Bad gas mileage

[Hypr5]

Yes, thanks for the advice. I have done this and it did make a bit of a difference. I guess I'm down to checking out the links from the box, but I have a bad feeling the play is coming from the box since I can feel the play with the car off.

[Hypr5]

unless you have leaks in the intake system. check that again extra careful, I had a leak on the bottom side by the intake manifold on mine that took me a while to find in my haste.

Thanks for that, I'll check for leaks real close later on. Will they affect gas mileage too, though? Would a temp sensor throw a code? I'll swap my o2 sensor with a buddy's tonight and let you know how that goes.

much appreciated!

[Hypr5]

A bit late, but heres the followup:

I got a brand new o2 sensor installed and it has increased gas mileage by a whopping 1mpg, I'm just barely above 14mpg now (14.2 or so)

The engine runs a bit smoother, but still has some vibration on the pedal around 1800rpm. Still feels slow as a slug and EATS gas like nothing. 4 gallons got me 30 miles. even though the OBC says 14.2mpg

Any other things I should check? I have no codes, free of vacuum leaks, new o2 sensor, new spark plugs...

Could anything in the ignition system be a culprit?

Thanks a bunch, again.

[Interceptor]

I got a brand new o2 sensor installed and it has increased gas mileage by a whopping 1mpg, I'm just barely above 14mpg now (14.2 or so)

The engine runs a bit smoother, but still has some vibration on the pedal around 1800rpm. Still feels slow as a slug and EATS gas like nothing. 4 gallons got me 30 miles. even though the OBC says 14.2mpg

Any other things I should check? I have no codes, free of vacuum leaks, new o2 sensor, new spark plugs...

Could anything in the ignition system be a culprit?

Thanks a bunch, again.

I have late '91 525i and have the same crappy city consumption! The difference is that my engine runs pretty smooth, no matter if it's hot or cold. I do notice better performance during the cold days, but that's logical. I presume that I have a hole somewhere in the exhaust pipe, near the catalytic converter (the smell of exhaust is noticeable with windows and/or roof window open) - maybe it's possible that it interferes with my O2 sensor in some way? I tried resetting the Motronic and it didn't make a difference. If you do find a solution, let me know! PLEASE!

P.S. Have you considered cleaning the injectors? Also, how much oil it consumes? Mine drinks 1 liter per 1000 miles!

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Regards

[GS535i]

As Interceptor noted in a 'PS' above, Injectors would be my first call. You can try the 'add to the tank' formulation cleaners, of which Chevron Techron is very good; however, these things are best at keeping a system clean, not cleaning one up.
Consider having a "motor Vac" done, or whatever it's called in your area. A fuel system cleaning device is tied into the fuel supply & return lines, and provides a fuel/super detergent cocktail for your engine to run on for ~30-40 min: can do a fantastic job of cleaning fuel rails/injectors/etc.
If that shows promise, also change the fuel filter.
The alternative is to pull and clean the injectors.

[Hypr5]

Mine has almost zero oil consumption and I have run a few bottles of injector cleaner through with no results. I'll keep searching for a solution and keep you updated on anything I hear

About the "motor vac" thing, how much should I expect to pay for one? Is pulling the injectors a big task? I'm sure I can figure out how, I just want to get a rough idea of how long my car will be down.

I appreciate the help guys.

[Bill R.]

guessing that you have the m20 motor? I would check the cap and rotor and plug wires first off, then adjust the valves, clean the Idle control valve
Check the fuel pressure and fuel pressure regulator. One of the things i would strongly suspect is the temperature sensor on the engine. I would check the gap on the crankshaft sensor and set it to the correct specs. Check the air filter. Set the tire pressure up to the correct specs, Check to make sure that no brakes are dragging. Make sure that you're not using ethanol blended or mtbe blended gas which will drop your mileage by an average of 10% or more. Check the coil output to make sure you have a good strong spark. Run a can of bg44k injector cleaner through if you still suspect injectors. Change to a fuel saving oil such as mobil one synthetic 0w30 if you're trying everything you can think of to improve the mileage.
Check the front wheel bearings for excessive drag, check the alignment on the front end, improper alignment will have an effect on mileage and last but not least I would think about replacing that o2 sensor even though your test indicates that its working...










QUOTE=Hypr5]Mine has almost zero oil consumption and I have run a few bottles of injector cleaner through with no results. I'll keep searching for a solution and keep you updated on anything I hear

About the "motor vac" thing, how much should I expect to pay for one? Is pulling the injectors a big task? I'm sure I can figure out how, I just want to get a rough idea of how long my car will be down.

I appreciate the help guys.[/QUOTE]

[Hypr5]

Air filter, fuel filter are new, ICV is freshly cleaned, Finally broke down and bought a brand new o2 sensor. New spark plugs, too.

I'll try a new dist. cap and rotor next. How do I go about testing the coil and fuel pressure regulator, though?

I might be getting somewhere

edit: Yes, m20.. sorry

[Bill R.]

fuel pressure gauge in line where the fuel line connects to the injectors with a t fitting. then you check the pressure with it running and disconnect the vacum line that connects to the fuel pressure regulator, there should a an increase in pressure when you do this. if no change then the pressure regulator is not working correctly.. this is an unlikely possibility however. I would first just check the pressure to make sure you have adequate fuel pressure. The fpr test is easy enough to do once you have a fuel pressure gauge hooked up. The reason i mention the icv is because you mention the rpm dropping to 250 and then slowly rising when you put it into gear cold.. the icv is responsible for keeping the rpm up when you do sudded loads like this and if its responding slowly that will cause this. If you have the valves adjusted incorrectly it will also have a substantial effect on mileage. and if anybody has tinkered with the afm it could also have negative effects on mileage. Most of the m20 525's i see here get around 18 mpg city but traffic can move fairly briskly here without a lot of stop and go....

Air filter, fuel filter are new, ICV is freshly cleaned, Finally broke down and bought a brand new o2 sensor. New spark plugs, too.

I'll try a new dist. cap and rotor next. How do I go about testing the coil and fuel pressure regulator, though?

I might be getting somewhere

edit: Yes, m20.. sorry

[Karl]

I'm with you on this one--start by checking for vacuum leak. Then check temp sensor.