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Bad Fuel Economy. MPG decrease after mods

8K views 46 replies 17 participants last post by  Randi Ye 
#1 ·
I have the 2009 accord lx-s and I added a takeda sri and a magnaflow 14832 with no stock resonator. After that, I added Techron Concentrate Plus Fuel System Cleaner and I noticed that my mpg went down from 21 to 19. I drive mainly city. Any ideas why this happened? Is it possible there's a leak in the intake tubes or something?
 
#2 ·
Its most likely from you gassing it to hear the sound of your new intake and muffler.
 
#3 ·
I've driven it with just accelerating to only 2k rpm and I still get about 19 mpg in city.

Also I noticed that you have a magnaflow 14832. Do you have a resonator on it? If so, which one? I have the same muffler with no resonator but I plan on adding one.
 
#4 ·
Just drive all tank to red light fill up with new gas and you'll be alright MPG's came back to normal. I don't think its has something to do to any latest modification on your car. There's no leak in the intake tubes you will get CEL
Do not use again Techron Concentrate Plus Fuel System Cleaner . Here's a video on Techron
 
#10 ·
Intake mods will add more fuel, but exhuast mods just allow the car to breath better and if you actually make more power throughout the power and then it will save you gas because you'll make more power using less fuel. Lightweight pullies also will not make your car add fuel.

However exhaust mods are tricky. Sometimes you gain good power and also lose some low end tq. If you are only driving in the bottom of the rev range all the time and your exhaust has dropped your tq in that range. You will increase the fuel usage.

For example, on my cls when I did intake I didn't notice mpg go down really. Then i did pulley and full headers to the cAt. That increased my mileage by 2-3 for sure. At that point the car was getting incredible numbers. Then I did high flow cat. This made me lose a lot of low end and gain lots in the top end. So my mpg became worse than stock should be.

Therefore you need to be careful with exhaust mods.

On my current 08 v6 I have done the j pipe with 3rd cat removed and full cat back. And I don't plan on doing the hfpc because I feel it could lead to something similar.
 
#20 ·
Help! Fuel Efficiency Decrease

I have a 2009 accord lx-s with magnaflow 14832 and takeda sri. I noticed my fuel economy isn't too good. Combined mpg I get about 20 mpg with 60% city and 40% local. If I'm correct, my car should get ~24 mpg combined. Is there a way to fix this or should I take it to a mechanic for an inspection to see where the problem lies?
 
#21 ·
I have a 2009 accord lx-s with magnaflow 14832 and takeda sri. I noticed my fuel economy isn't too good. Combined mpg I get about 20 mpg with 60% city and 40% local. If I'm correct, my car should get ~24 mpg combined. Is there a way to fix this or should I take it to a mechanic for an inspection to see where the problem lies?
Randy, it all depends on how you drive, and on long you're in traffic, and how long you let your car idle when warming it up, and if you go through drive through food often where it is sitting idling. All those factors can decrease your view on supposed fuel efficiency losses.

Honestly, I've experienced horrible mileage solely on the account of hammering on the throttle, like 15 mpg, and great mpg cruising down I5 to Anaheim and keeping the RPM low and using cruise control got like 520 miles off a tank and only stopped to refill cause I was in the middle of the Grapevine late at night on my way back and didn't want to chance it since I didn't know how far til the next gas station and if there were going to be any unexpected delays. That 500+ miles was going all the way from Sunnyvale to Anaheim Hills, around that area for a few days, then proceeded to drive back and got about half way through the up portion of the Grapevine before I decided better refill.
 
#24 ·
Bad Mpg

My mpg is only bad on local but on highway I get about 29. In local, I get about 16-17 and I have a light foot on acceleration. I have replaced spark plugs and O2 sensor, maintained tire pressure and adjusted wheel alignment. Could it be that I need to replace the ignition coil or check the brake calipers to make sure its not scraping against the brake disc. Anything tips or points would be greatly appreciated. Thanks!
 
#25 ·
Depends where you are.True city NYC type driving you'll never get anywhere near the sticker mileage.Stop and go kills your mileage. If you're getting 29 on highway,it's not the motor.More likely,too many traffic lights,AC on,short trips.
 
#26 ·
6 shifter got it.

Try only using top teir gas. Google it to learn about it.

Also that video posted about the chevron techron is bad. No fuel additive cleaner will clean everything in one use. In the video it obviously worked but it'll take more uses to fully clean the engine. Using Top teir fuel limits carbon build up but using a cleaner additive here and there helps. I had 280,000 miles on my civic before the stock engine spun a bearing. I pulled the engine then tore it apart for parts and my injectors had zero gunk on them. I was so surprised that I pulled the injectors out of the new engine, just to see, and they where alil gunked up, so I just switched them. Later I pulled the head off and the pistons where pretty clean, way cleaner than the guy's in the techron video. Of course you'll have build up here and there, the idea is to limit it as much as possible.
 
