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Old 04-29-2019, 09:09 PM   #1
fastair
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Gas Mileage

My first 30, 1990 325i, manual with 3.73 lsd. Has new Bosch O2 sensor, new blue water temp sensor, new plugs, rotor, cap, ignition wires. Have not done a smoke test but all vac hoses seem to be in good shape. Car starts good and settles into an idle of around 650 rpm. Overall the engine seems to run good but it seems to be running a little rich. Cannot actually smell raw gasoline but it has a rich smell to the exhaust. I am getting around 19/20 miles to the gallon. How does this compare with what you guys are getting? Thanks
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Old 04-29-2019, 09:11 PM   #2
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Old 04-29-2019, 09:11 PM   #3
e30davie
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M20b23. Megasquirt tuned quite well. Around 22-23mpg
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Old 04-30-2019, 01:23 PM   #4
earthwormjim
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Purely city/town driving, I'm lucky to get 19 mpg.

My typical work commute, which is 80% highway and 20% city, I get 21 mpg at 80mph, and 25-26 mpg at 60-65mph. This is averaging both directions, my commute to work is always 2mpg better than my commute back home.
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Old 04-30-2019, 05:04 PM   #5
dnguyen1963
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My summer is around 26 - 27 mpg. Winter drops down to 24 mpg. It has been like this for a long time.
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Old 04-30-2019, 05:11 PM   #6
ButtJuice
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My gas mileage is probably right around there, SETA bottom with an 885 head. However I only shift when I hit 6k+ RPMs.
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Old 04-30-2019, 06:43 PM   #7
fastair
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Well, I'm not getting that kind of mileage, even though the car seems to be running good. I pulled the dip stick out today while the car was running and the idle got slightly worse, pulled the oil fill cap off and the idle got extremely rough. Any thoughts on what to check to improve my mieage and eliminate the rich smell?
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Old 04-30-2019, 08:02 PM   #8
e30davie
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Note: the crank case on the m20 is part of the vacuum system, by opening the dip stick and oil filter you are letting additional Air into the engine that the ecu doesnt know about = it will run worse. the fact that it does run worse means that the system is working as it should.

Oem m20 ois about as simple of an EFI system as you can get.

yours is a late model, so im pretty sure is motronic 1.3. check the codes as per this:

http://www.unofficialbmw.com/repair_faqs/motronic.html

other things to check,

-AFM - Probably ok, but there are resistances to check n the bentley manual
-Intake air temp sensor (its in the AFM): same as above, check the the resistances against manual - unlikey to give trouble
-water temp sensor, are known to go bad and cause poor running, I personally would check the resistance and make sure its connected properly, for the price though if you dont know its been changed might be worth buying one.
- TPS - make sure its adjusted and operating as it should (known to give trouble, but perhaps not cause your symptoms)
- O2 sensor - people replace these more often than they replace their underpants. I Reckon there are alot of perfectly good o2 sensors in the bin. There are ways to check if it is working as it should as per the bentley. may cause your symptoms though, so its worth looking into.

Vacuum leaks, make sure there is none. Zero. nada.

distributor cap and rotor - can effect fuel economy if really bad. pull appart and inspect. if a bit corroded give them a go with sand paper. if very corroded replace

sparking plugs - ensure gap is correct - if dont know the last time replaced, might be best to get new ones, cheap enough for a set.

Fuel injectors - not much you can DIY here except pull them out and have them cleaned - last resort type stuff as cleaning is expensive.

Fuel pressure - probably not an issue if running rich

If you do all of this you should find your culprit. k go!

Last edited by e30davie; 04-30-2019 at 08:08 PM.
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Old 05-04-2019, 09:14 PM   #9
r-mm
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Im always at bit stumped to why the e30 has such meh highway millage. I got about the same with my 3.2 911 of the same year, same motronic. On an all highway road trip staying mostly below 75 I can almost see 27mpg. That is rare. Mostly my combined / leaning highway ends up 21-24mpg.


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Old 05-04-2019, 09:18 PM   #10
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Gas Mileage

Am I lucky to be reaping in 30 mpg usually. Cruise control managed to clean and get working and at 65mph I can hover at 40mpg for an hour straight on the interstate. Before cruise control I still managed 30mpg++
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Old 05-04-2019, 10:37 PM   #11
dnguyen1963
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Quote:
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Am I lucky to be reaping in 30 mpg usually. Cruise control managed to clean and get working and at 65mph I can hover at 40mpg for an hour straight on the interstate. Before cruise control I still managed 30mpg++
You might be the only guy with an E30 driving at 65 mph here. The only time I see 40 mpg is when I lift my foot off the gas peddle.
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Old 05-04-2019, 10:45 PM   #12
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You might be the only guy with an E30 driving at 65 mph here. The only time I see 40 mpg is when I lift my foot off the gas peddle.


Wow Iím an idiot thanks
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Old 05-05-2019, 05:49 AM   #13
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Quote:
Originally Posted by dnguyen1963 View Post
You might be the only guy driving an automatic M10 E30 here.
Fixed.
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would be in depending on tip slant and tube size
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Old 05-05-2019, 01:56 PM   #14
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Fixed.


But itís not automatic
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Old 05-05-2019, 03:45 PM   #15
dnguyen1963
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Wow Iím an idiot thanks
Can't imagine what your cat is thinking of right after you post this reply.
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