Hi... I was wondering what kind of fuel consumption should I be getting from my 2006 S40 2.4i. This car is new to me and I just got to drive it after a few major repairs. For the most part I filled it up to 14 gallons but only got 275 miles out of it. 75% highway driving. I took it easy on the car, and I think I should be getting a bit more out of it don't you think?

Thanks

 

That seems low, but there are SO many variables, including the definition of "highway driving" and "around-town" driving. I seem to get right around 20mpg "around town", but live in the flat(ish) Phoenix east valley, and a lot of that driving is on freeways with a 65mph speed limit. On a recent 7,000 mile road trip (probably 80% true highway miles) I got right at 28mpg, and just under 29mpg on the highway legs only (yes, I kept the gas receipts and entered them all into a spreadsheet). That's really pretty impressive given that "it's a wagon", "it's an automatic", and that I probably averaged around 80mph on the highway legs (lots of 75- and 80mph speed limits out west and across Texas).

OTOH, the apogee of my trip is Manhattan, where I'd be thrilled beyond words to get 20mpg (most of which is driving around my daughter's hilly north Manhattan neighborhood looking for a parking place (aka "unicorn"). ;-)

And there's the issue of driving style. My wife consistently gets much lower mileage than I do, driving the same car in the same area. She's not got a lead foot, but just isn't quite as smooth as I am.

If your mileage is lower than it should be, the first place to look is at the low-hanging fruit. Put in a new air cleaner element "just because". Even if that only improves your mileage a tiny bit, it'll pay for itself in no time. Check the operation of your PCV valve / system (read up on that to see how). Maybe run a can of fuel injector cleaner through the tank (I personally like Seafoam, but don't put too much faith in many claims of many of the cleaners). And of course, it can't hurt to consider new spark plugs - if it's been a while (as in 50,000 miles) it's another low cost / high return maintenance item.

 

 

You should be getting 25 or more with 75% highway in the flatlands. Do you notice any reduced power or misfires say when accellerating to highway speeds?

When my son mentioned our 2000 S40 was getting poor mileage I replaced the plugs, coil packs and the wire harness to the coils and that got the car back to full power and 25+ MPG.

You should check/replace the air filter (aka the "air cleaner element" is inside the clip covers on the intake box) but I'd be surprised if you had a bad injector without some other symptoms ie one plug that keeps fouling, long cold starts, misfires etc. Any other symptoms? You may need to do some other investigations like testing for fuel pressure, engine compression if there's no other symptoms.

 

So today I took the car in for an alignment and on my way back my check engine light started to blink.. I knew right away that I had a misfire on one of the cylinders. Turned out to be misfire on cylinder 3. I replaced the coil and all looks to be good now. The spark plugs and the air filter have been replaced about two weeks ago. The only symptom I have is rough idle... It just idle's rough. It should be right at 800 rpm but mine is between 600 and 750 what it seems.

We did a smoke test and came back negative. The weird thing is that on cold startup the RPM are right at 800 all the way until you touch the throttle. If i just gently tap the throttle the RPM's will fall bellow 500 and the car almost stalls. Other then that I have no other symptoms.. So I could have 4 more coils going out but I cant test that unless I just get 4 new ones. If one has failed others are to come sooo...

 

 

I've gotten pretty horrible mileage driving through St. Louis... yes, the traffic can run pretty well, but it's a whole lotta stop and then go and stop and go and stop and go. ;-) (I grew up 45 miles east of there and my sister lives in Creve Coeur).

Getting around 26mpg isn't really bad - could be better but it's "close enough" that it's going to be hard to find a really black-and-white symptom to fix.

One thing I've done in the past (often without any tangible results) is to replace the upstream (pre-cat) O2 sensor, which is the one that tells the engine management computer how much fuel to squirt into each cylinder. If it gets dirty / worn, it can start mis-reporting and cause efficiency issues. They are suspect over 100,000 miles, though they don't fail entirely very often.

 

Lucky for me I work an earlier shift which means I get to dodge the traffic going to and from work

Something interesting you said there. The upstream O2 Sensor is the only sensor I have not replaced yet ... It looks very rusty and old and I doubt that it has ever been replaced. I think I will get it replaced as part of the troubleshooting step...

 

also make sure you don't have an exhaust leak around the flex pipe (usually you can hear it or feel the air at idle) - that can throw off the front 02 sensor as well.

 

 

You can have someone else start the car, and use a tissue or smoke to look for any signs of air leaving the exhaust system. Yes, even a small leak could result in the loss of a few MPG, so it bears looking into. OTOH, sometimes there are other odd noises when our cars wake up in the morning. Kind of like me...