that the gauge isn't seized or otherwise unable to move... 🙄

Next step is to remove the cluster and check/clean all the contact points. I'm going to wait a few days before I do, though. I ordered some LEDs to replace the existing dash lights since they barely illuminate the panel as it is, so I'm just going to do everything in one shot in the interest of saving time.

While I have the gauge panel removed, is there any other maintenance or repair anyone can suggest I make beyond cleaning my contact points and replacing the existing dash lights?

Venom_1138

I pulled the fuel/temp gauge cluster and cleaned the contact points. Some of the instrument lights didn't work due to mild corrosion, so I took some fine grit sandpaper and cleaned the contacts. That resolved the problem with the lights, but unfortunately the temp gauge doesn't give any kind of reading and the fuel gauge still doesn't move the full range.

Is there any way to test the gauges themselves to verify whether they're working properly? I know that odds are the problem is elsewhere, but I want to rule out the simplest part first.

Is there a way to replace just those indivual parts of the gauge if either turns out to be faulty?

NINÅ

Venom_1138

Thanks for the reply, I had a couple of questions about the method described, though.

Regarding the fuel gauge, there aren't any wires going to it, per se. It has 3 studs coming out the back that clip into the back of the gauge cluster, which all receive signal from the printed circuit board on the back. Do I just pull it from the housing and connect a couple of jumper wires between the gauge and the circuit board terminals?

Regarding the temperature gauge, I do receive some power/signal going to it when I go to start the car, as the gauge will swing all the way to the right/max temperature reading when I engage the starter, although as soon as the engine starts it drops back to 0. So in that regard, I don't know if it's already doing what you described... maybe I got a faulty replacement sensor?

NINÅ