Terrible MPG

[surechap]

1997 318ti Automatic

Update: I still have terrible gas mileage latest number was 19 mpg 65/35 City and Highway
Changed intake boot/bellows
Changed both o2 sensors.
Changed the temperature coolant sensor.
Added Redline fuel system cleaner.
Tire pressure checked.
Valve cover job, new spark plugs, new spark plug tube seals.
Oil changed.
Air Filter changed.
Thermostat change, coolant flush, coolant bleed.


Items Checked:
MAF sensor checked, I unpluged it while the car was running. The idle changed and in one case the car completely died. Cars MAF sensor is working fine.

Also cleaned MAF


Issues:
Thermostat goes past the middle slightly only sometimes?

What is this black stuff that is on the underside of the air filter cover? It's going straight to the engine without being filter and its crumbling how to I replace it?

[bmwconnect]

Originally Posted by surechap

Is the secondary air pump suppose to turn on everytime you start the car? Even in freezing winter? I'm getting 15 mpg, I redid the valve covers and changed the sparkplug tube seals, new air filter, new oil filter everything. WTF sorry, very frustrating.

What about the O2 sensor?

[surechap]

I'd like to add that my car also exibits these other symptoms:

Car has trouble heating, even at full blast and the temp set to maximum. The car will get warm, but not hot.

Trouble starting ONLY when warm, if I turn off the car and immediately try to restart the car it will stuggle. It's also not a smooth start, the car will go booop boop boop then start. As described here.
http://www.318ti.org/forum/showthread.php?t=37748

I also experience vibrations in the car, once the car is warmed up its not as severe as described here.
http://www.318ti.org/forum/showthread.php?t=37705

[ion_four]

Mileage does tend to drop SIGNIFICANTLY when the ambient temperature drops (tire pressure drops, higher rolling resistance from harder tire rubber, higher wind resistance due to more dense air...)

That being said, I would suggest checking the thermostat. I have only had my ti for a few months, but the mileage has also dropped for me as the weather has gotten colder, and I suspect the thermostat is not fully closing, as it seems to take a while to get good heat. I just haven't had the chance to fix it...

[stock]

I had that problem last week. Changed the thermostat and miles per gallon increased significantly. Have a bunch more heat in the car too.

symptoms were when moving at freeway speeds, temp gauge would drop to the colder end. Needle would move up and down depending on load. Now whatever condition or temp, needles dead center.

could also need a good coolant system bleed, but thermostat is so cheap and easy to replace.

[surechap]

The latest number was 19.5 mpg. Any ideas? I've updated some changes I've done on my very first post.

[jenkinskg]

Just got my TI, going through and changing all plastics in cooling system
Also thermostat and housing
Then going waterless
http://www.amazon.com/Evans-NPG-Cool...ess+antifreeze

[SSpeedracer]

That's horrible mileage.

What did the spark plugs look like? black/wet? All the same?

It might not even be the engine:
What RPM at speed? Is the trans up shifting?
Do the wheels spin freely? Bad bearing or brake caliper dragging?

Also, if the DISA is left open at lower RPM's the runner length is shortened and less efficient fuel mixing. A bad vacuum line would leave DISA open but it shouldn't kill off your mileage that much.

Lastly, don't take this the wrong way, but you're measuring mileage by odometer/gallons at each tank fill up topped off right? Not an aftermarket OBD computer.

[jenkinskg]

Just changed my thermostat and rear head pipe on my 1997 318 ti
Then I filled it with Evans NPG
Runs nice at 210 Deg F
Mileage went way up
At full temp I can open it and look at the level, been running for 2 weeks now and works really great!

[jenkinskg]

While mine was apart found the inside of the airbox filled with old foam rubber about to crumble and get sucked into engine
Took it all out and cleaned with shop van then washed with water
Will change over to a pod K&N type filter soon

[surechap]

Originally Posted by jenkinskg

Just changed my thermostat and rear head pipe on my 1997 318 ti
Then I filled it with Evans NPG
Runs nice at 210 Deg F
Mileage went way up
At full temp I can open it and look at the level, been running for 2 weeks now and works really great!

