horrible gas milage

[mikeinaus]

my car gets horrible gas milage. ive done almost everything (including an engine swap) you can think of and it still sucks. im getting about 250km to 40/45L of gas. ive tried different octanes and different brands and nothing seems to really help. if i drive like a complete Pansy i can get maybe 250km-30L. what can affect gas milage this bad?

engine seems to run fine, no noticeable lag when accelerating, it doesn't choke, and it idles strong at 600rpm.

i have no dead cylinders, engine doesnt shake or make any odd noises
o2 sensors were replaced 3 tanks-750km ago without much help
doesnt noticeably burn oil
brakes are not stuck on or dragging
tires are full of air
rear wheel bearings were replaced a few months ago
new fuel filter in may
new plugs in may
new fuel screen/pump last month


the only code im getting is for the egr. can egr affect my milage this bad? i also have a big exhaust leak before my muffler if that could make a difference?

[Sleeper6]

Egr can mess up your mileage pretty bad atleast on most gms Ive worked on, never seen a dead one on an mx3 tho. Otherwise you might want to try a K&N, synthetic oils, and stick with a top octane and a light foot. I run this way +my cat back and I can pull 32-34mpg if I drive like grandma. But it does drop to about 25mpg if I run it hard. Oh and an exhaust leak at the muffler shouldnt hurt you at all.

[Newfie_dan]

The exhaust leak can indeed hurt mileage as it kills the torque of the engine due to the loss of backpressure. The same applies for a big exhaust on any small displacement engine. You need some backpressure and although you can gain some hp by putting in a higher flowing exhaust they still retain some backpressure. Egr can also mess up fuel mileage pretty bad but fuel mileage is also highly dependant on idle time, driving habits/style, and mechanical condition of an engine and wheels/wheel alignment. Bigger/wider tires will affect fuel mileage due to the increase in friction as well as the alignment of those wheels. I get pretty crappy mileage if I use my remote starter every day to warm the car up to the extent of almost getting the 250ish kms to a tank. If I just drive it without using the remote start that jumps to about 400/tank. I have gotten that egr code a few times at random intervals and I am going to attend to it next weekend by cleaning the egr valve out.

[mikeinaus]

i have a weapon r cone filter, and im using penzoil platnum synthetic. 94 octane seems to run slightly worse then 89 so ive just been using that. i dont know if my egr is dead but it turns on my cel randomly. very rarely my idle will also raise for no apparent reason, its gone as high as 2500rpm at stop lights.

my alignment is off, my car pulls to the right pretty bad, ive just been putting it off for way to long.

maybe its a combination of everything? egr, exhaust and alignment?

ive got a new 2.25" high flow exhaust, im just waiting to get it welded and installed.

how hard is it to clean out the egr? maybe i should give that a go at some point.

[Newfie_dan]

clean out the egr valve and go from there. Any noticeable tire wear on the front tires at all?

[mikeinaus]

they are wearing down a bit. i think thats mostly cuz they have almost no grip in the rain and i peel out alot because its rains like every day here.

[Newfie_dan]

well if you are doing jack rabbit starts a lot then that will kill a lot of your gas mileage there. tire wear and alignement play big factors in fuel mileage as well. Any noticeable pull left or right if you let go of the wheel on a straight level road?

[mikeinaus]

yeah it pulls pretty hard to the right. ill get my exhaust welded and an alignment done next weekend. thanks for the tips. hopefully they help...

[Newfie_dan]

no problem man if ya need any more help just lemme know.

[RX8SE3P]

Yep get an alignment for sure, just for starters and see how much improvement you get. Then if you need better mileage, try some of the other suggested alternatives.

[wytbishop]

My car has always gotten 370-400 on 40L or so of fuel. Before and after the ZE swap. It's always frustrated me because I see no reason for it. It could be related to the EGR. I have my EGR valve in place but it's not connected to the exhaust. I will block it off properly at some point, but I dont' see how that could be causing me a problem. I am a little suspicious of my TB. Not for any reason in particular, but it's the only thing I can think of that's a likely cause.

I'm totally stumped on mine. I hope you have better luck with yours.

[Sleeper6]

well if you are doing jack rabbit starts a lot then that will kill a lot of your gas mileage there. tire wear and alignement play big factors in fuel mileage as well. Any noticeable pull left or right if you let go of the wheel on a straight level road?

Gonna have to agree here, driving like that is going to kill your mileage and you left out the whole alignment bit, both will hurt you in the long run.

[davmac]

250 km / 40 l = 14.7 mpg = Agree this is horrible. Something definitely wrong here.
400 km / 40 l = 23.5 mpg = Not great, but easily explained if nearly all stop and go city driving and / or cold outside

When it is cold it takes lots longer to get efficiency of engine at operating temperature. Also it does not take much idling to shoot your mileage since for that time you get 0 km / l.

[Tollis]

Especially if you run cold air intakes during the cold months takes even longer to get to efficent tempatures.

[Newfie_dan]

Yeah colder weather will kill mileage for sure, I am putting a winter front on mine next winter as the temps here drop pretty darn low and wind chill is killer. Egr does impact mileage if the engine was designed for it there has been a big debate on wheter or not egr impacts engine performance/mileage and I don't like the idea of egr solely because its dirty left over crap being fed back into the engine, if it were filtered I would like it more but I have seen egr cause as many problems as it has benefits. No matter how clean your engine burns egr is plain out dirty.