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Discussion Starter #1 (Edited)
bad gas mileage and I can't figure out why!***UPDATED***

ok so I've posted this a couple times and never got a definitive answer. the setup cx hatch with a d16z6 with about 100k I have changed the o2 sensor, plugs, wires, cap, rotor, set timing to factory specs, tested pcv, fixed exhaust leak, changed rims and tires. and I still get a consistent 23 mpg. what else could it be I have a cat on the way as soon as that gets here I'll replace my stock exhaust. As soon as Atmosfear puts his turbo on I'll put on the greddy header. I was going to either adjust my valves or have them adjusted. change my fuel filter. any ideas would be greatly appreciated. thanks:mikej:


edit* Ok today I changed the fuel filter and compression tested it the results were
#1-200
#2-205
#3-205
#4-210

lmk what you guys think.
and for the guy that wanted pics of the plugs

 

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Whats your compression and bad air filter has a lot to do with it. Im broke so im getting bad mileage lol
 

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Discussion Starter #3
it's a stock z6 so about 9.5:1 and it has an intake on it so it has a cone filter
 

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"Wild Bush Appeared!"
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Whats your compression and bad air filter has a lot to do with it. Im broke so im getting bad mileage lol
Could be my problem, I've dropped maybe 10 miles per tank and i've had my same filter since I bought my car. So, probably around 45k now :lol:.
 

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He means get a compression tester and check each cylinder compression. Also, keep oil changed in proper weight, same with tranny oil, keep tires inflated properly, new air filter if its dirty, drive easy.

Aside from that, pull your injectors and check to make sure they aren't cracked, and it also wouldn't hurt to run some Seafoam or lucas injector cleaner through it.

Also, where do you buy your gas? If you buy it somehwere like Murphy's at Wal Mart, they have gasohol, the 90% gas, 10% ethanol and i noticed a drop in my mpg by several mpg's when they made the swap, and thats running 93 octane. Also, if you hear any detonation, step up to a higher octane, although 87 should be fine for you.
 

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Discussion Starter #6
He means get a compression tester and check each cylinder compression. Also, keep oil changed in proper weight, same with tranny oil, keep tires inflated properly, new air filter if its dirty, drive easy.

Aside from that, pull your injectors and check to make sure they aren't cracked, and it also wouldn't hurt to run some Seafoam or lucas injector cleaner through it.

Also, where do you buy your gas? If you buy it somehwere like Murphy's at Wal Mart, they have gasohol, the 90% gas, 10% ethanol and i noticed a drop in my mpg by several mpg's when they made the swap, and thats running 93 octane. Also, if you hear any detonation, step up to a higher octane, although 87 should be fine for you.
yah I think I'll do a compression test this week and run some seafoam or something. as for gas a law passed in washington state where all gas stations have to run 10% ethanol. I seem to get the best mileage from costco gas.
 

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Does the vehicle have stock rim and tire sizes? when you swapped motor did you swap trans? If any of those have gotten changed from original standards then there is a possibility of gear ratio change. even the slightest change in tire size can change your gear ratio
 

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Does the vehicle have stock rim and tire sizes? when you swapped motor did you swap trans? If any of those have gotten changed from original standards then there is a possibility of gear ratio change. even the slightest change in tire size can change your gear ratio
good question/suggestion, new guy....
 

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Gasahol is stupid. We have 10% of the gas that is renewable, yet it decreases the gas mileage much more. It raises the octane level but ethanol doesn't create as much power for each gallon burned like gasoline (heat energy measured in BTU's). The Government thinks it's a viable option to ween us off of gasoline, honestly diesel is the way to go. I love diesels and the newer cleaner low sulphur diesel has just as much power potential as the older stuff, ask Gale Banks what he thinks of LSD (low sulphur diesel not the potent drug)
 

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Discussion Starter #10
Does the vehicle have stock rim and tire sizes? when you swapped motor did you swap trans? If any of those have gotten changed from original standards then there is a possibility of gear ratio change. even the slightest change in tire size can change your gear ratio
yes I just put stock 195/50/15 and gsr blades. it has an si tranny and everything. the only thing my car is missing to be an si is a sunroof, interior, and vins
 

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I would have to say that the transmission isnt helping your problem. the gear ratios are way different from stock to si. i meant to ask is that mpg on the street or highway?
 

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Discussion Starter #13
tire pressures good. its 23 mpg in the city. I know the tranny isn't helping but I just cant drive a dx tranny they suck.
 

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do the compression test, check the pulls for fowlness, clean the injectors...these things need to be done before we can give you any more "accurate" help...
 

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fuel filter is another good thing to change as well.this will kill your gas mileage and cause a low pressure hesitation, if it's bad enough.
 

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We get about 25 with our Y8 (all city). I've got a tune-up coming (fuel filter, plugs, wires, new air filter, etc.). Hopefully that'll help my situation.

Like Koots said, try the fuel filter. They're cheap and easy to replace, too.
 

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Be happy with 23mpg, with my foot i get liek 11mpg/ dx tranny

after i stopped taking the freeway, my mpg improved some :)
The Government thinks it's a viable option to ween us off of gasoline, honestly diesel is the way to go. I love diesels and the newer cleaner low sulphur diesel has just as much power potential as the older stuff, ask Gale Banks what he thinks of LSD (low sulphur diesel not the potent drug)
Im looking into a D- benz personally =b
 

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People think that a plugged fuel filter makes a huge difference, but in all honestly it doesn't. Thats my 2 cents after working on cars for over 6 years
 
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