You think it could be the thermostat? I just did the whole coolant bleed/flush and thermostat change about 3 months ago. Along with the new temperature sensor. I admit I probably didn't bleed the system right, but it shouldn't cause that much of a difference right? Every time I drive my car from cold start the cars computer puts the rpm at past 3k to heat up the engine, thought that was normal. I also wanted to add it's spring now and my car still eats gas temperatures averaging 70+ degrees.

Yeah, I really need to clean the air filter the crumbling foam is everywhere, but I don't think that would cause mpg to hurt that much the airflow is correct just dirty air.

[surechap]

Originally Posted by SSpeedracer

That's horrible mileage.

What did the spark plugs look like? black/wet? All the same?

It might not even be the engine:
What RPM at speed? Is the trans up shifting?
Do the wheels spin freely? Bad bearing or brake caliper dragging?

Also, if the DISA is left open at lower RPM's the runner length is shortened and less efficient fuel mixing. A bad vacuum line would leave DISA open but it shouldn't kill off your mileage that much.

Lastly, don't take this the wrong way, but you're measuring mileage by odometer/gallons at each tank fill up topped off right? Not an aftermarket OBD computer.

I'm not sure if the transmission is going bad, but when I was at a drive through for a really long time I notice the cars power significantly degrade. I had really hard time getting to speed and really needed to gas it. I remember reading the manual saying it's not good to leave the car idle for long and you should rev the engine past 3K for about 10 minutes. So I put my car into lower gear "3" for the automatic and drove home at a little past 3k for 10-15 minutes, that was about 2 weeks ago. The car acted a little funny and over the course of two weeks the power seems to return to normal, not sure if this is placebo.

My car does feel like somethings holding it back: brakes/calibers, but I keep thinking it's just the 4 cylinders. I haven't had time to look at it as I'm really trying hard to graduate.

I remember 2 or 3 of the spark plugs were soaked in oil when I did the valve cover job. I really don't want to check the spark plugs again, because I'm scared to strip the threads BMW uses kind of high torque specs.

Yes, the mileage is always checked properly my calculations say 19.5 OBC 20.9. I decided to not reset my OBC this time and just drive off surprisingly the OBC mileage improved it's now 21.1. This is really frustrating indeed can't seem to pinpoint the problem.

[SSpeedracer]

Originally Posted by surechap

My car does feel like somethings holding it back: brakes/calibers, but I keep thinking it's just the 4 cylinders. I haven't had time to look at it as I'm really trying hard to graduate.

Jack up each tire and spin it by hand. You'll know if something is dragging. Or, stop at the top of a slight downhill grade and see if rolls on its own in neutral.

Originally Posted by surechap

I remember 2 or 3 of the spark plugs were soaked in oil when I did the valve cover job. I really don't want to check the spark plugs again, because I'm scared to strip the threads BMW uses kind of high torque specs.

That was leaking motor oil. Your valve cover job fixed that no doubt. Always use antiseaze, particullarly on an aluminum head. If you find the time to pull the plugs, check them for signs of rich/lean fuel. There are pictures on the internet to show you what to look for. And don't torque them so much if you think they will strip. Its easier to tighten a loose plug than helicoil a thread or swap heads.

Originally Posted by surechap

You think it could be the thermostat? Every time I drive my car from cold start the cars computer puts the rpm at past 3k to heat up the engine, thought that was normal. I also wanted to add it's spring now and my car still eats gas temperatures averaging 70+ degrees. Yeah, I really need to clean the air filter the crumbling foam is everywhere, but I don't think that would cause mpg to hurt that much the airflow is correct just dirty air.

A bad thermostat would not degrade mileage by 30%. You should see closer to 28-30 mpg. I don't think the car revs 3k to warm up the engine in 70deg ambient weather. Something is wrong there and I would guess a vacuum leak. What does your car idle at after it is warm? (maybe someone can chime in if there is an incoming air temp sensor that could cause this) At 75 mph you should see ~3100 rpm on tac if the transmission is shifting to 4th gear.