What to do about poor fuel econ in older car?

"NoneOfYourBiz" (goawaynowkthxbye) 03/28/2015 at 21:52 • Filed to: Hyundai, Elantra, fuel economy, MPG, L/100km, mileage, fuel injectors, fuelly

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Howdy fellow Opponauts.

My used car gets pretty poor fuel economy and I’m soliciting collective Oppo-wisdom for suggestions on improving this.

It’s a 2006 Hyundai Elantra GT (the XD2 variant - 2.0L Beta II engine, CVVT) with a bit under 100,000 miles on the odometer. I’m at least the second owner so I don’t have a history on it.

First: it’s not “the loose nut behind the wheel.” I drive like my grandmother - smooth, slow acceleration, thinking a mile ahead to avoid having to use brakes as much as possible.
Yes, it’s an automatic and I’ve been doing a fair chunk of city driving.

Drivers on Fuelly report a median near 30mpg; I’m averaging 22mpg. (I don’t rely on the trip computer’s mileage readout; I log my fill-ups.)

I’ve had the plugs and ignition wires replaced.

I’ve had the heater-core and coolant flushed, thermostat replaced.

downstream (rear) O2 sensor has been replaced.

Smooth most of the time, occasional rough idle but no stalling.

Ideas?

Valve clearance (lash?) is mentioned in the maintenance schedule but the local dealers don’t really seem to know much about that.

Things I’m thinking about:

Have fuel injectors ultrasonically cleaned. (dealership suggested this as a next step but they don’t have the facilities to do it)

Fuel filter?

Air filter? (doesn’t seem dirty)

Transmission flush?

More precise wheel alignment? (tires are correctly inflated)

Possible partial brake seizure/rubbing?

Bad wheel bearing?

CV joint worn?

Wait for warmer weather?

“Suck it up it isn’t a hybrid?”

Photos for either enjoyment or pity:

Stock photo but it’s nearly this clean:

NoIDontDriftmy240 > NoneOfYourBiz 03/28/2015 at 22:48

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Try to sort out the rough idle issue. Download a Factory Service Manual for your car (related car forums should have them) and look for valve lash specs. D.i.y or bribe someone who know what they're doing to adjust them back to factory spec.

Yes on all filters (they are cheap replacements).

Check Throttle plate/body for any carbon build up.

Opposite Locksmith > NoneOfYourBiz 03/28/2015 at 22:49

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I hate to say it but that sounds like a realistic real-world average

NoneOfYourBiz > Opposite Locksmith 03/28/2015 at 22:51

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Naw, that's OK!

I'm looking for this kind of feedback. :)

NoneOfYourBiz > NoIDontDriftmy240 03/28/2015 at 22:53

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Nice. Thanks for that.

I wish the factory manuals were downloadable; they used to be but no longer. (anyone? Bueller?)

I may just call around to dealers until I find one with a master tech who know value adjustment.

NoneOfYourBiz > NoIDontDriftmy240 03/28/2015 at 22:55

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Duplicate...whoops.

Opposite Locksmith > NoneOfYourBiz 03/28/2015 at 23:07

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I had a similar age accent as a rental for a month and received similar efficiency estimations. Stay cool, friend

AMGtech - now with more recalls! > NoneOfYourBiz 03/28/2015 at 23:17

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I would try an indy shop if you haven't found a dealer who has a clue. Unfortunately for you Hyundai is not really a brand that most talented techs want to work for, so you might have a hard time finding someone in a dealer who knows what to do. But someone at an indy who knows Asian cars shouldn't have an issue.

For fixes you might be looking at filters, valve lash, fuel injection/induction cleaning service (I like BG brand, it is NOT a snake oil), check for torn vacuum hoses and fault codes. Make sure the car is up to date on maintenance and generally in good working order, then tackle the rough idle. Find someone who likes tackling tricky driveability issues, a lot of guys don't or can't.

But if all you do is city driving then your mileage might be perfectly normal.

Destructive Tester > NoneOfYourBiz 03/28/2015 at 23:17

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On your "Wait for warmer weather" question, are you in an area with winter blend fuel? That alone is typically good for a 2-3 mpg loss. Keep paying attention till May-ish when the changeover usually happens and you'll most likely find your combined mpg jump to the mid-20's.

NoneOfYourBiz > Destructive Tester 03/28/2015 at 23:36

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Yup, I'm in a part of the world where we definitely get winter formulation gas. I'll certainly pay attention as summer rolls around to see if it affects fuel economy. Thanks!

