MPG Conundrum!!

[Old'n'Slow]

So....anyone up for a little Sherlock Holmes action?

my happy little eta used to get 30+ MPG... until last November, when it suddenly dropped into the low 20s and has never come back in spite of absolutely babying the gas pedal and changing the following parts(they needed it anyway...)

Fuel hoses
Spark plugs(looked fine)
Dist. cap + rotor
Air filter
Timing belt
Water pump
Coolant
Clutch
Muffler
O2 sensor
New front wheel bearings
Lubed all brake calipers and checked for dragging brakes
Changed to less agressive rubber on my winter bottlecaps
4 wheel alignment... all numbers in the green

None of the above seems to have had the slightest impact.

The odd thing is that gas doesn't seem to be leaking anywhere, and if the injectors were messed up, the plugs would have deposits on them. Power seems fine. I've checked every underhood electrical connection I can find, and the fault code reader is coming up clean.

This all seems to have started after I installed a new clutch, but I can't find a link to the problem from that event. with the rear wheels in the air and the car in neutral, it is easy to spin the drivetrain by hand. I would think it would take an awful lot of drag to take 8-10mpg away!

If an electrical connection failed and the car was running in a cold start condition all the time, wouldn't the plugs be carbon fouled?

Soooo....all you E30 wizards....begin flexing!

[RobertK]

Have you tried actually calculating the MPG yourself? The OBC may not be reading correctly.

If it really is getting bad gas mileage have you tried replacing the engine temp sensor (not the sendor)? I've heard it can may with your A/F mixture if it's malfunctioning.

Also sense you changed your clutch you may not have the flywheel sensor thingies positioned correctly making the OBC readout incorrect. But that's just a guess.

[silversleeper]

I calculated mine and I'm averaging about 16mpg city... and that's when I try to be easy on it, with the occasional spirited driving here and there.

Is that about normal or should I expect to be in the mid 20s?

I miss my R6...

[nando]

could be winter gas. I always notice a drop in fuel economy when it gets colder. a couple weeks ago it was like 13 degrees and I was only gettnig 16mpg, when I normally get about 20.

[Old'n'Slow]

Have you tried actually calculating the MPG yourself? The OBC may not be reading correctly.

If it really is getting bad gas mileage have you tried replacing the engine temp sensor (not the sendor)? I've heard it can may with your A/F mixture if it's malfunctioning.

Also sense you changed your clutch you may not have the flywheel sensor thingies positioned correctly making the OBC readout incorrect. But that's just a guess.

All MPGs are actual calculations of miles driven/gallons at fill-up.

Haven't checked the voltage at the sensor, but that's a good idea...but if the mixture were bad, I would imagine there'd be carbon fouled plugs as evidence...

Oh, and Super etas don't have flywheel sensors.

Silversleeper, you have an "i". Etas are hi mpg rides, but thanks!

Nando, I thought about the winter gas thing, but the previous 4 years I've had the car, winter mileage has been steady- in the high 20's, low 30's.

Still have ??? flying from my cranium...

[TwoJ's]

have you tested your afm? could be messing up your air/fuel mixture.

[browntown]

didnt kencopper have this problem recently. Might not of been him, but I remember a similar post recently. Try the search.

[Scott314]

So....anyone up for a little Sherlock Holmes action?

my happy little eta used to get 30+ MPG... until last November, when it suddenly dropped into the low 20s and has never come back in spite of absolutely babying the gas pedal and changing the following parts(they needed it anyway...)

Fuel hoses
Spark plugs(looked fine)
Dist. cap + rotor
Air filter
Timing belt
Water pump
Coolant
Clutch
Muffler
O2 sensor
New front wheel bearings
Lubed all brake calipers and checked for dragging brakes
Changed to less agressive rubber on my winter bottlecaps
4 wheel alignment... all numbers in the green

None of the above seems to have had the slightest impact.

The odd thing is that gas doesn't seem to be leaking anywhere, and if the injectors were messed up, the plugs would have deposits on them. Power seems fine. I've checked every underhood electrical connection I can find, and the fault code reader is coming up clean.

This all seems to have started after I installed a new clutch, but I can't find a link to the problem from that event. with the rear wheels in the air and the car in neutral, it is easy to spin the drivetrain by hand. I would think it would take an awful lot of drag to take 8-10mpg away!

If an electrical connection failed and the car was running in a cold start condition all the time, wouldn't the plugs be carbon fouled?

Soooo....all you E30 wizards....begin flexing!

Your list above looks pretty good, but did you replace the fuel filter recently? That made a difference for me, although not nearly as drastic as 10 mpg. Also, spark plug wires started to have a negative impact on fuel economy for me the last few months. Now that they've been changed its back to normal.

[KenC]

I'm getting about 4-5 less mpg this winter than I usually do. I'm hoping it's just winter gas + cold weather.

If it doesnt improve in the Summer, I'm going to replace the AFM.

[Old'n'Slow]

OK.

So here's what I figured out.

Somehow, after I did my clutch job, I changed something that now causes my odo to read about 40% low. 1 mile travelled shows up as about .6.

What the hell did I do, and how do I fix it?

[DaveInLA]

My 89 325is (127K miles) gets about 17 mpg in pure city and low 20s in pure hwy driving. I guess that's consistent with EPA estimates when the car was introduced, but I've heard of people with similar cars averaging 25+ mpg. I wonder if there's something wrong with my car. I occasionally drive it hard, but most of the time I shift at 3K.

[abepark]

OK.

So here's what I figured out.

Somehow, after I did my clutch job, I changed something that now causes my odo to read about 40% low. 1 mile travelled shows up as about .6.

What the hell did I do, and how do I fix it?

would changing your diff to a quicker ration do the same thing?

[netcsk]

a clutch job should have nothing to do with it. The reading comes from the rear diff. and no matter what ratio you have, it should always be right (as long as you don't change any drivetrain components to different ratios - including tires/wheels).