bad gas mileage

[jdbmw325is]

hello ever one i resently bought a 1989 325is off my friend. just a list of new parts to better help with diagnosing the problem im having.

bran new head
new injectors
new fuel rail
new hoses
new water pump
new timing belt
new radiator
new thermostat
new fuel filter
new O2 sensor
and cleaned intake and exhaust manifolds

most of the top part of the motor have be replaced. the problem is im getting about 10 miles per gallon plus my check engine light is no. i filled the tank up and got about 160 miles befor it was close to the refill mark. the digital MPG estimator tells me im getting 10.0 even when im on the interstate and the analog MPG estimator on the gauge cluster reads about 25 MPG. also when the engine is cold it acts a little funny. the tach will wander between 500 and 1000 RPM's. then after a bit it will tach to about 2000. it will do this untill the engine temp is above the blue line on my temp gauge, then it will runn nice and smooth around 900 to 1000 RPM's. also when the car is running it smells rich.

[wafflesburger]

hello ever one i resently bought a 1989 325is off my friend. just a list of new parts to better help with diagnosing the problem im having.

bran new head
new injectors
new fuel rail
new hoses
new water pump
new timing belt
new radiator
new thermostat
new fuel filter
new O2 sensor
and cleaned intake and exhaust manifolds

most of the top part of the motor have be replaced. the problem is im getting about 10 miles per gallon plus my check engine light is no. i filled the tank up and got about 160 miles befor it was close to the refill mark. the digital MPG estimator tells me im getting 10.0 even when im on the interstate and the analog MPG estimator on the gauge cluster reads about 25 MPG. also when the engine is cold it acts a little funny. the tach will wander between 500 and 1000 RPM's. then after a bit it will tach to about 2000. it will do this untill the engine temp is above the blue line on my temp gauge, then it will runn nice and smooth around 900 to 1000 RPM's. also when the car is running it smells rich.

Why don't you read the engine code?

[jlevie]

The econometer in the cluster is driven by the on time of the fuel injectors. Around 25 would be about right for cruising at highway speed. That could imply that the fuel pressure is excessive or that you are leaking fuel when driving. The Bentley manual has a suite of fuel system tests that will reveal any problems with the fuel system. Those tests should be the first action in diagnosing this problem.

[jdbmw325is]

it was good advice to get the code read. ended up i had a engine coolant temp sensor that was bad. my motor thought the engines was cold even when it was at full operating temp. it has made my car run much soother. im still not getting great gas mileage though. the digital estimator reads about 12 or 13. how acurate are they? im wondering if not having a catalytic converter would cause this? the shop confirmed that the O2 reading is not corect due to not having a cat.

[jlevie]

The O2 sensor si before the catalytic converter. So it will produce the same data w/wo a catalytic converter. If you are getting invalid data from the O2 sensor and no other faults, the sensor needs to be replaced.

[BlUe E30]

i thought the econometer on the dash under the tach was driven off of vacuum? the digital ones are not always accurate the best way to find out what you are really getting is go from full to empty and divide the milage by the gallons used. do that a couple of times and get your average. and OBD1 the shop people are idiots its only a pre cat O2 sensor like jlevie said. did you put all stock parts back into the head or upgraded? I have upgraded parts and mine runs great but i still get 12-15 to the gallon in town. (also check with your right foot to see if he knows anything about your problem)