How does the fuel mileage guage work?

AaronM · 12-04-2002, 04:43 PM

Hey, I'm just curious if anyone knows how the fuel mileage guage on my 1987 924S works. Is it wired as part of the system that controls the shift light? I'm asking because mine isn't quite working right. It's either all the way to the left (when I'm driving) or pegged off to the right (when coasting). Every now and again it will decide to work for a while, but most of the time it only goes into the numberd range when I'm engine braking.

I'm asking because if I remember right the BMW fuel mileage guages were vacuum operated and being a 914 guy I'm rather paranoid about vacuum hoses going bad.

Thanks a lot.

Aaron

Trevor · 12-04-2002, 04:59 PM

My 944's guage worked most of the time but every once in a while it would go all the way left and stick. I'd blame it on VDO's wonderful accuracy and reliability.

AaronM · 12-04-2002, 07:58 PM

Quote:

Never trust a gauge that tells you that you are getting 60 mpg when you are stopped at a traffic light.........

Well, at least according to the manual if you're going slower than something like 16 mph then the guage is supposed to read in gallons per hour (the grey scale just above the white mpg scale). The 0.5 gph corresponds closely with the 40 mpg tick mark. So at a traffic light the guage is probably telling you that you're consuming 0.25 gallons of fuel per hour.

So I guess it's tied into the shift light system somehow then. That would explain why it's not working right. Unless I'm letting kids on Schwinns out-accelerate me the shift light absolutely does not come on below 4,000 RPM. It's never come on below 3,000 RPM no matter how much I babied it.

Thanks much for the information.

Aaron

scottmandue · 12-05-2002, 01:27 PM

I will give a million pesos to the person who will come up a way to convert that useless gauge to a volts gauge!

Nabeel · 12-05-2002, 02:53 PM

Dunno about it being a useless guage. One time after filling up I payed attention to the mpg guage and the shift light, trying to acheive the best possible mpg on that tank. Result? 24 mpg of almost entirely city driving. But it was no fun and I won't be trying that again.

I guess if you really want to be a most virtuous and efficient miser of fuel, you could observe the guage with religious conviction and get some Sierra Club pleasing milage numbers. But then you'll be missing out on the point of driving a Porsche.

scottmandue · 12-05-2002, 03:09 PM

Quote:

Originally posted by Nabeel

I guess if you really want to be a most virtuous and efficient miser of fuel, you could observe the guage with religious conviction and get some Sierra Club pleasing milage numbers. But then you'll be missing out on the point of driving a Porsche.

Quick vote... how many here bought their 944 to get great gas milage?

J/K ha ha

I know I am getting at least 20 mpg on the old 44 and I drive the pi$$ out of it. Funny thing, the harder I drive it the better it seems to run!

Now where did I put my Sierra Club card?

AaronM · 12-05-2002, 04:27 PM

Quote:

Originally posted by scottmandue

Quick vote... how many here bought their 944 to get great gas milage?

J/K ha ha

I know I am getting at least 20 mpg on the old 44 and I drive the pi$$ out of it. Funny thing, the harder I drive it the better it seems to run!

Now where did I put my Sierra Club card?

Hey, I bought my 924S because I figured that I could get close to the same mileage as the Accord I'm getting rid of. (Accord gets 29-30 mpg on the freeway, average tank of mostly 55mph driving is 27 mpg.)

Aaron