Any way to know how much fuel in tank?

[StereoInstaller1]

Yeah, late gauge reads bad in early cluster too.

[ak-]

Suckers. $2.73 for 91 here. :D

lol, that's still more then our 87 octane.

[Jand3rson]

I can tell you that when I put a 89 cluster in my 86 it happened to me.

Did it really normally until it got to that point?

[E30SPDFRK]

Not sure. I got pissed off with it quickly and changed it. Now it works like normal.

[Jean]

Really? I have never heard of that! Can anyone else verify this? So when I fill it up, it should be normal all the way until it gets to dead empty, and will then go back to 1/2 and the light comes on? And a seta is an '88, so that would be considered a late-model (facelift tails and wheel arches).

When I first put it in, it was reading just a little over 1/2 a tank. So I've driven it a few times since then, and now it's dead on 1/2, and the light is on.

That is correct! Whenever I install a late model cluster in my early car, the fuel gauge reads wrong...you have to rememember that the low fuel level light is a on/off switch, so it doesn't matter if the gauge reads right or wrong...the on/off is right.

I have a late model cluster in my car, and the fuel gauge itself is from my original / early cluster and everything works as it should.

So, I would swap the knowing good fuel gauge from your previous cluster and it should be fine.

[Jand3rson]

Well, I'll get on that! I still need to find a super-eta tach. Anyone got one?

And all this just because I wanted my tach to read 6k instead of 5k. I just wanted to see my real redline. IS THAT TOO MUCH TO ASK???

[e30Matt]

The late model gauge in an early chassis will read double what's in the tank, because it's designed to use both senders (which are variable resistors) in series instead of a single, thus dropping the voltage returned to a much lower value. When it sees a much higher signal from the sender (due to there being only one), it reacts accordingly and reads higher because it's calibrated for a lower signal.

The early model gauge works exactly the opposite, reading full at a full tank, but empty at only half a tank in a late model, due to the lower voltage return signal.

The gauges are not interchangeable between chassis, but they are interchangeable between brands (VDO/MotoMeter).

[Jand3rson]

So I can't swap the eta fuel gauge into the super eta cluster? Maybe I'd better just go back to the eta cluster. At least everything in it works!

What about if I went to an early ('87) 325i cluster? I know that the revs would be higher than my car goes, but the tach would still read correctly.

[Jean]

Basically the fuel gauge needs to match the sender (or the tank or ultimetely the car/chassis/gas tank it originally came in).

Late model cars had two senders as e30matt said above, you can download the ETM for the two cars and see the difference there. That's why the gauge reads incorrectly, unless you swap it between the clusters.

[Jand3rson]

Is the SI board in my seta cluster swappable into an eta or a 325i cluster? We JUST changed the batteries out, and I'd hate to have done all that work for nothing. Ideally, I'd really like to find another seta cluster.

[e30Matt]

So I can't swap the eta fuel gauge into the super eta cluster? Maybe I'd better just go back to the eta cluster. At least everything in it works!

What about if I went to an early ('87) 325i cluster? I know that the revs would be higher than my car goes, but the tach would still read correctly.

Yes, you can swap the eta fuel gauge into the super eta cluster. I drive a super eta myself and am currently running an '87 iS cluster with an '89 fuel gauge in it to match the sender setup my car has. Reads perfectly.

[Jand3rson]

Awesome. Well, I'll do that when my new tach gets here, just found one to replace mine, I think the unit itself has issues. We've taken the whole cluster apart, cleaned it, put in the right coding plug, changed the SI board batteries, and it still won't read right. It just jumps up to 2k as soon as you start the car, and only moves when you run the revs way up, at which point it just falls dead to zero, and then jumps back to 2k.

[e30Matt]

Sounds like the motor in the tach has eaten shit. New one should fix that.

[Jand3rson]

Dammit Matt, you are just one great big help! You get a gold star.

And I LOVE the quote in your sig. One of my favorite movies.

[e30Matt]

It definitely helps that I went through this EXACT issue with my '88 not 6 months ago, so it's all still fresh in memory. That, and hours of dissecting the ETM wiring diagrams one by one. :)