Loss of MPG

[mrb93cb7]

my accord used to get over 420 miles per tank. After owning the car for a small period of time and have done a few small mods(cold air intake,ebay headers) , but the mpg on has dropped to about only 300 mile per tank. I'm kinda mind boggled by the drastic cut in fuel economy. I tried all that i know from replacing wires spark plugs, rotor cap and button to fuel filter and adding premium to see if that makes a difference. Does any one have an idea on the topic?

[deevergote]

Premium won't do anything at all for you. "Premium" is misleading. It's not better, it just has a higher octane rating to discourage detonation on cars with higher compression, high redlines, and forced induction.


Anyway, airflow mods generally cause a loss in fuel economy. Intake mods result in more air (therefore oxygen) moving into the engine. The o2 sensor reads this increase in oxygen, and the ECU dumps more fuel to compensate. By properly tuning an ECU, you can increase both power and fuel economy... but a stock ECU doesn't really know what to do with mods. Opening up the exhaust results in an increase in high rpm power, at the expense of low rpm power. Therefore, you're likely revving higher and pressing the gas harder to compensate.
Additionally, your o2 sensor may be old and failing. It won't always throw an error code right away. Replacing it with a proper replacement may help (Denso or NGK/NTK ONLY... no Bosch, they don't work.)

Is your check engine light on, by any chance?

Have you been carrying anything heavy in the car recently? I was in a band a few years ago, and I got tired of taking my gigging equipment out of my car during busy show months... so I just left it in the trunk and back seat. An extra 100-200lbs of crap made a HUGE difference in my fuel economy.

The decrease in fuel economy may also be tied to your driving style. Add "go fast" parts to a car, and very often you don't want to drive like a granny anymore!



Finally... it's "header", not "headers". We only have one.

[mountaineerjeff]

like deev said, I always find the biggest culprit to be the driver. normally when mods are added cars are driven harder.

another issue to check would be the possibility of a vacuum leak or even exhaust leak. either can upset the stock ecu and cause MPG issues.

the best way to tell if its you or the ecu would be to check the plugs to see if its rich and dumping fuel

[94EGCoopey]

Premium won't do anything at all for you. "Premium" is misleading. It's not better, it just has a higher octane rating to discourage detonation on cars with higher compression, high redlines, and forced induction.


Anyway, airflow mods generally cause a loss in fuel economy. Intake mods result in more air (therefore oxygen) moving into the engine. The o2 sensor reads this increase in oxygen, and the ECU dumps more fuel to compensate. By properly tuning an ECU, you can increase both power and fuel economy... but a stock ECU doesn't really know what to do with mods. Opening up the exhaust results in an increase in high rpm power, at the expense of low rpm power. Therefore, you're likely revving higher and pressing the gas harder to compensate.
Additionally, your o2 sensor may be old and failing. It won't always throw an error code right away. Replacing it with a proper replacement may help (Denso or NGK/NTK ONLY... no Bosch, they don't work.)

Is your check engine light on, by any chance?

Have you been carrying anything heavy in the car recently? I was in a band a few years ago, and I got tired of taking my gigging equipment out of my car during busy show months... so I just left it in the trunk and back seat. An extra 100-200lbs of crap made a HUGE difference in my fuel economy.

The decrease in fuel economy may also be tied to your driving style. Add "go fast" parts to a car, and very often you don't want to drive like a granny anymore!



Finally... it's "header", not "headers". We only have one.

In all honesty, this is post is all you need.

In addition, check your cat for clogs.

And I prefer Denso's, NEVER BOSCH's.

[cb7 calling]

In addition tire pressure. Seriosly though 300 miles per fill up is about 26 miles to the gallon depending on when you fill up. The epa figures for your car in 1993 where 22/28 city/highway I believe. In the summer I get 31 mpg in the winter I get 26. The car has to warm up in Ohio. That's about equal to 400 vs 300 per fillup. Your talkin 3 maybe 4 mpg. Could be anything.

