Poor Fuel Mileage ? - Where to start?

Wagon Boy · #1 (**permalink**) 07-18-2005, 10:47 AM

Hi BMW Friends

I am a half-decent shade-tree mechanic. My '92 525i wagon gets 14.5 mpg and I figure it should do 20. Where is the best place to start? Plugs and O2 sensot? Those are my first thoughts. I have about 75,000 miles on the clock and it appears the 60,000 mile service was done. I also have a loud exhaust and I think the muffler is shot. ANy advice> Also, I don't knoe how good the OBD is on this model. Could it tell fi an O2 sensor is bad? Should I have a pro look at it first or just have at it with some fresh parts? Thanks all...

540izzle · #2 (**permalink**) 07-18-2005, 07:39 PM

Quote:

Originally Posted by Wagon Boy

Hi BMW Friends

I am a half-decent shade-tree mechanic. My '92 525i wagon gets 14.5 mpg and I figure it should do 20. Where is the best place to start? Plugs and O2 sensot? Those are my first thoughts. I have about 75,000 miles on the clock and it appears the 60,000 mile service was done. I also have a loud exhaust and I think the muffler is shot. ANy advice> Also, I don't knoe how good the OBD is on this model. Could it tell fi an O2 sensor is bad? Should I have a pro look at it first or just have at it with some fresh parts? Thanks all...

I think your muffler shot and the 02 sensors that are bad are causing the bad gas mileage.

Calypso34 · #3 (**permalink**) 07-18-2005, 07:59 PM

Wouldn't be bad to check your tire pressure either.

BMWimportRcR · #4 (**permalink**) 07-18-2005, 08:16 PM

check your coolant temp sensor it might be running cold all the time meaning its gonna run rich or check your air filter

Wagon Boy · #5 (**permalink**) 07-19-2005, 07:25 AM

Thanks for the responses!

I could change the O2 sensor. Is there a way to test the O2 sensor? Can the OBD tell me anything? I had it emmissions tested and I got readings of: HC .067 Grams, CO 3.489, CO2 484.8. Does this mean anything to anyone? The HC rating is almost to the limit.

Would the bad muffler effect the mileage? From lower back pressure?

The coolant temp guage is right in the middle and seems to respond okay. Tire pressure is good and the tires are new. THey are Conti Extreme Contact 225/60/15s and I don't think they get great mileage. Could it just be the tires?

All responses are welcome.