More fuel pressure = better MPG?
05-29-2008, 05:39 PM
#1
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More fuel pressure = better MPG?
Hey guys, I just filled up the tank and I noticed something weird. Recently I replaced a fuel line and got my operating fuel pressure back up to spec, and I noticed my average MPG went up from 23 to about 25, and I'm sure thinsg will get better once I actually run a whole tank with proper pressure. This really doesnt make sense to me, as I would assume with less fuel pressure that car would burn less fuel, and that was reflected when I was on a dyno and had an A/F Ratio of 16.6. So what would make my mileage increase? More efficient engine operation? I'm puzzeled by this one.
05-29-2008, 05:49 PM
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Re: More fuel pressure = better MPG? (OMGWTFBBQ!)
i think your right about more efficient engine operation
i believe that the optimal A/F ratio is 14.7
i believe that the optimal A/F ratio is 14.7
05-29-2008, 05:50 PM
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Yeah, the best AF is between 13 and 14.5ish for NA and lower for FI applications, the dyno operator freaked out when he saw the AF. They actually had to spray my IM to cool it down between runs, my poor engine was running hotter than a George Foreman Grill.
05-29-2008, 05:53 PM
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Re: More fuel pressure = better MPG? (elektronsi)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by elektronsi »</TD></TR><TR><TD CLASS="quote">i think your right about more efficient engine operation
i believe that the optimal A/F ratio is 14.7</TD></TR></TABLE>
This is correct, stoichiometric = 14.7
i believe that the optimal A/F ratio is 14.7</TD></TR></TABLE>
This is correct, stoichiometric = 14.7
05-30-2008, 11:10 AM
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strictly speaking;
mpg is fuel burned.
less pressure = less fuel injected.
less fuel injected = leaner = higher mpg.
with your conditions I'd bet parts of your map were lean and other parts were rich. Or you pushed the throttle harder due to the lack of power that the leaner mixture produced.
those leaner mixtures require a bump in timing to keep the EGTs down.
mpg is fuel burned.
less pressure = less fuel injected.
less fuel injected = leaner = higher mpg.
with your conditions I'd bet parts of your map were lean and other parts were rich. Or you pushed the throttle harder due to the lack of power that the leaner mixture produced.
those leaner mixtures require a bump in timing to keep the EGTs down.
05-30-2008, 11:56 AM
#7
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Re: More fuel pressure = better MPG? (OMGWTFBBQ!)
except for the fact the a lean condition seen by the 02 sensor trys to compensate by longer injector pulses so not so good mpg. your theroy of proper engine operation is correct. any time a engine starts to wear or psi is lost on fuel the engine cant run as it was designed. mechanics will know this its the fuel trim pid on your scan tool. this is ultimatly the engines way of compensating for irregularites.
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05-30-2008, 01:07 PM
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Re: More fuel pressure = better MPG? (gsrhatch2356)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by gsrhatch2356 »</TD></TR><TR><TD CLASS="quote">except for the fact the a lean condition seen by the 02 sensor trys to compensate by longer injector pulses so not so good mpg. your theroy of proper engine operation is correct. any time a engine starts to wear or psi is lost on fuel the engine cant run as it was designed. mechanics will know this its the fuel trim pid on your scan tool. this is ultimatly the engines way of compensating for irregularites.</TD></TR></TABLE>
true, for OBD2 hondas.
For OBD1 hondas who do not have LTFTs, since you have an instant where it's lean then the ECU pulls the A/F back to normal (14.7 as per narrowband) you should see a increase in mpg.
true, for OBD2 hondas.
For OBD1 hondas who do not have LTFTs, since you have an instant where it's lean then the ECU pulls the A/F back to normal (14.7 as per narrowband) you should see a increase in mpg.
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