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Thread: Causes of Bad Fuel Economy.

  1. #1
    Junior Member Carport Converter Z2TT's Avatar
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    Default Causes of Bad Fuel Economy.

    Hi,

    I've owned 2 GZ20's, and on my current one I'm noticing it's using a lot of petrol, About 25l/100km. I've checked things like filter, all clean and not sucking any hot air in, plugs/leads and distributor are good. Could the fuel filter affect fuel economy? I wouldn't think so but just a wild guess.

    Its so bad I even think I have a leak in the tank, so I checked under the car but no smell of petrol.

    What are possible causes of bad fuel economy, open to all suggestions.

    Thankyou.

  2. #2
    Toymods Club Member Conversion King big_zop's Avatar
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    Default Re: Causes of Bad Fuel Economy.

    Most of this should be able to be found with a simple search - netting you either a factory manual (which othen have a troubleshooting section, with patricular attention to poor gas mileage) or something else of use.

    While you may not find any information that is 1G-GTE or GZ20 specific, Toyotas of that era tended to operate quite similar so most information found could be useful to your application.

    Although, usually you will find that it will come down the ECU and operating parameters so it can be electrical or mechanical or a combination of the two and you will need to check that they are operating correctly, not just that things are clean (although that is a start). These arent in any particular order and you may only be able to check certain things but at least its a start:
    - EFI and electricals: start with the O2 sensor, stuck injector, cold start injector, crank sensor, spark plugs, engine timing
    - sensors that affect fuel delivery - temp sensors, afm, thermostat (yes, i had an issue with this on my car)

    Also, check the operation of the auto/manual (clutch slipping?) and if the brakes a dragging, as they can aslo affect it as well. How are you driving the car, has anything else changed with your driving habits, moved house and now spending more time in city traffic (although i do admit that 25L/100km is quite horrendous).

    In order for others to help you, you need to help yourself. Always remember to search first and then ask questions later.

  3. #3
    Junior Member Carport Converter Z2TT's Avatar
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    Default Re: Causes of Bad Fuel Economy.

    I did do a search before posting, couldn't find much information on fuel economy.

    Since I cant find a manual for the 1g-gte, would it be safe to use the 7m-gte manual, thing is I'm not sure if all the sensors are the same, because for things such as AFM and Cold start injector, the TSRM has resistance values listed, which I should check using a multimeter.

    How could the cold start valve cause excessive fuel consumption, only way I'd think is if it would be staying on all the time, and wouldn't the operation of it be affected by the coolant temperature?

    The coolant temp sensors I assume are fine, because as the car warms up the temp display on the dash reads upto half way.
    Also checked for air leaks, none. Checked Ignition Timing, it's at 10 deg BTDC. No engine Error codes.
    Auto doesn't act like it's slipping, shifts well, doesn't drop gears.

    Brakes I checked, all good.
    Last edited by Z2TT; 02-08-2009 at 09:18 PM.

  4. #4
    Forum Member Grease Monkey
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    Default Re: Causes of Bad Fuel Economy.

    Does your rear bumper have alot of burnt ash build up or on the exhaust? If so that is defenatly a fuel prob. With my R31 i had, the FPR was split which cause it to flood fuel into the intake and get me 70 kms from ten liters of fuel instead of 120km so i reackon its worth checking.

  5. #5
    Toymods Net Nazi Too Much Toyota river's Avatar
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    Default Re: Causes of Bad Fuel Economy.

    Hi,

    Even if the coolant sensor is showing the proper temp, that does not necessarily mean the signal is getting to, or being acted upon, by the ECU.

    At cold start you have a rich mixture. If this is engaged all the time, either by something jammed/broken or the ECU is playing up, you will be consuming more fuel. Check your plugs and see if they have thick soot-like grime over them, which shows the mixture is rich.

    seeyuzz
    river
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  6. #6
    Toymods Club Member Conversion King big_zop's Avatar
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    Default Re: Causes of Bad Fuel Economy.

    Most sensors will be similar but i cannot say for certain if they are.

    Youre problem is that you are assuming too much is working correctly. The dash gauge, engine temp and CSI all run a different sensor and assuming one is correct will not guarantee the others are. The injectors could have got a piece of dirt in them and can get are stuck open. The thing is you dont know for certain and need to eliminate as much as possible options before you start with big things like pulling out injectors, buying expensive components, sending to a mechanic, etc.

    My car started having higher fuel consuption when the only thing changed was my dad opened up the radiator cap and filled it with water - turns out i had a dud thermostat and my engine ran cold so was rulectant to change into OD and obviously got more fuel than was necessary because the ECU thought it was colder than it actuall was.

    And if you cant find a manual then you arent looking hard enough (granted the only one i have ever been able to find is in Japanese, at least numbers the numbers are there to read).

  7. #7
    Junior Member Carport Converter Z2TT's Avatar
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    Default Re: Causes of Bad Fuel Economy.

    el corona rear bumper has no ash buildup or black residue.

