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very bad gas mileage

 
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Old Oct 31, 2009
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Exclamation very bad gas mileage

i have a 92 civic hatch with a d16y8 that gets about 12 mpg. i've put in a new o2 sensor and map sensor. what else can i do? i can't drive fast because i have to put in my new clutch. but my oil turns black after a couple weeks. i do have an exhaust leak in my headers. but it's not that bad. the exhaust does come out black though.
Old Oct 31, 2009
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Re: very bad gas mileage

sounds like you are running too rich (too much fuel, too little air). im not sure where to start, maybe check the usual maintenance items like plugs, air filter, intake system parts (make sure they are cleaned up), injectors may not be spraying properly. try the gas and oil additives in my sig below
Old Nov 1, 2009
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Re: very bad gas mileage

ok, well i started with taking apart the air filter because it's an aftermarket. and i saw that a sensor wasn't plugged in. i found out that it's my tps but when i plugged it in my car revved kinda high, then leveled a little but it was still high. then the car just shut off
Old Nov 1, 2009
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Re: very bad gas mileage

you need to reset the ecu after plugging everything back in. warm up the engine, turn off, then disconnect the battery. reconnect, start car, and let it idle 15 mins without any accessories or pressing gas. then turn off. you may want to clean the intake system parts and idle valves before doing the idle learn as well, and make sure the TB and other gaskets are sealing properly.
Old Nov 2, 2009
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Re: very bad gas mileage

i don't have any way of telling if my gaskets are sealing properly. but i reset the ecu, and tried to let my car warm up but it kept shutting off. so i drove it around until it warmed up, which was pretty difficult. then i parked it, disconnected the battery and reconnected it. started the car and it idled at a couple different rpms and then just died. i tried it at least three times. so i just disconnected the tps.
Old Nov 2, 2009
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Re: very bad gas mileage

may be a bad tps sensor then. its reading the wrong throttle position and the ecu is getting confused. and usually its easier to change the whole throttle body. they are around $50 on ebay for a used one.
Old Nov 2, 2009
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Re: very bad gas mileage

i just took my car to the honda dealership. they looked at it, told me i had the wrong intake manifold on it and that i needed a fast idle thermo valve and gasket...they wanted to do it for 400 dollars.
Old Nov 3, 2009
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Re: very bad gas mileage

Originally Posted by hatchkid92
i just took my car to the honda dealership. they looked at it, told me i had the wrong intake manifold on it and that i needed a fast idle thermo valve and gasket...they wanted to do it for 400 dollars.
I call BS on their behalf. $400! Damn what a rip off! Post pics, I'm almost certain your intake manifold is fine. Since you have a d16y8 engine, did you also get a d16y8 ecu? That would be my first guess and if the answer to that is no, get a new ECU. That'll be why you are running rich. My second guess would be either one or a combination of these; bad/dirty injectors, clogged fuel filter, bad spark plugs, bad spark plug wires, &/or a bad distributor cap and rotor.

To be cheap, if you do have the correct ECU, check and replace, if needed, your fuel filter. Then run a fuel injection cleaner like Gearbox recommended. I don't know when you last replaced your spark plugs but if its been awhile then just replace them and while you're doing that check the wires for any cracks.
Old Nov 3, 2009
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Re: very bad gas mileage

haha usually you can take off and clean the idle air and fast idle valves for free with carb cleaner and they will be just fine.
Old Nov 5, 2009
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Re: very bad gas mileage

do you know where i can get a fast idle at? honda wants like 120 bucks for one
Old Nov 5, 2009
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Re: very bad gas mileage

and i'll put up some pics sometime this week hopefully
i have to find my camera
Old Nov 5, 2009
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Re: very bad gas mileage

just clean the one you have. they rarely go bad. or check ebay
Old Nov 6, 2009
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Re: very bad gas mileage

alright, i'll give it a try
Old Nov 7, 2009
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Re: very bad gas mileage

so, i found my camera. so i have pics of my car now
 
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