Economy gauge erratic

[John 535is (Sydney)]

Driving along today and the economy gauge needle is just doing whatever it wants. Under acceleration it would start to read where it should, then just start moving from full left to so far right it disappears. Any ideas or past experience ?

John '89 535is, Sydney

[Paul in NZ]

check that the obc speed/distance is reading ok

[John in CT]

a simple vacuum guage. Back in the day there was a "race" across America called the Mobil Fuel Economy Run which challenged the drivers to milk the most MPG out of the bottom rung of American cars, like the Rambler American, Ford Falcon and the like. The pocket protector-types whp participated all used Vacuum guages and studied them like hawks all the while.

After some years the general public (those few who actually took some notice...) lost interest completly and the series was abandoned. Perhaps it was the 0.25 USD/Gal pricing of the day....

Bet we see a comeback here...

BR,

John
1995 525im

[John in CT]

http://www.thompson-motorsports.com/econ.html

[wingman]

I would suggest that it's all part of the dodgy early E34 dash problem. See www.bmwe34.net for more info.

[rob101]

a simple vacuum guage. Back in the day there was a "race" across America called the Mobil Fuel Economy Run which challenged the drivers to milk the most MPG out of the bottom rung of American cars, like the Rambler American, Ford Falcon and the like. The pocket protector-types whp participated all used Vacuum guages and studied them like hawks all the while.



no the economy gauge is not a vacuum gauge.

[wingman]

no the economy gauge is not a vacuum gauge.

Are you sure? I thought it worked of manifold vacuum.

[mamilapon]

Driving along today and the economy gauge needle is just doing whatever it wants. Under acceleration it would start to read where it should, then just start moving from full left to so far right it disappears. Any ideas or past experience ?

John '89 535is, Sydney
Mate, I used to have the same issue with my E28 until I replaced the rechargeable nicads on the SI board. So if you also have diffeculty resetting your service lights I would say its those batteries.

[myles]

There are no batteries on in the dash of the E34. The SI details are stored in a flash ic.

[Paul in NZ]

i would guess its the capacitors then

[rob101]

Are you sure? I thought it worked of manifold vacuum.
well it certainly doesn't act like one, otherwise i am surprised to find that my car has the same vacuum in the manifold at idle as it does on full throttle:p it has to combine the speed reading with either vacuum (which i don't think it does because there is no MAF sensor in the manifold or vacuum line going to the cluster AFAIK) or a fuel injector duty. so my meaning is if you think its going to act like a normal VK commodore or similar vacuum gauge you will think its broken when it is operating normally.

[mamilapon]

That's one more thing i know now about E34's!!

[genphreak]

Driving along today and the economy gauge needle is just doing whatever it wants. Under acceleration it would start to read where it should, then just start moving from full left to so far right it disappears. Any ideas or past experience ? John '89 535is, Sydney If the engine is behaving normally whilst the gauge is haywire, its in the dash or the feed signal it gets. Sure it could be the capacitors dying out but I would think others here would have noticed it happen before you John. Check your dash connectors are clean (a wipe with ispropyl alcohol) and check also the loom connectors, if someone has installed an alarm or other device they may have 'tapped into 12V' in the wrong place... it really sounds like a bodgey connection or a poor wiring job- but it is easy to pull the gauge panel so perhaps a resolder of all the joints on its PCB would yield a result also... good luck- and let us know how you get on...