Aveo Gas Mileage - Good then not so Good

I recently read a post on ways of improving fuel mileage on Chev Aveo's. As per the post, I replaced my air cleaner (which was a fairly new OE GM air cleaner) with a K&N filter and a set of new spark plugs. The old stock air cleaner looked okay, but the spark plugs were BADLY eroded (about 70k on it at the time). Mileage jumped from about 350km per tank (mostly highway miles) to over 500km per tank (sometimes over 550km).

My mileage is starting to drop again to around 400 to 450km per tank. I cleaned the K&N air cleaner (as per instructions and replaced filter oil) and checked the plugs. Some slight erosion, but still in spec (0.044 inch gap).

My only thoughts are that mileage would be dropping (now down about 20%) due to the change in temperature - I did the tune up in summer when the temp was about 25C and now its about 5C.

Any ideas....?

Anyone....?

Winter mileage will always be lower. Your mileage should be increasing now that its getting warmer out. Wait it out a few more tanks and keep track of your mileage to be sure.

I agree that winter has an affect on fuel economy and I do see my fuel economy rising now that the temps are above freezing. Problem is, I did the tune up (K&N air filter and plugs) last May and watched the economy go down in late summer/early fall - well before winter. Then it went down slightly more in the winter.

I have noticed that when I do an ECU re-learn (aka, pull the battery cables), my fuel mileage goes back up, but then back down again after one tank. No CEL has come up, but I haven't check for error codes. I'm wondering if it isn't the O2 sensors, but I haven't got around to checking them.

If it's good after disconnecting the battery it might do worse as it learns your driving style? How do you typically drive? The car could be running lean during the learning curve giving you the extra mileage.

Converting that though you sound really low with typical driving is that Mostly city?

Most of my driving is commuting back and forth to work on the highway at about 100-110 km/hr. Some limited city driving. As I said, with the same commute, same driving style and just the replacement of a filter and plgs (I didn't remove the battery cables for that, so no ECU reset), I jumped from high 300's to mid 500 km per fill up (I do calculate by odometer and litres per fill so that I do calculate this more precisely). After a few months, mileage started to go down again.

I've tried varying my driving style, changing where I fuel up, and two treatment of GM fuel injection cleaner. Noting has significantly changed my fuel ecomony.

You need to actually log your mileage if you want to analyze things. KM per tank is just about the least accurate way to measure things. Your gas gauge is pretty inaccurate. Its basically there just to tell you when the tank is getting low. I suggest logging your miles driven and gas used at each fill up and calculate the mileage manually. Its the only way to know for sure what the mileage is. From that you can see what you are getting versus what you are supposed to be getting per the EPA and go from there.

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Originally Posted by Daox

You need to actually log your mileage if you want to analyze things. KM per tank is just about the least accurate way to measure things. Your gas gauge is pretty inaccurate. Its basically there just to tell you when the tank is getting low. I suggest logging your miles driven and gas used at each fill up and calculate the mileage manually. Its the only way to know for sure what the mileage is. From that you can see what you are getting versus what you are supposed to be getting per the EPA and go from there.

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Thats precisley what I do:

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(I do calculate by odometer and litres per fill so that I do calculate this more precisely

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What I should have said is "trip odometer". I don't have my Mileage Excel spreadsheet on this computer, but I have tracked fuel consumption per km/mile since I bought the car, based on the method you suggested. It has definately varied substantially. I'll look at the numbers tonight and post some examples.

Woops missed that. :oops:

Yeah, post the numbers up and we'll figure stuff out.

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Originally Posted by Daox

Woops missed that. :oops:

Yeah, post the numbers up and we'll figure stuff out.

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Not a problem. Okay, here are some numbers. These will be in a litres/100km, Miles/US Gallon and, Miles/Imp Gallon. All numbers reported are primarily highway miles.

The BEST mileage I ever had in this car, was shortly after I bought it in 2006, which was 6.73/34.94/41.97
The worst ever highway mileage was 9.81/23.97/28.78 in January 2010. The mean temperature was around -19C

RIGHT before I did the K&N filter/spark plug tune up in spring of 2009 it was 9.61/24.46/29.38

RIGHT after I did the K&N filter/spark plug tune up in spring of 2009 it was 7.97/29.50/35.43

It was up to 7.44/31.61/37.7 at one point.

By October/November 2009, I was averaging 9 litres/100km (26 miles/us gallon).

Just to show this isn't seasonal, I was routinely getting 7.8 litres/100km average (30.2 miles/US gallon) in January of 2007!
The mean monthly temp that year was -16C

According to the EPA ratings (not sure if you're auto or manual or exactly what year it is), but your combined rating is only around 9l/100km (26 mpg US). So, you are beating the rating for the car. Also, according to the EPA's site, most users are getting around 8l/100km (29 mpg US).

That being said, there are many things you can do to increase your mileage. I see no reason why you can't be getting around 7l/100km (33 mpg US) with a bit of tweaking.

The posted EPA mileage of 26 mpg is for mixed city/highway driving, assuming about 50/50. My mileage estimates are for almost exclusively highway driving (about 90%). I do have mixed and city estimates and they are considerably below the values I have presented. Therefore, I should be getting closer to the EPA estimate of 31 mpg.