#28 ·
Bad Fuel Economy

I have a 4 cylinder lx-s. I've replaced the O2 sensor and spark plugs recently but still getting 17 city and 21 combined mpg. I took my car to an auto shop and they couldn't find the culprit of bad mileage; they said everything was running fine. I also have a light foot so I was wondering what are my options here? I do want to fix my fuel economy.
 
#30 · (Edited by Moderator)
True but I get 17 in local. Even if it was all city driving, i feel like it would only be +/- 1 or 2 miles from the expected 21 city mpg.

How are you computing your mileage? Do you have an OBDII device (Scangauge etc) or are you just doing the gas added divided by miles driven thing? It seems hard to believe that your fuel economy is cut in half by city driving.
Doing it by the gas added divided by miles driven. Yeah it does seem hard to believe but that's what is happening and i can't figure out the problem
 
#31 ·
I was getting fed up with my car burning oil so I picked up some zmax fuel and engine formula.

I'm a burning wayyyyyy less oil now, if any (cause the dipstick is still reading full)

And I seem to be getting better fuel mileage as well.

I'd say it's worth a shot, it seems to have made a difference for me.
 
#33 ·
MPG Help

I originally had a takeda SRI and noticed that my mpg went down to about 19-20 avg. So I took it out and put back the stock intake box. I did several fill ups with 80% highway and 20% city and I get about 22mpg. I see that some people get mid to high 20's when they drive about 80% highway. I was wondering what else I can do to tune up my car to have it run better? I've done an oil change 2k miles ago, tires are all properly inflated, spark plugs were replaced and MAF sensor cleaned.
 
#37 ·
I originally had a takeda SRI and noticed that my mpg went down to about 19-20 avg. So I took it out and put back the stock intake box. I did several fill ups with 80% highway and 20% city and I get about 22mpg. I see that some people get mid to high 20's when they drive about 80% highway. I was wondering what else I can do to tune up my car to have it run better? I've done an oil change 2k miles ago, tires are all properly inflated, spark plugs were replaced and MAF sensor cleaned.
With regard to the reduced fuel economy with the SRI, that might have been caused by how the air moved past the MAF in the SRI tubing. The exact shape and size (bends) of the intake plumbing in the immediate area of the MAF will affect the air velocity past it and consequently affect the signal the MAF sensor sends to the ECU. Your SRI may have distorted the MAF sensor's signal and caused the engine to run rich, which hurt it’s fuel economy.

Now that you are back to OEM, your MAF signal is probably normal again. As for ways to improve your fuel economy, may I suggest you read up on hypermiling techniques? Unless your car is really old and has systemic wear-n-tear on it, it is probably running just fine. Your driving technique and driving environment will be the greatest determinants to good or poor fuel economy.
 
#36 ·
I would first verify your fuel trims by using a OBDII scanner, look at long and short term fuel trims. If they are much more than +/-. 8% then you need to find out why.

Sent from my Nexus 5X using Tapatalk
 
#41 ·
To decarbon the throttle body it needs to be removed then sprayed down with degreaser like simple green or gunk spray is better then wipe down thoroughly. It may take few times to do same process but the black stuff will come off. Remove as much as possible. Build up carbon is one of the reasons cars fail emissions test mechanics had told me. Agree it affects mpg as well.
 
#44 ·
The numbers are not that far off, so what those numbers mean is the ECM is removing fuel, compared to the base fuel map. The percentage is small, when you have major issues you will see fuel trims in the 20 to 30 range.

Sent from my Nexus 5X using Tapatalk
 
#46 ·
best way to increase fuel economy after mods is a TUNE.

I gained about 10-15% more mileage out of a tank after I got tuned. So basically the tune will pay for itself and using premium fuel is not really costing me any more money overall than if i were stock running regular.
 
#47 · (Edited by Moderator)
City driving in a 4 cyl heavy (3200+ lbs) car, constantly overcoming inertia is a recipe for poor gas mileage. I get about 16 - 18 in city driving, but adding highway will increase that to around 25 mpg. Pure hwy, around 35 mpg. It's all about Newton's law of motion.
I get the same as you 16ish for all city driving but doing all highway, I get around 30ish. I thought my car had problems but I guess not

If I get 31 mpg on all highway but only 15-16 mpg on all city driving on a 2009 accord I4 coupe, is that normal? In city, it's mostly short commutes with some hills
 
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