darkvoltage

Hi all. I have a gas guzzling problem. Not to say that I bought the 964 for its fuel efficiency, but I am getting about 9 mpg, or about 27 L/100km. This figure is both what I calculate at the pump and off the OBC. The specs I read for the 1991 C2 Tiptronic is about 15-20mpg. Could be because it's winter (just abouve freezing); was a touch better in the summer (about 15mpg). It is better on the highway. again about 15mpg. The car has 48000mi, and is otherwise in good condition. Is this level of fuel consumption 'normal' for a car that is a daily driver, about 100km/wk and consumes about 1L oil/1000km? Thanks.

Steve Weiner-Rennsport Systems

Hi:

How old is your oxy sensor?

Thats the single biggest reason for lousy mileage.

When these get old, they are sluggish to respond and may not operate through their full range.

jimq

The worst I get is 13-15 in town but usually about 25-27 if on the highway at 75 or so. Doesnt get all that cold here but yours doesnt sound right at all! I also have a 91 tip.

eddychan

I also have a 91 tip, I have similar mpg with Jim. Yours is far too high. It will cost you a lot if you were in Hong Kong when Fuel is about 1.48 us dollar per litre which means 6.73 US dollar per gallon ( 1 gallon = 4.65 litres, 1 US dollar =7.6 hk dollar)


Happy motoring!

Eddie

garrett376

How heavy is your right foot?? Maybe you driver like a drag-racer?? Driving style is the biggest affector of fuel economy as long as no check engine lights are on or black smoke coming out the tail pipe indicating a faulty engine.

darkvoltage

I don't think I drive too fast as I haven't got a ticket in over 10 years, but then I could just be lucky. Also driving primarily (90%) in the city tends to limit speed. I do tend to stomp in it off the line, very satisfying since I don't drive too far. I drive every cold morning without warming up about 2 miles to work, engine just about warms up by the time I get in. Same story in the evening. I thought it may be caused by running a cold engine, and I guess it's plausible that it's my driving style.

There is no black smoke, although there is some white exhaust when really cold. Never replaced the O2 sensor as far as I know; no lights come on. Except that very rarely, the 'CAT' light turns on, flickers, and goes away after I yell gerrrWOOOOF' as I blast off.

PC2

I drive 60% City and 40% Highway. Use the manual mode most of time and my OBC indicates MPG average of 17. You may want to give it some Techron because I've noticed improved milage & engine respond after each treatment.

Adrian

I suspect you are stuck in open loop mode and running rich all the time. However before going any further we will need to know the configuration of your 964. Being from the UK it could be with emissions, without emissions or somewhere in between. Recently on another forum we found a 964 owner reporting similar type issues who discovered his workshop had replaced (as requested) the cat with a bypass but had also removed the O2 sensor. All problems were solved when the sensor was reinstalled.
Ciao,
Adrian
964C4

Christer

I don't have an O2 sensor anymore, and I get 28+ on the motorway at around 80mph (not that I ever drive that slow of course) and average around 20-23mpg on a 'mixed cycle'. Importantly (perhaps) my DME is jumpered to ignore O2 sesnor input.

Adrian

Dear Christer,
The jumper is not to ignore the O2 sensor it is to use a different set of calculations, inputs such as an alttitude sensor and to use a different set of maps to allow use of the closed loop system. There is a huge difference in not just having a O2 sensor and having a system adapted to work without it.
Summary: You do not have an O2 sensor but you have something which replaces it.
Ciao,
Adrian
964C4

Christer

Hi Adrian

Yes, that would be a better explanation - but basically what I meant. Although in my defence it was described to me 'as ignoring any O2 input' - I blame the technician!

Irishdriver

I normally get 13 to 16 litres/100km tooling around on the bordcomputer. This matches with the petrol pump/milage calculations I do once in a while.

I once set the the bord computer to zero at the start of a slalom and got it to read 32L/100km for a while but 5 mins on the road brought it back down to 16 or 17.

27L/100km means the car is unwell or the driver has a Nigel Mansell on/off driving style.

Arjan B.

Your consume is too much, but that is no news for you i think.
I suspect to a O2 sensor, but don't forget there are more things to look after.

Air filter polution
Spark plugs
Combustion [valve adjustment]

And don't forget a wrong Chip in your DME could be a great cause of high fuel consumption.

Do the DME reset, and try a few weeks. Then reckon what your consume is.
1 liter on 1000 km oil consume is a bit high, I don't know how you use your car, but in normal traffic 1 liter on 4000 km is pretty average.

tierraman

Just for comparison.....I have a 92 tip, 87k miles and average 18-19 mpg at 5000 ft altitude, combination driving.

pete000

Fuel filter?
Injectors dirty?
Air filter dirty?

Try some Chevron Techron, but I doubt it will make that big of an improvement. I run a bottle through about every 10 tanks of fuel.