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Bad gas mileage at ilde?

1K views 7 replies 7 participants last post by  fryntyr 
#1 ·
On my 93 525, I wasnt positive on which way the cluster needle for the gas mileage is suppose to go. But it seems as though I get horrible mileage at idle. It goes to the 0 side instead of the 40 side. Is this correct? im averaging between 15.9 and 17.4mpg with almost all hiway. The exhaust has an odd smell sometimes like I have never smelled before. Not coolant, rotten eggy or a rich smell. Its smells chemically kinda. Ive been working on cars for 20+ years and have never smelled anything like it.

The valve from the brake booster to the intake has a nipple on the underside that is broken and sucks air into itself. Is it suppose to be plugged or is it suppose to take air into it? Is there a hose that is laying out of site that has broken off of it?
 
#4 ·
If the car is not moving, you are getting 0 mpg. The gauge is working correctly

First thing I would do is repair the vacuum leak at the booster. Then before I condemed the cat convertor I would be looking at an O2 sensor. Before that I would be looking at tune up items like plugs, wires, injectors.

Your milage seems a little low for an M50 525. Could be a lot of things, heavy foot, auto trans, even a small amount of stop and go mixed in, or what you city folk consider highway driving sometimes;)

My 535/5 averages about 24, mostly highway, but I run it hard too, everytime it goes out.

We really need a whole lot more info to be much help.
 
#5 ·
If it smells like a fire-cracker...that's the combination of nitric oxide and nitrogen dioxide (NOx). It's from running near or too lean. Any significant vacuum leaks or deficient fuel delivery would definitely be suspect.
 
#6 ·
On my 93 525, I wasnt positive on which way the cluster needle for the gas mileage is suppose to go. But it seems as though I get horrible mileage at idle. It goes to the 0 side instead of the 40 side. Is this correct? im averaging between 15.9 and 17.4mpg with almost all hiway. The exhaust has an odd smell sometimes like I have never smelled before. Not coolant, rotten eggy or a rich smell. Its smells chemically kinda. Ive been working on cars for 20+ years and have never smelled anything like it.

The valve from the brake booster to the intake has a nipple on the underside that is broken and sucks air into itself. Is it suppose to be plugged or is it suppose to take air into it? Is there a hose that is laying out of site that has broken off of it?
Have you tried pulling the error codes via the stomp test ?
 
#7 ·
Does the broken part pull air all the time? If so fix it.
 
#8 ·
If you do the O2 sensor, spend the $15-$20 and go ahead and swap out the Coolant Temperature sensor as well. The CTS is what was causing mine to cough at idle (sometimes die) and have worse gas mileage. I was back up to 25-26 hiway on my 91 525 before it got wrecked last night with the CTS change. In prior weeks I fixed many vacuum leaks and cleaned the ICV which helped but didn't cure it.
 
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