[blucb7]

have u had a recent oil change? i find when my oil starts to dirty i can really hear and feel the difference in the engine

[mrb93cb7]

loss of mpg

ok im very pleased to see how quickly this forum site works. i can agree with the lead foot issue i do occasionally push it sometimes, but for the most part i drive it easy. I replaced the o2 sensor when i installed the "header". It has been idling rough these last couple of months and has been getting worse. Iv done a complete tune up and yes i even changed the oil. I was told by a friend that it could be the TPS sensor and that could of been the problem, any advise on that? My goal was to achieve a lil more power thinking under the assumption that more power would equal better mpg due to less strain on the motor but to a point didnt know something as simple as a cold air intake would throw it off. As you tell im a lil new to this

[Tippey764]

Premium won't do anything at all for you. "Premium" is misleading. It's not better, it just has a higher octane rating to discourage detonation on cars with higher compression, high redlines, and forced induction.


Anyway, airflow mods generally cause a loss in fuel economy. Intake mods result in more air (therefore oxygen) moving into the engine. The o2 sensor reads this increase in oxygen, and the ECU dumps more fuel to compensate. By properly tuning an ECU, you can increase both power and fuel economy... but a stock ECU doesn't really know what to do with mods. Opening up the exhaust results in an increase in high rpm power, at the expense of low rpm power. Therefore, you're likely revving higher and pressing the gas harder to compensate.
Additionally, your o2 sensor may be old and failing. It won't always throw an error code right away. Replacing it with a proper replacement may help (Denso or NGK/NTK ONLY... no Bosch, they don't work.)

Is your check engine light on, by any chance?

Have you been carrying anything heavy in the car recently? I was in a band a few years ago, and I got tired of taking my gigging equipment out of my car during busy show months... so I just left it in the trunk and back seat. An extra 100-200lbs of crap made a HUGE difference in my fuel economy.

The decrease in fuel economy may also be tied to your driving style. Add "go fast" parts to a car, and very often you don't want to drive like a granny anymore!



Finally... it's "header", not "headers". We only have one.

In all honesty, this is post is all you need.

In addition, check your cat for clogs.

And I prefer Denso's, NEVER BOSCH's.

Except it misses an easy to check area that could cause serious drop in MPG

OP check you brakes and make sure none of them are dragging. Re lubricate all of your slid pins and clean all of the hardware ( or replace it )

[94EGCoopey]

ok im very pleased to see how quickly this forum site works. i can agree with the lead foot issue i do occasionally push it sometimes, but for the most part i drive it easy. I replaced the o2 sensor when i installed the "header". It has been idling rough these last couple of months and has been getting worse. Iv done a complete tune up and yes i even changed the oil. I was told by a friend that it could be the TPS sensor and that could of been the problem, any advise on that? My goal was to achieve a lil more power thinking under the assumption that more power would equal better mpg due to less strain on the motor but to a point didnt know something as simple as a cold air intake would throw it off. As you tell im a lil new to this

A cold air intake will not cause this. Atlesst I have never come across one.

To check your tps, you will need a DMM aka digital multi meter. I am unsure of the specs off my head. Should be in the FSM.

[deevergote]

A cold air intake would result in more oxygen in the intake charge, therefore causing the ECU to dump more fuel... but not a terribly significant amount.

The TPS would throw a CEL.

[cb7 calling]

Beyond a rough idle does your car hesitate anywhere in the 2000 to 4000 rpm range? If so distributor.

[deevergote]

Or o2 sensor.

[94EGCoopey]

ok im very pleased to see how quickly this forum site works. i can agree with the lead foot issue i do occasionally push it sometimes, but for the most part i drive it easy. I replaced the o2 sensor when i installed the "header". It has been idling rough these last couple of months and has been getting worse. Iv done a complete tune up and yes i even changed the oil. I was told by a friend that it could be the TPS sensor and that could of been the problem, any advise on that? My goal was to achieve a lil more power thinking under the assumption that more power would equal better mpg due to less strain on the motor but to a point didnt know something as simple as a cold air intake would throw it off. As you tell im a lil new to this

When's the last time you checked plugs or replaced wires.

[mrb93cb7]

i bought a new TPS sensor to be safe and great thinking on the brakes. The rotors are way beyond repair and definitely needs to replaced. When brakes applied, they rock the car unless you use the brakes and down shifting at the same time. In which is what i have been doin to avoid the whole car shuttering. The car needs a lot of work done to say the least. maybe that could be where the extra consumption is coming from? Besides the occasional lead foot.

[deevergote]

So you've been downshifting to help stop the car... meaning the engine revs up high each time you brake. That'll have an effect on fuel economy for sure.