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Gas milage

green_henry

Senior Member
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Pleasant Hill, CA
#3
^^^ +1, too vague.

If E30, then yes, definitely, you will see lower MPG, but 24 is pretty bad. As for top-end, what else do you have installed? FMIC? Upgraded radiator? Other? What you may be experiencing is heat soak rather than issues with the tune.
 


OP
G
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Location
Charlotte, NC, USA
Thread Starter #7
^^^ +1, too vague.

If E30, then yes, definitely, you will see lower MPG, but 24 is pretty bad. As for top-end, what else do you have installed? FMIC? Upgraded radiator? Other? What you may be experiencing is heat soak rather than issues with the tune.
Car is fbo. Intercooler and intake were on when I bought the car so they could be cheap. What’s heat soak?
 


Sam4

Member
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Location
West Chester, PA, USA
#10
I let the car calculate, almost never clear/reset, and I'm showing 29. I drive hard - hit triple digits a few times a week, but 70-85 normal highway. Are you a heavy mix of city driving? Doing the math or is the trip computer? How about sooty exhaust?
 


OP
G
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Location
Charlotte, NC, USA
Thread Starter #11
Car is fbo. Intercooler and intake were on when I bought the car so they could be cheap. What’s heat soak?
I let the car calculate, almost never clear/reset, and I'm showing 29. I drive hard - hit triple digits a few times a week, but 70-85 normal highway. Are you a heavy mix of city driving? Doing the math or is the trip computer? How about sooty exhaust?
I drive hard sometimes but I usually baby it. Nah no sooty exaust. Good amount of city driving
 


Intuit

2000 Post Club
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#12
Only trouble code is po141
Downstream Oxygen Sensor shouldn't affect operation or mileage; just there to monitor the catalytic converter. Adding to @Sam4's comment, how's AFR been reading? Another thing that kills mileage is unnecessary RPMs. Are the boost pressures unusually high? Any extra air, metered or not, have to be accounted for with extra fuel in order to maintain emissions. So if there's a problem with too much air, it's going to murder mileage.

Let's not skip the simple - tire pressures, alignment and brake drag
 


Intuit

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#15
I think last I calculated was like 28. But my larger diameter tire throws that off a bit. Other than the additional sidewall, my suspension and drivetrain (includes programming) are stock. It can't even come close, but do try to accelerate like the motorcycle (specifies 95 octane). So needless to say, crap mileage. 93 octane always in the tank.
 


OP
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Thread Starter #16
Downstream Oxygen Sensor shouldn't affect operation or mileage; just there to monitor the catalytic converter. Adding to @Sam4's comment, how's AFR been reading? Another thing that kills mileage is unnecessary RPMs. Are the boost pressures unusually high? Any extra air, metered or not, have to be accounted for with extra fuel in order to maintain emissions. So if there's a problem with too much air, it's going to murder mileage.

Let's not skip the simple - tire pressures, alignment and brake drag
AFR is right where it should b. I sent my datalogs to Jason at dizzy and he said everything looked good. Wheels are aligned. And tires have the proper pressure. Boost pressure is good, I’m tuned to 24 and it hits it when I step on it.
 


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WA, USA
#17
AFR is right where it should b. I sent my datalogs to Jason at dizzy and he said everything looked good. Wheels are aligned. And tires have the proper pressure. Boost pressure is good, I’m tuned to 24 and it hits it when I step on it.
wouldnt hurt to run a GDI injector cleaner through a tank of gas. but IME, ive never seen 24 mpg when i was fbo stock turbo on 92 and e30. city was 29, hwy was 34.
 


Intuit

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#19
AFR being consistently good, no relevant codes, is a great sign. Overcooling the engine (thermostat, radiator, bypass valve if present) can harm mileage and (very) slowly clog a catalytic converter.

Perhaps it's just a combination of a good intercooler and intake. Air control is major way in which manufacturers keep mileage in check.

Beyond that, general troubleshooting protocol dictates that everything be set back within expected/normal parameters. If all other hardware is stock, switching back to stock tune, then maybe intake, (intercooler not realistic) may be the next steps. Less likely but could check for vacuum and boost leaks; when small, I'm not sure that they always trigger codes?

I believe someone else wanted to verify how mileage is determined.
 


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Metro Detroit
#20
My car has the Mountune hoses and pipe, intercooler, and 3 pass radiator. So Heat Soak is NOT an issue. I'm also running the FACTORY thermostat. I do NOT have any tune installed, that is 100% factory. With the all season tires I run in the summer it's traction limited in 1st, 2nd, and some of 3rd on certain pavements so I just don't see a need for more power.

Note, in cold or cooler weather I do see about a 5 mpg DROP in fuel MPG while the engine is still cold. This thinking a colder thermostat should re-think that approach. Because that is simply a bandaid for an inadequate cooling system. Increase the radiator capacity and you'll not only see a gain in MPG's but you will also see a gain in power. This engine runs fantastic at 195 degrees and below or above that temperature there is a loss in economy and power. The Mountune 3 pass radiator allows the thermostat to maintain that temperature even when you are climbing a 7.5% 2 1/2 mile grade in I-64 heading into West Virginia in mid August.

So, here is what I am seeing for mileage. On level toll roads at 74 mph I will see 39 mpg. Driving on I-77 in WV I will see 34-36 mpg. Seems that curves, hills, and morons will impact fuel economy. In city driving my last fill up computed out to 33.2 mpg with an average speed of 29 mph. Note, tattletail was indicating 34.9 mpg, which is typical. I'll also not I only run 93 octane, feed this car 89 octane and it will cost nearly 5 mpg.
 


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