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Old 11-20-2013, 09:44 AM   #1
Lps5053
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What could be causing my bad gas mileage?

Right now, according to the OBC, I am averaging 21.1 mpg. I feel that this is extremely low for my style of driving. Now, because it has been cold, I've been staying out of 5th gear on short commutes but even on the highway going 65, on flat ground, the car is reading below 20mpg on the instant reader and I am only giving it enough throttle to keep it steady at 65mph. Basically my question is, would a faulty or dying intake camshaft position sensor cause worse gas mileage. I was averaging 25-27 when I first bought the car but have been steadily declining since.

I already replaced my DISA (which was faulty) but I still get random acceleration episodes where the car just takes off on its on. It acts like I am putting my foot down to the floor but I am lightly accelerating through gears. My mechanic said that could be due to the intake cam pos sensor but want to get your guys opinions before I throw more money at the problem just to find out it's not fixed.
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Old 11-20-2013, 09:55 AM   #2
Lps5053
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Car is an 01 330ci. Only code is clutch circuit switch which is why my cruise control doesn't work.
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Old 11-20-2013, 09:58 AM   #3
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Check your operating temperature when the car has supposedly warmed up.

It should be 93-96C. If you are in the 80's, you have a soft failing thermostat.

Paging jfoj.
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Old 11-20-2013, 10:00 AM   #4
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Always the first thing to check is the engine coolant temperature.

Forget your gauge, it is a joke, not accurate unless you reprogram it.

Read the 3rd link below in my signature. Very likely you need a thermostat.

Once you have eliminated/repaired the engine coolant temp, then we will move on from there.
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temps, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose fan switch O-ring - BMW #13621743299
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Old 11-20-2013, 10:00 AM   #5
jfoj
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AC, I was typing as you posted!

OP, also check your tires, for every 10F drop in temp, the tire pressure drops by 1 PSI. Remember 10F=1 PSI either direction.
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temps, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose fan switch O-ring - BMW #13621743299

Last edited by jfoj; 11-20-2013 at 10:01 AM.
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Old 11-20-2013, 10:38 AM   #6
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I sure hope you aren't relating tire pressure to coolant temp but rather ambient.
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Old 11-20-2013, 10:47 AM   #7
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I sure hope you aren't relating tire pressure to coolant temp but rather ambient.
Why? My tires are nearly flat during a morning cold start.

I have to wait about 10 minutes for the coolant to circulate in them before they're up to pressure and driveable.





























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Old 11-20-2013, 11:00 AM   #8
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You scared me for a minute there
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Old 11-20-2013, 12:40 PM   #9
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what's the maintenance history?
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Old 11-20-2013, 05:36 PM   #10
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what's the maintenance history?
Off the top of my head I've done DISA, cleaned throttle body, maf all the basic stuff.

Something I found today was that the top part of my air box was half off. Not where it clips and attaches to the base but the "hat" part. It was half off and I'm thinking this could cause some problems.
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Old 11-20-2013, 06:02 PM   #11
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Originally Posted by Lps5053 View Post
Something I found today was that the top part of my air box was half off. Not where it clips and attaches to the base but the "hat" part. It was half off and I'm thinking this could cause some problems.
Not likely causing issues, you NEED to verify your engine operating temperature. A cool running engine will tank fuel economy in no time.

The Hidden OBC Menu will bring the engine temp up directly on the dashboard OBC, again forget the temp gauge, it is always as 12 o'clock.
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temps, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose fan switch O-ring - BMW #13621743299
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Old 11-20-2013, 06:11 PM   #12
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My OBC reading dropped from about 22.9 to 21.5 since summer time. Car runs fine. I'm writing it off to the winter gas.
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Old 11-20-2013, 06:20 PM   #13
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No faulty engine components can cause that much of fuel efficiency SNAFU in such short time.
First thing to check is power delivery rather than power generation. Tire pressure is very first thing to check.

By the way, when did you buy your car? You said it was 25-27mpg average when you bought it, and steadily decreasing ever since.
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Old 11-21-2013, 07:56 AM   #14
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Bought the car in May with 80k miles. Now has 87k. Steady drop in mpg's.

Ran the tests this morning. After a 10-15 minute drive. Current outside temp is low to mid 30's.

Coolant temp: 094

Did these next tests with my obd II read live scan. Not sure if they're pertinent but thought I'd post them.