That being said, I'm not interested in comparing my car to the EPA of NRCAN estimates (according to NRCAN, I should be getting 6.4l/100km on the highway!). What is more meaningful is comparing my car to its mileage history. On average, my car is getting 20% worse fuel economy than it has in the past and this is irrespective of season and outside temperature.

Sooo....I'm looking to determine why and for any ideas/tips people may have. It was a tip I read on this forum that lead me to change the filter to a K&N and to check the plugs. I don't think the filter did much, but the spark plugs were definately shot (badly eroded). That made an immediate and substantial change of almost a 23% increase in fuel ecomony. What was weird, was that after about 5 months, the economy started to go down again.

Any ideas would be appreciated.... :scratch:

what kind of plugs did you put in? check them again?

you could check the o2, iat, and map sensor signals.. those could be off
but only the o2 would have potential to adjust back with a plug change, but going bad again that quickly? not sure about that..

How many miles were on the old plugs? were the 4 uniform in their condition? did you replace the wires or check the coil pack?

if you had that terrible of a ignition system before the change you could also have a clogged cat, or partially clogged. That would restrict your mileage, an with new plugs you would have been able to temporality burn out some of the cat to show improvement (no scientific data to back it up, but the heat from the properly burning cylinder transfers to the cat to allow it to function, a properly running engine with semi clogged cat would could get hot enough inside the cat to burn off some restriction). Theory, a fully clogged cat on some cars can bend valves, i replaced an engine or two because of that.

Thanks petrified.rabbit:

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what kind of plugs did you put in? check them again?

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I put in regular NGK V-Power - not iridium. My 2005 had stock regular AC Delco's, not the Delco Iridiums recommended in the owner's manual. The old plugs had badly worn central electrodes, but all wear was uniform. All had proper coloration (light tan to brown). I did check them again. I will have to check my notes as to when, but I would guess 5 to six months after install when mileage started to go south again. The new plugs had good electrodes, but all of the plugs had a black sooty color. I checked them again later (after the car had run awhile after a commute) and the color was better. I'll check them again tonight. I was definately thinking too rich of a fuel mixture when I saw those sooty plugs.

Note again that I have a K&N drop in filter that was installed April 2009 and cleaned in November 2009 (just before winter).

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you could check the o2, iat, and map sensor signals.. those could be off
but only the o2 would have potential to adjust back with a plug change, but going bad again that quickly? not sure about that..

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I haven't tested the O2 Sensors. I don't have a scanner and I haven't checked for codes. The CEL has never come on. That said, I plan on testing the O2 sensors using a multimeter using a onboard/in situ method.

I believe I have tested the IAT with a multimeter. I had a good "How To", but I didn't have a volts to temperature reference to use for a conclusive test. All I could measure was whether there was a "reaction" and the reaction rate in the IAT. I assumed the IAT is the only sensor on the air intake tube (after the air cleaner box).

I couldn't find a MAF sensor on the Aveo. If there is one, let me know where and how to test it.

Also note that my car has had the "cold weather intake" recall/upgrade done to it. This was to prevent potential icing of the throttle body.

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How many miles were on the old plugs? were the 4 uniform in their condition? did you replace the wires or check the coil pack?

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Assuming they were never changed, about 70,000 km (43,750 miles). The new ones have about 25,000 km. I did do a resistence check on the spark plug wires and they were consistent to each other. I'll have to see in my notes what the resistence was. I did not test the coil pack. How would I do that?

Would a compression test be they way to find bent/leaky valves? How would I test for a plugged CAT, other than smell? My understanding is that a bad CAT would smell like rotten eggs all of the time, no? Would the following be advisable?

"When a clogged converter is suspected, some mechanics temporarily remove the O2 sensor from the exhaust pipe ahead of the catalytic converter and look for a change in performance."

Thanks!

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Originally Posted by whitefish

Thanks petrified.rabbit:

I put in regular NGK V-Power - not iridium. My 2005 had stock regular AC Delco's, not the Delco Iridiums recommended in the owner's manual.

Note again that I have a K&N drop in filter that was installed April 2009 and cleaned in November 2009 (just before winter).

The CEL has never come on. That said, I plan on testing the O2 sensors using a multimeter using a onboard/in situ method.

I believe I have tested the IAT with a multimeter. I had a good "How To", but I didn't have a volts to temperature reference to use for a conclusive test. All I could measure was whether there was a "reaction" and the reaction rate in the IAT. I assumed the IAT is the only sensor on the air intake tube (after the air cleaner box).

I couldn't find a MAF sensor on the Aveo.

I did not test the coil pack. How would I do that?

Would a compression test be they way to find bent/leaky valves? How would I test for a plugged CAT, other than smell? My understanding is that a bad CAT would smell like rotten eggs all of the time, no? Would the following be advisable?

"When a clogged converter is suspected, some mechanics temporarily remove the O2 sensor from the exhaust pipe ahead of the catalytic converter and look for a change in performance."

Thanks!