    River I'm not absolutely sure whether the car runs rich all the time, when cold the fuel smell is definately noticable, when it warms up cant smell it. I checked the plugs a week ago, they did not have any black soot on them, looked good.

    big zop I checked I have 2 coolant sensors near the thermostat, I'm pretty sure that is all, the other 1g i took apart didn't have any other coolant temp sensors apart from those 2. As for leaky/stuck injectors, wouldn't I get a puff of black smoke when starting the car after it's been sitting a while? or not necessarily

    I'd like to ask because I am losing this much fuel, and if the problem were a leaking fuel tank, would I notice it, as in would I be able to smell the fuel?

    Thanks.

  8. #8
    Fuel Economy Warrior Carport Converter Vios-GT_07's Avatar
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    Default Re: Causes of Bad Fuel Economy.

    hm..

    servicable items wouldn't make that much difference.. i agree that your problem here is mechanical or electrical.. air filter, spark plugs, fuel filter etc only affect fuel economy by so much.. at most there'd be a 2 to 3 liter per 100 km difference..

    are you running standard boost? do you drive like grandma all the time?
    Research has shown child in front seat causes accidents, accident in back seat causes child

  9. #9
    Forking Architect Grease Monkey
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    Default Re: Causes of Bad Fuel Economy.

    Quote Originally Posted by Vios-GT_07 View Post
    hm..

    are you running standard boost? do you drive like grandma all the time?
    who does

    ...but thats pretty atrocious!

    have you changed your exhaust sensor? Ive noticed a few peoiple on here running into trouble with them thats all.

    my second guess is fuel line itself....either leaking petrol under the car or close to the block....it will be 20-25 years old now and beginning to perish.

    meybe try running a current to your fuel pump (you cant turn yours on without turning the actual engine on can you?....I think weve had this conversation before)...and then go leak hunting with the car off the ground....if your losing an extra 10-15L/100km it hould be pretty profound

    hope this helps!!

    me
    Rotaries are cool...so why are their owners such cocks>>?

  10. #10
    Junior Member Carport Converter Z2TT's Avatar
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    Default Re: Causes of Bad Fuel Economy.

    Hi,

    I'm starting to think it could be the o2 sensor itself, But I really cant find a definitive way of testing it. I remember reading up a while ago about taking it out, heating it up with a blowtorch then measuring with a multimeter and see if the voltage fluctuates. Could I test it in car while the car is idling?

    As for the fuel tank or line leak, I'm going to have a look. I definitely cant smell any fuel in the car when driving but I will still have a look as I'd think even the smallest hole would leak a lot of fuel to be noticable. Actually I can turn on the fuel pump with the car off. Lexmaz from here told me how to do it, when the car is on ignition just push the airflow meter flap in and the fuel pump will turn on. Is there any sort of "sniffer" type device that can help with the detection of fuel leaks?

    Other than that the only thing I can think of is taking the petrol tank out and getting it pressure tested.

  11. #11
    The old One Backyard Mechanic
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    Default Re: Causes of Bad Fuel Economy.

    Gidday

    Are you really getting 25l/100 or is that an off the head figure. I would expect to get 10-13l/100 or better in normal circumstances.

    Lets put it in perspective 25l/100 is what I would expect to get out of my bigblock Ford Thunderbird on a bad day..

    Clarification would help diagnosing the problem.

    Craig

  12. #12
    Junior Member Carport Converter Z2TT's Avatar
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    Default Re: Causes of Bad Fuel Economy.

    Yes I am really getting about that much.

    Last Monday I refilled with $50, giving me about 40L. This bumped the fuel meter to 1/2 way. I travelled about 80km from then until Thursday and the fuel meter was at 1/4 way, so i had lost about 20 Liters. If I were to travel say 100km not 80 That would have probably been 25L. That is how I got that figure.

    I will try turn the fuel pump on and have a look around for leaks from the fuel tank to the engine, other than that any other suggestions would be good. Ussually I would be getting 12/100 which is what I got on my previous car which was the same model.

    Thanks.

  13. #13
    AGE-16V Automotive Encyclopaedia Dimmy's Avatar
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    Default Re: Causes of Bad Fuel Economy.

    Is this something that has happened recently or since you've had the car?

    My car has started drinking petrol like it's going out of fashion and is getting about ~350/45L in a 4age, it used to be 400-450/45L I noticed it started happening after the huge downpours we had we I drove through a large puddle and got water from oncoming traffic which entered the engine bay and flooded the spark plugs.

    I'm yet to get some degreaser on them to see if it fixes it, but I think it would be a big coincidence if something else is causing the issue...at least in my case.
    I have been pruned by old man river!!!!!

  14. #14
    Forking Architect Grease Monkey
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    Default Re: Causes of Bad Fuel Economy.

    ....I cant remember...is there a clip to take your 02 sensor off your loom in a reasonable place (ie, in the engine bay)??

    If so there might pe someone up your neck of the woods who could swap for a direct comparison test\

    Im not sure though....if your not smoking (more than usual) and you dont have black deposit around your exhaust....then it has to be going somewhere!!
    Rotaries are cool...so why are their owners such cocks>>?

  15. #15
    Junior Member Carport Converter Z2TT's Avatar
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    Default Re: Causes of Bad Fuel Economy.

    Hi,

    Dimmy it's been like this since i've had the car.
    LT1986 yes there is a plug to unplug the o2 sensor in the engine bay.

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