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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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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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:
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, 08:08 PM.
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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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Originally posted by Sonny View PostAm 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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