fuel consumption out of control

[bavarian]

i got an 1989 535i with an e32 engine, (735i). I'm using about 27 l/100km.
Tank is full, average usage tells me 17.2 l/100km
range as per obc 210 km.
how can i get the fuel usage down. it happen out of the blue. used before about 12l/100.

what can i do.

[ThoreauHD]

O2 sensors, spark plug and ignition coils, err.. what else helped. Higher octane fuel. Synthetic oil. Fixing vacuum leaks.. That's about it.

[bavarian]

02 sensor is new, plugs as well as coil. use unleded 95

[BillionPa]

leaking out of the charcoal canister?

[Kalevera]

How's driveability? Any noticeable change in power since the fuel consumption went way up?

Anything's par for the course. Carefully go over the car. I had an E32 735 last week with nearly locked front brakes -- customer was complaining about hesitation and lack of power (Hmmm!)....I suggested maybe his fuel consumption was also going down, but he was still getting 18mpg. What about the AFM and wires? How's the vacuum -- any signs of carbon buildup on the valves?

An '89 euro car likely doesn't have a charcoal canister -- vapors would have been vented to the atmosphere.

best, whit

[bavarian]

no change in power

[BillionPa]

all E34 models, euro and usa, should have the canister.

early models used a different canister, but since 6/88, all models should use the same one.

if the original canister and valve are on there, i could imagine a failed valve causing heinous fuel leaks in combination with a vacuum leak.

however, other things may be causing it....

a failed injector
a leaky gas tank
a broken or rusted out fuel line
a siezed brake caliper(s)
bad ps pump, water pump, or alternator (usually hard to start in this case)
AC compressor clutch could be toast (and this one)
any sort of sieze along the drive line, like rear diff, center bearing, transmission.

if that last one is the case, you can test by putting the car on jack stands in neutral and trying to spin the rear wheels. spin each one individually to test the rear diff and wheel bearings, then spin both together in the same direction to test everything else.

[Toomas]

Start the car, warm her up so the temp cauge is in middle, and go behind her and smell the exhaust.
If you can smell unburnt gas then shes running rich.

If thats the case then if possible try another air flow meter and ecu.

Also you can try to disconnect the cold start injector.

[Ausmpower]

Again I'll say it............. DME temp sensor!

[BillionPa]

air intake temp sensor would indeed cause bad mileage if it was way off, since it tries to guess the density of your fuel.

[genphreak]

How's driveability? Any noticeable change in power since the fuel consumption went way up?

Anything's par for the course. Carefully go over the car. I had an E32 735 last week with nearly locked front brakes -- customer was complaining about hesitation and lack of power (Hmmm!)....I suggested maybe his fuel consumption was also going down, but he was still getting 18mpg. What about the AFM and wires? How's the vacuum -- any signs of carbon buildup on the valves?

An '89 euro car likely doesn't have a charcoal canister -- vapors would have been vented to the atmosphere.

best, whitYep, so many things to check. But usually the result of inproper maintenance... otherwise most of the things people are suggesting can be taken off the list.

Whit, in yoru experience do you notice the AFM sensors dieing or is it the coolant sensors that tend to go? I've had to do these before, I consider them a must do on an M30 beyond 15 really, though i guess one can wait till they die, but why bother... bolt out bolt in and bleed. Never worry it's dead again (or slightly off)... :D with gas prices the way they are one wants it running just right!