Engine rpm at idle: 851-877 with the average being 855-860
IAT degrees Celsius- 25
MAF (g/s)- 4.34

Fixed the airbox last night and after that idle rpm went from 500-600 (somewhere in that range) up the 850ish that they are now.
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Old 11-21-2013, 08:08 AM   #15
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94C is in the proper range.

Mentally average this and make sure it holds while cruising on the highway.

94-96C tends to be the baseline engine temp on these cars.

Then check the Long Term Fuel Trim values at warm idle and report back what they are.

Cam sensors do get soft and sloppy without triggering any codes.

Also verify your engine temps and are you allowing the car to warm up for extended periods now that is has cooled off?

My daughter jumped on me about her mileage dropping recently, but she drives about 1 mile to school in the morning and between Winter fuel blends, short drives and cooler ambients mileage will drop off a bit anyway. Again, as the ambient drops each 10F, tire pressures drop 1 PSI.
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temps, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose fan switch O-ring - BMW #13621743299
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Old 11-21-2013, 08:43 AM   #16
Lps5053
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Originally Posted by jfoj View Post
94C is in the proper range.

Mentally average this and make sure it holds while cruising on the highway.

94-96C tends to be the baseline engine temp on these cars.

Then check the Long Term Fuel Trim values at warm idle and report back what they are.

Cam sensors do get soft and sloppy without triggering any codes.

Also verify your engine temps and are you allowing the car to warm up for extended periods now that is has cooled off?

My daughter jumped on me about her mileage dropping recently, but she drives about 1 mile to school in the morning and between Winter fuel blends, short drives and cooler ambients mileage will drop off a bit anyway. Again, as the ambient drops each 10F, tire pressures drop 1 PSI.
My drive to work is a short 5 miles if that, driving conservatively and stopping at dunkin will put me at about 15 minutes from the time I leave my house until I get to my shop. I guess it is very possible that my drop is due to not driving much more then other then the occasional trip to pick up/ drop off a customer car. I'll definitely check the tire pressure today.

I ordered a new intake cam position sensor that will be here Saturday and I'm hoping that will fix my random acceleration problem and maybe help with my gas mileage even though I have yet to have a code for it.
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Old 11-21-2013, 09:18 AM   #17
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Remember that engines use far more fuel at idle and when the car is idling and not moving your MPG=0.

Also there is the cold start fuel enrichment and as the engine is cold it runs richer until fully warmed up.

If you are in the drive thru or leave the car running at Dunkin, then MPG=0.

The way to solve this problem is to just do a 30-60 minute highway run and fill up at the start and the end of the highway run. Then manually calculate your findings.
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temps, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose fan switch O-ring - BMW #13621743299
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Old 11-21-2013, 10:33 AM   #18
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Been following this thread as well as I think my car could do better than the 21.5 average over the last few months. Checked my temp with the hidden OBC last night and it got to 92-94 quickly and stayed there, in town and at 60mph on the highway. Dipped to 88 when I turned the heater on but quickly went back to 94.

Going to check the DISA, would that have a big effect? Is 21.5 average for these cars in the winter? My wife drives it 28 miles one way commute everyday. About 10 miles of town-ish driving and 20 miles on the freeway at 65-70mph. Her return commute can involve some stop and go which I know doesn't help. Should she be doing better on mpg or is that par for the course with a 330ci?
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Old 11-21-2013, 06:15 PM   #19
Lps5053
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Been following this thread as well as I think my car could do better than the 21.5 average over the last few months. Checked my temp with the hidden OBC last night and it got to 92-94 quickly and stayed there, in town and at 60mph on the highway. Dipped to 88 when I turned the heater on but quickly went back to 94.

Going to check the DISA, would that have a big effect? Is 21.5 average for these cars in the winter? My wife drives it 28 miles one way commute everyday. About 10 miles of town-ish driving and 20 miles on the freeway at 65-70mph. Her return commute can involve some stop and go which I know doesn't help. Should she be doing better on mpg or is that par for the course with a 330ci?
My dad's 330i is getting about 21.5mpg on his short commute to work so I'm starting to think that maybe this is just how it will be. I replaced the DISA because I had a code for it and I have a random acceleration problem that I was hoping the DISA would fix. It did not but did restore some power. Hoping that when the new camshaft position sensor gets here over the weekend, I'll at the very least lose my random acceleration and hopefully gain back a couple mpgs in the process.

I very seldom leave my car and leave it running. I don't live in a bad area but don't want to chance it.
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Old 11-21-2013, 06:28 PM   #20
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Stop and go driving will quickly lower the average, low 20s isn't bad.
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