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its tough replying to long posts on an iphone.. :lol:

1. i am not sure if the iridium plugs matter or not, i believe the later cars have regular ngk's in them? but i have the ecotec, not your engine so i have not personally verified that.

2. K&N drop in filter should not limit the system. but over oiling it can be restricitive, and REALLY over oiling it can foul plugs. But your talking winning the lottery odds there.

3. if there is no check engine light that means the problem might not be consistent enough to switch the light on. This is where knowing more about the daewoo computer would come in handy, typically its 2-3 occurrences in a row throws the light, then 3 without will shut it off. But the parameters of the signal might be within spec, but enough to cause fuel consumption problems.

4. The IAT sensor (i dont have this either) if it fluctuated it is probably ok if the range was acceptable, i believe typical failure results in an open circuit or high resistance.

5.You do not have a MAF but you have a MAP sensor, its kind of an indirect way of doing what the MAF does. it just reads vacuum instead of flow. Check that, and the vacuum lines for leaks.

6. I do a relatively old way of testing the coil pack and wires. start the car and mist them with water from a spray bottle. If there is a problem, you get a light show. just don't overly wet anything else and it is perfectly safe.

7. a compression test or cylinder leak down would be good for checking valve, most likely they are still ok though, running on 3 cylinders would be very noticeable.

8. that method to test for cat clogs works if the engine wont start at all from a totally clogged cat. it wont tell you too much since it runs, you would need to compare o2 sensor signals, or take of the cat and look through it.

Wow, responding on an iPhone! I'm impressed. =D> Thanks for all of the info (and sore fingers).

Where is the MAP and how would I test it?

WIth respect to testing the CAT, I saw a video on You Tube showing a procedure where you drill a small hole in the exhaust pipe in front and behind the CAT and test exhaust pressure in each hole using a pressure gauge. If the pressure is much greater in front of the CAT, then its plugged. Then you use a small metal plug to fill each hole.

That said, if a compression tester could thread into the O2 sensor hole then the same thing may be able to be accomplished using the compression tester and not drilling any holes.

I'm also going to see what my warranty covers with respect to the CAT. Maybe GM covers this!

90% of my online time is on my iphone, 10% is on a netbook.

Its hard running admin stuff on the iphone. so i switch to the netbook for that.

I am not sure where your map is, i would need to see under the hood (this is where i keep saying i have the ecotec). But follow the vacuum line diagram. it should be there.

threading a pressure difference reader into the o2 will work if you find the ends. but i am not sure you will find a compression test to work in the o2 sensor port, the way it works is a lot different. you almost need a "flow" meter.
or you would need to seal the end of the tailpipe and blow the rear muffler out the side. :lol:

there should be a 7-10year ish, 100000 mile ish. warranty on the cat. but what it is and such is hard to determine, plus going in without the check engine light would probably make them not replace it.

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Originally Posted by petrified.rabbit

90% of my online time is on my iphone, 10% is on a netbook.

Its hard running admin stuff on the iphone. so i switch to the netbook for that.

I am not sure where your map is, i would need to see under the hood (this is where i keep saying i have the ecotec). But follow the vacuum line diagram. it should be there.

threading a pressure difference reader into the o2 will work if you find the ends. but i am not sure you will find a compression test to work in the o2 sensor port, the way it works is a lot different. you almost need a "flow" meter.
or you would need to seal the end of the tailpipe and blow the rear muffler out the side. :lol:

there should be a 7-10year ish, 100000 mile ish. warranty on the cat. but what it is and such is hard to determine, plus going in without the check engine light would probably make them not replace it.

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I believe the service manual states that if the backpressure at idle is over 2psi to check for collased cat, pipes or mufflers. They do make gauges that screw into the oxygen sensor holes. They're just a metric thread.

Thanks guys! Where would I find this type of gauge? Can someone send me a link to one?

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90% of my online time is on my iphone, 10% is on a netbook.

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Have you tried out one of the iPad's yet?

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Thanks guys! Where would I find this type of gauge? Can someone send me a link to one?

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Whoops, nevermind. Found them. Yikes! Not cheap - at least not in Canada.

if its bigger than my iphone, it needs to be my netbook. i also have a desk top.

the ipad is like the "gitterbug" iphone. the iphone for extremely near sighted and old people who can hit little buttons..
:lol:

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Originally Posted by petrified.rabbit

if its bigger than my iphone, it needs to be my netbook. i also have a desk top.

the ipad is like the "gitterbug" iphone. the iphone for extremely near sighted and old people who can hit little buttons..
:lol:

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:laughing5: :laughing5: :laughing5:

Just checked my mileage on my last tank with about 80% highway and 20% city and it was 30.2 US miles/ga. This was after the computer reset/relearn. Lets see if this holds out on the next tank. Before this, I was averaging 27 US miles/gal

I'm getting aprox 30 US mpg, thats with 60/40 city highway, driving like a granny. will drop to 23-25 if i drive more aggressively or above 110km/h for too long.

I get 35 - 37 mpg (Imperial Gallon) running at 120kph with A/C running all the time. Drops to a lowest of 32 mpg at -40 in snow.