fuel consumption guage/display

[ltadpole]

Hello,

Did anyone of you know the operational theory of the fuel consumption guage(display). It is the guage which estimate how many miles you can run in 1 liter gas!

Recently the guage in my S320 stop function properly!

Thx!

[cole3986]

The gauge measures engine vacuum. The higher the vacuum the better the gas mileage. Very Very old technology- my 68 Barracuda had a the same gauge.

[Brett San Diego]

the ECU. I suppose that would only apply to newer electronic ignition cars.

Brett

[ltadpole]

Thanks for the reply. Can you tell me more which part should I change or did anything wrong with my engine vaccum or fuel injection system?

[Brett San Diego]

an electrical signal (bad sender or bad electrical connection in the circuit) or the gauge itself is bad.

The best thing to try first is connecting a different instrument cluster that you know works to narrow down the fault between the gauge/cluster or something else on the car. Got a friend nearby with a W140?

Brett

[ltadpole]

Thanks for Bett's suggestion. I think the malfunction is mainly due to the electrical signal (bad sender or bad electrical connection in the circuit). The guage is still moving but just cannot show the correct reading or response in the correct way.

Do you know where to locate the sender or electrical connection?

[myarmar]

The signal for fuel consumption guage coming from LH control module. You can check instrument cluster including fuel consumption guage. Follow procedure here:
http://www.mercedesshop.com/shopforum/showthread.php3?t=51415

[ltadpole]

Thanks for the details description posted by myramar.

I came across this kind of information before but seldom know there is a small button inside the clock turning knock!!

I have tried the test and all the displays behave correctly.

I just wonder whether there is something wrong with the vaccum pressure!

[myarmar]

Fuel consumption guage doesn't read vacuum. It gets electrical signal from fuel injection computer.
Did you get reasonable reading in step 2?
When vehicle stopped step 2 shows consumption in L/hour;
When vehicle is moving display automaticaly changes to L/100km.

[ltadpole]

Dear Myarmar,

Thanks for your suggestion again. The reading in step 2 is quite reasonable. I drove the car this morning for a short trip (12.8km). The reading is 2_0. I guest the car consumed 2L gas for this trip.

Every reading in the test is normal and all displays / guages functioned well in the test. I suspected the electrical part! Just don't know how to test the fuel injection!