athenian

If anyone knows how the fuel consumption gauge works (wiring/sender/items to look for) in a Euro 928S, please post it here....

Mine is an 84 S, Auto and the fuel gauge USED to work last year!! (see photo)... I have no idea why is not working now; The car was parked all winter and I rarely use it....I haven't replaced anything in the instrument cluster and all the other gauges seem to work well.....Okay, the speedo sometimes (not always) "sticks" upon startup but comes alive within a mile or two of driving down the road....So I'd say the speedo works okay....

My thinking is to take the cluster out and check the circuit board in the back of it since I need to replace the lighting bulbs anyway....Does anyone know what to look for on the printed board??? I'll take a couple of photos while I'm back there if anyone needs them.

In the meantime, if anyone knows how the fuel consumption gauge is wired or how it supposed to work (vacum, electical or things to check) please post it here.....

Regards - VK
84 Euro Auto

Paul D

VK - My consumption gauge broke last year. It appears to be all electronics that drive the needle. I do not know where/what the sender is. The rear of the instruments is more like a flex-tape circuit than a circuit board. I removed all this to fix the odometer gear and replace the instrument lights with high intensity LED's. It amazes me that there arn't more electrical issues with these instrument clusters. The connectors used for the connections to the flex-tape don't appear too rugged. There doesn't seem to be any locking mechanism from the wiring harness connectors to the flex-tape. They simply slide on. I'm not arguing though, I'm just glad they are working well on my car. I design alot of test equipment cables that mate with military flight computers. The military has some very nice hardware when it comes to connectors. After I cleaned and reassembled the cluster the gauge still does not work... Oh well, time to dig out some wiring diagrams.

athenian

Thanks for the photo and info Paul...

I'm tempted to take my cluster out to change the bulbs as well....I was thinking of installing larger/brighter bulbs for the lighting, but not high-intensity LEDs....Anyway, getting back to the consumption gauge problem - if you find anything interesting in the wiring diagrams PM me, if you'd like...I will attempt to clean the electical connectors as well to see if that makes any difference.

Vasilis
84 Euro S auto

Vilhuer

Consumption is counted from time injectors are open. As approximate fuel pressure is known since it's hoped to be constant by design and size of injectors is also known it was easy for Bosch engineer to calculate consumption from injector duty cycle and road speed. This is reason why gauge appeared at same time as L-jetronic injection. There isn't all needed data readily available in mechanic K-jetronic. Sounds like gauge problem when engine is running properly and speedo is working.

D_Schultz

That sounds like a fair explanation, but I have an '83 euro K-jet that certainly has a functioning consumption gauge (and I usually have it swung pretty far to the right ).

Vilhuer

True, forgot '82 and '83 Euros. There is processor in them that gets info from airflow sensor, tacho and speedo and calculates instant consumption based on those. In L- and LH-jetronics information is readily available without need for separate measurement.

Mark

The old ('83) 944's have these, too...

marton

I have a euro 81 928s (82 model) which has a fuel consumption gauge - according to the www.porsche.com site - "New features for the 82 standard 928 and 928 S included a petrol consumption display".
This processor that somebody mentioned, that gets info from airflow sensor, tacho and speedo - does anybody know - is this processor simply to feed the petrol consumption display or does it have any other function?
I was surprised I did not think I had any electronics - nor do I have a MAF - so from where does it get airflow info?

Vilhuer

Air Flow Sensor (housing for large air meter flappy underneath Fuel Distributor) has different part number for '82 model year. PET gives Consumption Indicator as reason for change.

All other related systems seem same except Instrument Cluster Back Plate. Same reasoning is listed for it's change also. My guess is that all logic is in there. It has speed signal already anyway and it likely gets either direct vacuum or electric signal from Air Flow Sensor. US model documents only talk about how it's done in L-Jetronic enviroment so no help on Jim M's CD's AFAIK.

I don't believe more mechanic Euro or electronic US/later Euro systems to be very smart even though prosessor is mentioned in Jörg Austen's book.

athenian

Soooo, if I understand this discussion correctly, all the engine signals are present but my gauge is dead...

Is there a way to test those "signals" to make I'm getting the correct inputs to the cluster??? Those of you with access to EURO wiring diagrams, which wires are supplying these signals in the cluster and where are they located??

Thanks - Vasilis

84 Euro Auto

heinrich

I want one for my S4

TM___

This thread is almost 20y old, but just about the only one I can find on the fuel consumption gauge.

My car ('84 EURO 928S, manual) hasn't got one, but I may want to retrofit it, just because.
(I know, the car is very thirsty, and I don't really care about its consumption, but the extra needle just looks cool to me, especially on a 40y old car.)

Question is, does the car have all necessary wiring already in place, and is this just a matter of getting and installing the right tachometer? Or would it need a lot more to do so?

BRB-83-911SC

84 Euro should have fuel consumption guage from factory. My 5-speed does.

TM___

If I read the PET correct, it is only standard for German market cars from 85+, not in other European countries. Not sure if it was an option on other cars, or if PET is simply incorrect.
It's not present on my (Spanish) '84 Euro 5sp and the original booklet also mentions nothing about it. The rev counter is depicted without consumption indicator, though there is one overview photo in the booklet which has a cluster with such an indicator.

Do you know what it is connected to in the car? Once I open up mine, I'll check if I have the necessary wiring in place.

Tops2808

Here`s my 86 German market , with fuel consumption meter. Cluster foil will be changed during the winter