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I think my car is consuming much more fuel than it should, I've compared it to other versions of the same model which have more powerful engines and mine seems to be on the higher end when is supposed to have the most economic engine of all. I have a Toyota Altezza (which is exactly the same as the Lexus IS200), it comes with a 1G-FE engine, which should be more economic than the 3S-GE and the 2JZ engines.

Things I've done so far:

  1. Cleaned the air filter (the air filter is a cleanable one, not just dedusting a replaceable filter)
  2. Replaced the spark plugs (got the original Iridium replacement part)
  3. I have the original wheels and use the tires sizing and air-pressure specified by the manufacturer 215/45/17 @ 34 pounds (2.3).
  4. All my engine indicators on the dashboard are off and the BSOD check showed no error code (they all turn on when I engage the switch).
  5. I don't (usually) drive at high-accelerations/high-speeds.

I'd like to know what else can I check on my engine that might lead to a poor fuel efficiency.

Note: some time ago I had my engine serviced and they left the air sensor that goes after the intake filter unplugged and this didn't turn the check-engine indicator on, I didn't give it a BSOD check during the time the sensor was disconnected though.

Update 1

I'm getting around 22 MPG when I should be getting around 35... the 2JZ which is the most fuel-hungry version has 20-25 (in cars with similar mileage), I got the car like 6 months ago and is always been like that, the previous owner and the mechanics I took it to said the engine hasn't been mod (and knowing a bit on the subject as well, I think so too). The Altezza is produced for the Japanese Market (with high standards though) so all the average consumption I've inferred on how much all the other stock cars in my team consume.

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On what are you basing your estimates of what the car should consume? Was it getting better mileage and then something changed? Or are you comparing to marketing numbers? There are plenty of external factors that can affect mileage: for example, even if I drive slowly and carefully, my commute involves two fairly steep bridges. There's a cap on how good my mileage is going to be. –  Bob Cross Oct 22 '13 at 13:48
    
I think the consumption is high because I compared it to other cars in my team that have different (stock) engines, similar use and consume less. –  PedroC88 Oct 22 '13 at 14:50
1  
This comparison would be more useful to you if you were comparing identical cars with indentical engines, usage and driver. Has this vehicle ever demonstrated the fuel consumption numbers you were hoping for? If not, were you deceived by marketing numbers? If so, did something change? –  Bob Cross Oct 25 '13 at 12:25

5 Answers 5

I think you are right on track. Taking a look a Fuelly there are 5 other Altezza owners and they all seem to be getting about the same MPG as you do: http://www.fuelly.com/car/toyota/altezza

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That is a nice site, and yes, those Altezzas mentioned there have the same engine I have, so perhaps the consumption of the engine increases a lot over time, much more than intended by the manufacturer. –  PedroC88 Oct 22 '13 at 13:20

How much worse is the fuel usage you are experiencing? Have you talked to any other owners to see if you are getting way below their mileage? How did your last car perform compared to listed fuel mileage ratings?

In the U.S., the government posts the results of required fuel mileage tests. Most of the people I have talked to do not get the same fuel mileage as the test cars do. Some say the city mileage is worse than expected, and some say the highway mileage is better. Of course, this is anecdotal evidence, because no one drives the exact same way everyday. In addition, the government tests are performed under laboratory conditions, while for individuals there are many other variables, such as: the weight of the car (1/4 of a tank of fuel vs. a full tank), traffic, how long you idled at a red light, how many hills you climb, etc. The best you can get is a long term average.

In my area we use an ethanol blended gasoline. On a recent trip I noticed a 10% increase in mileage when the fuel I purchased was not an ethanol blend. While all the things that you have checked will have an effect on fuel usage, the biggest influence is the driver.

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Updated answer, also, about my driving tendencies, I usually drive home-work which is 6-9 miles both ways, depending on the route, with not many stop lights. –  PedroC88 Oct 21 '13 at 23:55
    
After doing some searching at various Altezza forums it seems that many owners get lower fuel economy than they expected. –  mikes Oct 22 '13 at 10:36

I'm not really familiar with your car, specifically, but I'm ready to speculate based on general knowledge of fuel injection.

Electronic Fuel Injection or EFI uses 'closed loop air/fuel ratio control'. What this means is that it has a way to 'see' how completely the oxygen has been used up by the fuel delivered. If there's too much fuel, there will be no oxygen left. The car's computer then reduces the amount of fuel used until it sees too much oxygen in the exhaust, and increases fuel again.

The sensor used to do this is the oxygen sensor, or O2 sensor. Though the check engine light should come on if this sensor isn't giving good enough feedback, it might be worth measuring its output. The best way to do this is with a graphing voltmeter which can show a plot of the sensor's voltage.

Once the car is warmed up the o2 sensor voltage should oscillate maybe 30-60x per second, passing through 0.5v. If you just have a multimeter with a digital display, you would look to see around 0.5v constant DC. Steady 1v or 0v indicates a problem either with the sensor or with fuel delivery... but it's a place to start. The sensor will have a few wires on it, and the relevant signal is usually on the black one. YMMV, it might be worth looking at a wiring diagram to be sure.

It's interesting that leaving the airflow sensor disconnected did not trigger a check engine light, too. That sensor is also responsible for giving the computer a baseline fuel quantity before it's adjusted by oxygen sensor feedback. Almost every car I've ever touched will throw a code and illuminate the check engine light if this sensor is disconnected.

I wonder if the car's ECU has been modified by a previous owner. Is this a possibility? Has someone 'chip tuned' it and F'd it up? Chip tuners frequently attempt to change the fuel table referenced by the airflow sensor's input.

Lastly, I have found that re-usable air filters typically require that they are oiled lightly to catch small particles of dust. If any of this oil ends up on the element of the airflow sensor it can make it report the air mass incorrectly, which can affect fuel consumption. There are cleaners available for the MAF, you could try that out.

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I did find the fact that the check engine light didn't turn on when the sensor was disconnected odd, and the chip has been modded indeed, 'cuz these engines come with a 180 Km/h ECU limitation, and I could take mine up to 200 Km/h (engine's max). I already swapped and sold that engine, but your answer was really helpful :). –  PedroC88 Feb 8 at 14:27
up vote 1 down vote accepted

Apparently there's one more thing you can check to see if you're engine is consuming too much, and that is the composition of the exhaust gas. I took my engine to a dyno before swapping it for a 2JZ ('cuz hey, if I'm gonna the 2JZ mileage anyways, might as well get power) and they told me the engine was getting more fuel than it should.

Apparently the engine fuel intake regulator wasn't regulating properly but still "working" so no engine issue was detected.

I would still recommend to go through the steps in the original question, and if that all fails then take it to the dyno and measure the air/fuel ratio through the exhaust gasses.

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Good day I am from Trinidad and own an Altezza with a 1G- FE engine. I couldn't help but notice you mentioned that you washed your air filter. I previously used a K&N air filter in it and purchased a regular replaceable Sakura air filter for it . The Sakura was supposed to be used for periods when the K & N needed to be cleaned since proper drying is necessary for proper and safe function of the k & n . Anyway, when I did start this practice of using the sakura, I realised a significant increase in fuel economy. Personally, without any research being done, I believe this is as a result of the k&n filter having a thinner filter media which allows more air into the intake manifold which causes the brain to increase the amount of fuel it sends to the engine to compensate for the increase in air. This is my personal experience and may be subject to correction but it happened with me . I hope it may have helped.

Regards

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