improving mpg on stock m20?

[Bryanlopez325]

So I figure my car needs a little tuneup. Obc says I'm barely making 14.5mpg and ive definitely noticed it's been gulping gas lately. What are somethings I can replace or maybe add in order to save some gas and my wallet?

[Frankus12]

I think this has been asked a few times already, Not much to add from my understanding, just to make sure everything is there and in good condition. new O2 sensor is important, No vacuum leaks, good rubber everywhere, thinner oil, air filter, pumped up tires, i had my injectors ultra sound cleaned when i bought my e30. The car had 160,000 and he said they were pretty much okay to start with. My e brake used to stick, im sure that didnt help with mpg. If you want to save gas, start with your right foot.

[Bryanlopez325]

Thanks man probably should have done alittle more research before I posted this thread lol

[MR 325]

That's terrible MPG. My turbo E30 does about 18mpg...

If you don't know when the following items have been replaced, replace them...
Distributor cap, ignition rotor, spark plugs, fuel filter and oxygen sensor.

Check your air intake boot and your breather hose (valve cover to throttle body) for cracks and replace as needed.

When were the valves adjusted last? If unsure do a valve adjustment along with new valve cover gasket and rocker shaft plugs.

I'm also a fan of Lucas fuel injector cleaner. Throw one of the little bottles in with a full tank.

[808e30325i]

^+1 frankus. Time to calibrate your right foot.

[Cabriolet]

in my mtech2 i would get 11-12 in the city and 26.4 on the freeway. yes every single light is a drag strip.

i would check the O2 and the TPS.

[E30-325iS]

To every thing that has been said above, I would add checking the CTS. It could be sending a wrong reading to the ECU, causing it to think the engine is cold and run rich.
According to the Bentley it should be, 2200 -2700R @ 68F to 300 - 360R @ 176F. Check it at the sensor and at the ECU pin 45.

[DesertBMW]

M20 is not that efficient to begin with, why. Low compression of the engine only 8.8:1, that is horrible. Bank injection, means 3 injectors fire at the same time, fuel sits on the valve before it's time comes.

[poplars]

still the M20B27 has achieved as high as 35MPG highway... how is that inefficient?

[digger]

on a run at 60-70mph i was getting 36MPG with my stroker with old cam and with my current cam 32mpg. this is is as good as the stock engine if not better.
in traffic it all goes to downhill fast id be lucky to get 18-20mpg but that is probably mostly right foot issues

[jlevie]

Getting the engine to run right would be the first priority. At a minimum that would include:

New OE/OEM distributor cap, rotor, and wires, as well as NGKZGR5A plugs.
New OE O2 sensor
Valve adjust
Check engine temperature with a contact or IR thermometer (should be 78-81C)
Check exhaust back pressure to see if the catalytic converter has been damaged by running rich
Check rail fuel pressure and have the injectors cleaned, rebuilt, and flow tested.

Compression (dry & wet) and leak down tests should be done to assess the condition of the rings, cylinders, and valves. An engine with 150k on it will almost always benefit from a valve job, which might require a new cam (get a Cam Doctor report) and may need new guides and exhaust valves. It may not be worth doing much with a high mileage engine (over 200k) if the tests show serious cylinder or ring wear.

Once I have done all I can to improve engine operation I'll put the car on a dyno and get the AFR trace. It should be essentially 14:1 across the entire power band at both full and part throttle. Where deviations occur in the trace will suggest potential causes.

This will increase fuel mileage, and as a bonus the engine will make more power.

[Bryanlopez325]

Thanks dudes this helped, parts should be coming in the mail soon

[CrazyJew89]

So mine has 200K+ miles and it has been abused and neglected for many of them in Michigan. Over time I was able to get it all the way up to 28-29 mpg @80mph. All of the tune up stuff mentioned helped, but the one that I don't see mentioned is the one that helped me the most. Changing the trans and diff fluid to synthetic. This alone gained me a several mpg. Also if you do lots of city driving maybe consider an MSD box. A friend of mine saw 2 mpg city when he added his.

[Q5Quint]

I am going to get theoretical on you.

Scenario:
You are moving a 3000lb car at 60mph down a flat level highway, with zero wind.
How much energy does this take if you account for rolling and wind resistance?

Solution: around 15hp.


If you want more mpg, you need to decrease rolling resistance (pump up your tires, new wheel bearings), decrease wind resistance (easy, just drive slower, or hard, add add splitters and a pan under your car) and make sure your "Engine Brake Specific Fuel Consumption" is as low as possible.... ie your engine is operating in its most efficient rpm at whatever speed you are driving. That means engine tune up and tune in to exactly what your scenario is.

Things like a 2.93 diff might help your highway driving by lowering your cruise rpm and therefore fuel consumption, but it might also make your in-town consumption worse. A 4.10 might make your in town a little better, but your highway worse.

Read about math here: https://physics.ucsd.edu/do-the-math...g-on-gasoline/

and a fun calculator here: http://ecomodder.com/forum/tool-aero...resistance.php

I need to add that pan back to the front of my car apparently.

[CorvallisBMW]

swap in an eta motor