Late 944 MPG gauge

[Eskozki]

Hi,

After cleaning grounds and installing an active sub to make listening to music on the 944 a little more enjoyable I found that my MPG gauge stays at the far right all the time. Before it used to zero itself after turning or ignition but not anymore. I tried removing the amp ground to see if that caused interference but no change in MPG gauge behaviour.

Is this gauge purely information or does the computer adjust something based on the signal? Not much info was found online about how the gauge works.

[944 Ecology]

The gauge is purely information from the ECU. It takes the speed from the speedometer sender on the transaxle and calculates the fuel used based on the specified fuel pressure and the injection pulse width and moves the mpg gauge accordingly.

[Eskozki]

Thanks for the info, also found out I burned the interior light fuse and that caused the MPG gauge to stop working, after replacing that fuse the MPG gauge is working again. Interior lights are also a mystery because they're on constantly. I checked the door switches and they look to be good and cleaned them but no change.

[originalowner]

Is the switch on the interior lights set to be on always?

[Eskozki]

On the light the switch is set to always off. No matter which side I flip the switch the light will stay on. I read on another forum that the rear hatch is a possible reason and they're wired with the gas struts. As mine are powder coated replacements I have extra wiring to make the rear defrost work. I'll try to remove the wiring and see what happens. I don't really need the rear defrost anyway.

[Eskozki]

Rear hatch wiring was the issue, and the door switch didn't ground properly on the passenger side. Seems like spring isn't strong enough to close the circuit when the door opens. Needed to pull the switch to get the light going. Some relay went absolutely crazy when messing with the door switches.