924Board.org

joecitizennn · Joined: 12 Sep 2005 Posts: 2096 Location: no mans land

My 87 924S has always averaged between 27 to 28 MPG. Recently it has dropped to 19mpg. All services are up to date and the fuel system is spotless. I am wondering if I have a computer or sensor problem. Has anyone had a similar problem?

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

O2 or temp sensors?
_________________
Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

joecitizennn · Joined: 12 Sep 2005 Posts: 2096 Location: no mans land

is there a good write-up on testing these items?

D Hook · Joined: 02 Nov 2002 Posts: 3158 Location: Omaha, NE

Winter-blend fuel maybe?
_________________
'80 924 n/a SOLD

brupska · Joined: 27 Aug 2009 Posts: 150 Location: Indiana

I was gonna ask where do you live?? Cold climate?? MPG will drop off from more air comming in which the car will have to mix more fuel to match!!! I don't know much about the Fuel system on the S model though.

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

The best test for an O2 sensor follows:

1. Two years old (Y/N)?

A yes to the above indicates replacement.

To avoid the Porsche parts premium, order Bosch "Universal" sensor, #15725. Got mine on E-Bay for $20.
_________________
Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

joecitizennn · Joined: 12 Sep 2005 Posts: 2096 Location: no mans land

I was told that it was winter grade fuel by other people too, but that cant be the case because my 1988 924se which has been getting a steady 20mpg is now getting 25mpg after I did a full service including vacuum lines and breather tubes. And that is with winter grade gas.

Thanks for the tip on the 02 sensor.

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Did you use a kit for your hose service?
_________________
Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Paul · Posted: Fri Feb 12, 2010 10:57 am Post subject:

Odometer slipping?

Different tires?

Is the inside of your tail pipe all covered with black carbon?
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

Mav666 · Joined: 16 May 2008 Posts: 47 Location: Newcastle, UK

brupska · Joined: 27 Aug 2009 Posts: 150 Location: Indiana

Lots of carbon on a tailpipe just means that your car is running rich. Something is making your car burn more fuel then it is supposed to.

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

Fuel with 10% ethanol tends to cause the oxygen sensor to read slightly leaner and therefore the efi system will increase the amount of fuel to compensate.

Might be worth checking next time you get fuel.
_________________
Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

Mav666 · Joined: 16 May 2008 Posts: 47 Location: Newcastle, UK

I do run it on Shell 99 every now and again, and when I do it does seem to run richer