Delusion77 > NoneOfYourBiz 03/28/2015 at 23:37

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if it were your brakes rubbing or a poor alignment you would notice it while driving, but you can have a look at your tread wear and check if the pads are unevenly worn or your rotors are all gunked up.
Do you have winter tyres? In the summer when you swap to summers or 'all-seasons' you may notice an improvement especially if you have low rolling resistance tyres.

NoneOfYourBiz > AMGtech - now with more recalls! 03/28/2015 at 23:39

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*nods*

The car isn't throwing any codes and all the dealer came up with was the reading off the O2 sensor was at the "edge of tolerance." Perhaps though it wasn't a faulty sensor but something upstream causing the car to run rich.

I'll consider running a can of BK44 in my next tank of gas before committing to having the injectors cleaned and we have a few good indy shops around town that know Asian cars. Time to talk to them!

AMGtech - now with more recalls! > NoneOfYourBiz 03/28/2015 at 23:43

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The stuff that goes through the tank may not be enough at this point. They have stuff that you run through the intake and directly through the fuel rail with the car's fuel pump shut off, so the engine runs solely on the cleaner. That stuff works wonders on carbon build up.

Destructive Tester > NoneOfYourBiz 03/28/2015 at 23:52

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It's not a perfect comparison, but my bike usually only gets 45-50mpg on winter blend and 55+ on summer. Granted, it has a basic TBI with no real-time engine mapping but those are consistent real world numbers I've kept track of because it's the difference between a fun ride and an 8-10 mile walk of shame in race boots...

Zipppy, Mazdurp builder, Probeski owner and former ricerboy > NoneOfYourBiz 03/29/2015 at 00:20

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If the car is running rich, it there could be a vacuum leak in one of the pipes somewhere as well, a smoke test wouldn't hurt. Scotty Kilmer shows how to make a smoke device.

NoneOfYourBiz > Delusion77 03/29/2015 at 09:24

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Yes, running winter tyres so that's probably a small hit.

Alignment isn't way off - no pulling left or right - but perhaps it's off enough (toe in?) to add a bit of drag.

Brakes would have to be a very slight rub so I'm not too worried there; I can't hear any rubbing so it would be the tiniest of contact.

I'll mention both to my mechanic and check the tyre wear when I swap them in a few weeks. :)

NoneOfYourBiz > AMGtech - now with more recalls! 03/29/2015 at 09:31

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Interesting.

That was what my dealer wanted to do - injector and rail cleaning. I wasn't convinced it was as good as ultrasonic injector cleaning but you're saying it does a good job. I'm torn now between that and ultrasonic. They're both likely going to be several hundred.

AMGtech - now with more recalls! > NoneOfYourBiz 03/29/2015 at 10:33

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Not all fuel system cleaners are created equally. BG is generally considered to be one of the best, and they're approved by multiple manufacturers. I don't personally have any experience with too many others, but I do know that they don't all work equally well. Ultrasonic cleaning requires removing the rail and injectors and then sending them out to someone with the proper cleaning and testing equipment. That method will be significantly more expensive due to the labor involved. Whereas the other method does a great job for probably well under $200, without removing any parts.

NoneOfYourBiz > AMGtech - now with more recalls! 03/29/2015 at 11:07

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*nods*

There's an actual shop about an hour and a half from me that specializes in ultrasonic injector cleaning. If I go that route, I'd schedule a day trip and have them do it while I wait.

This is they: http://fuelinjectorprecision.com/order.html

I'm wondering if I should just spring to have the rail and injectors flushed at the dealer before doing the ultrasonic, on the grounds that if there is something gumming up the rail, there's no point in cleaning the injectors first as they could get clogged again after a rail cleaning.

AMGtech - now with more recalls! > NoneOfYourBiz 03/29/2015 at 13:26

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Their service is $30x4, plus labor to R&R, probably totaling $4-500. And it would do an amazing job of cleaning the injectors only.

Or you can spend $1-200 to do a pretty good job of cleaning the rail, injectors, valves, and combustion chamber. I've used this lots of times to take care of issues just like yours, and have looked at the inside off the engine before and after to see the difference made. It isn't perfectly clean, but it does do a very good job and takes care of any large build-up areas that would cause the most problems.

I'm not saying don't use their ultrasonic service. They do an amazing job and can all but bring a dead injector back to life. I've had this done many times as well, but it isn't often necessary. Also, consider the cost of new injectors against the service of cleaning. They're already being removed from the car to be cleaned, so it would be just add easy to install new ones. I've seen injectors as low as about $20 depending on application.

NoneOfYourBiz > AMGtech - now with more recalls! 03/29/2015 at 20:44

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Nice. Thanks again for the detailed response. You've given me a lot more confidence that the dealership fuel rail and injector flush has potential to help.