M20 horrible fuel economy

[Slicktop_serg]

So i recently got my car running and i am now daily driving it and i noticed my fuel economy is horrible. I changed my O2 sensor and coolant temperature sensor... and it sort of got a lil better but still bad. I haven't changed the fuel filter or spark plugs. but i check the spark plugs and they were black which means mad carbon... sooo any suggestions on what i can do before replacing more things? Please help thank you..

[Gregs///M]

Check for vacuum leaks.

[efficient]

-thermostat to make sure its running at its proper operating temperature.
-fuel filter
-plugs/wires
-cap n rotor

[bmwstudent]

check air filter too

[MR 325]

Sounds like you need to do a FULL tune up. Spark plugs, cap, rotor, valve adjustment, fuel filter, valve cover breather hose, air filter, etc. You should also check the TPS for proper adjustment.

[E30_fiend]

^^^^
On board for all of that. You should probably also change your valve cover gasket during the valve adjustment.

Other than that, the only other thing I can think of is checking your intake boot for cracks. A big unmetered vacuum leak will cause your O2 sensor to switch to its rich limits to protect the motor from damage.


Taylor

[MR 325]

Good point Taylor. Check the condition of the intake boot and idle control valve hose.

[Slicktop_serg]

Thanks guys will check and keep you posted if i need anymore advice/help

[K1CKBAC]

What is your current mpg?

[Slicktop_serg]

obc went from 14mpg to about 23.5 now but im only getting about 150-160 miles on a tank. and im driving conservative. I feel like its just drinking the shit out of it

[Slicktop_serg]

That was after changing the coolant temp sensor

[dnguyen1963]

160 mi per tank? What kind of car do you have? My 325IC get about 24 mpg (@380 mi per tank) overall even with winter tires.

[CabbE30]

obc went from 14mpg to about 23.5 now but im only getting about 150-160 miles on a tank. and im driving conservative. I feel like its just drinking the shit out of it

That's way too thirsty. I agree what everyone else has said about the tune-up. You can also check your afm:

http://www.r3vlimited.com/board/showpost.php?p=2584678&postcount=1

[jlevie]

You don't say if the car has an M20B27 or M20B25 engine, but for the most part the actions will be the same:

1) Replace the distributor, ignition wires, and install a fresh set of NGK ZGR5A plugs.
2) Replace the O2 sensor
3) Adjust the valves
4) Check engine operating temperature with a contact or IR thermometer (should 80C)
5) Verify that the ECT signal as measured at the DME is correct
6) Check rail fuel pressure
7) Have a smoke test run and fix any leaks
8) If the cover of the AFM shows it to have been removed, replace the AFM.
9) Have the injectors cleaned, rebuilt, and flow tested
10) Have a back pressure check run to see if the catalytic converter is clogged, replace if indicated.

If the problem persists the next actions would be to:

1) Get dry and wet compression numbers and hot leak down numbers
2) Put the car on a dyno and get AFR curves for part and full throttle operation

What to do then would depend on what those results are.

[harold30]

You don't say if the car has an M20B27 or M20B25 engine, but for the most part the actions will be the same:

1) Replace the distributor, ignition wires, and install a fresh set of NGK ZGR5A plugs.
2) Replace the O2 sensor
3) Adjust the valves
4) Check engine operating temperature with a contact or IR thermometer (should 80C)
5) Verify that the ECT signal as measured at the DME is correct
6) Check rail fuel pressure
7) Have a smoke test run and fix any leaks
8) If the cover of the AFM shows it to have been removed, replace the AFM.
9) Have the injectors cleaned, rebuilt, and flow tested
10) Have a back pressure check run to see if the catalytic converter is clogged, replace if indicated.

If the problem persists the next actions would be to:

1) Get dry and wet compression numbers and hot leak down numbers
2) Put the car on a dyno and get AFR curves for part and full throttle operation

What to do then would depend on what those results are.

I have the same problem. I have replace almost all of the above list aside from distributor, rotor and valve adjustments that I'll do next. But before hand, is there any signs that the distributor and rotor needs to be replaced?

Thanks...