Wierd gas milage decrease.

[Deadhead]

Ok, when gas milage decided to go up to the outragous price's that they are at, i decided, maybe i should take it easy and not punch it up to 4.5k regularly.

So i decided that 3k rpm would be optimal for gas milage and getting around town.

Well, ever since i did that, my gas milage decreased pretty bad...and i'm at a loss as to why.

The only thing i can figure is there might not be enough back pressure from the exaust. Reason i say that is because i have rust holes on the piping and a muffler with a 3 inch diameter hole that has things falling out of it.

Could the lack of backpressure cause this problem? i know that my car sucks at lower RPM due to it, just there's not much torque at the bottom end, but after i pass 2.5/3k rpm, it really moves for a 4 banger.

[Deadhead]

anyone???

[superaccord]

hmm...don't really know bro...My gas mileage fluxuates as well. Last tank I got about 460/tank. This one I'm not sure of. But not that good. LOL...heres the funny part. I dont have 5th gear.LOL

[shepherd79]

well, leaky exhaust can cause that.
you may want to check the timing and make sure it is at OEM specs.
also, check your tire pressure. stock tire pressure is 28psi all the way around, but if you get them up to 32-35 psi you will get better gas mileage.
juch do simple check on tune up parts and make sure they are in good shape.

[Blkblurr]

do you still have your cat on the car? If so how old is it? Could be clogged. By the way, engines don't need backpressure. They need properly sized pipes to get the proper balance between gas velocity and ease of gas (exhaust) flow.

[Deadhead]

Uh... i've been told by a honda certified mechanic who worked at honda for 13 years as their lead technition that these engines rely on backpressure... but ok.

I don't know how old the CAT is because i've only had the car for about 12K miles or so.

[halxi]

Uh... i've been told by a honda certified mechanic who worked at honda for 13 years as their lead technition that these engines rely on backpressure... but ok.


and u was told by a honda certfied mechanic who worked for honda for 15 years that its easier to change a tranny on the floor... ive now decided everyone in colorado who has worked for honda is full of shit. Period. (im dead serious about this too, ask racerx, he'll tell ya)

Ive read so many different articles on backpressure, backpressure is NOT truely needed to achieve max performance.

Ive noticed that when i shift at 3k rpm my gas mileage drops way down, like 100 miles on half a tank? i think not!, so im going back to my usual run it up to 4500 then shift thing, i was getting 320 per tank off of that.

[T-Funk]

when my whole exhaust system fell off on my old accord the power shot through the roof but my mileage went from 600 km/ tank to 450km/ tank

[A20A1]

Uh... i've been told by a honda certified mechanic who worked at honda for 13 years as their lead technition that these engines rely on backpressure... but ok.


http://www.3geez.com/showthread.php?t=352
*** At the end of my thread I add my opinion on why backpressure would have been used.


Anyways next time your mechanic tells you that ask him to explain why...

I can agree:
Backpressure can be useful.

Backpressure is how exhaust braking works, though the restriction is added on purpose.

However:

Backpressure increases pumping work, the more pumping work the more power is wasted getting out exhaust gasses, instead of sending the power to the wheels.

Anything resisting the flow of the exhaust gas can create backpressure.

Restrictions like the catalytic convertor, chambered mufflers, and Pipe Bends are different then resctrictions like the pipe diameter.

While smaller pipes are a restriction, it aides in increasing exhaust velocity.
Now from that restriction is some backpressure, but backpressure is simply a side-effect of using a smaller pipe to get more velocity.

The problem is you want flow as well, in order to get more flow you need to increase the pipe diameter.

You want good flow and good velocity.

... Not good flow and good backpressure.

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[A20A1]

The only thing i can figure is there might not be enough back pressure from the exaust. Reason i say that is because i have rust holes on the piping and a muffler with a 3 inch diameter hole that has things falling out of it.

Could the lack of backpressure cause this problem? i know that my car sucks at lower RPM due to it, just there's not much torque at the bottom end, but after i pass 2.5/3k rpm, it really moves for a 4 banger.

You want to keep the pressure and heat of the exhaust in the pipe, if it's bleeding off through a hole prior to the exhaust exit, then your exhaust system will not be as efficient.

Plug the hole or remove the pipe from the hole-back. :ugh:

As for removing your exhaust or having it "Fall Off", well you basicly changed the distance to the exhaust exit. Much shorter, plus no restriction from the muffler or pipe bends, so you will free up some power in that way.

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[Blkblurr]

http://www.3geez.com/showthread.php?t=352
*** At the end of my thread I add my opinion on why backpressure would have been used.


Anyways next time your mechanic tells you that ask him to explain why...

I can agree:
Backpressure can be useful.

Backpressure is how exhaust braking works, though the restriction is added on purpose.

However:

Backpressure increases pumping work, the more pumping work the more power is wasted getting out exhaust gasses, instead of sending the power to the wheels.

Anything resisting the flow of the exhaust gas can create backpressure.

Restrictions like the catalytic convertor, chambered mufflers, and Pipe Bends are different then resctrictions like the pipe diameter.

While smaller pipes are a restriction, it aides in increasing exhaust velocity.
Now from that restriction is some backpressure, but backpressure is simply a side-effect of using a smaller pipe to get more velocity.

The problem is you want flow as well, in order to get more flow you need to increase the pipe diameter.

You want good flow and good velocity.

... Not good flow and good backpressure.

.
.
.

Yep. I agree

[FyreDaug]

I get better gas milage in the higher rpms, because I go through them faster. Rather than slowly accelerating at lower rpms, quickly accelerating is better for me because I dont use so much gas accelerating, its done quickly and I keep the rpms around 2k in town (whether than means using 3rd over 4th)

[Deadhead]

so basically your saying that my problem with abnormal power in the lower RPM range is not to do with my exaust at all?

So what the hell would it be?

I'm not getting much backpressure at ALL... there is little to nothing left in my muffler (things keep falling out LOL) and the piping is rusted to shit.... uh... other than the CAT. When i feel where the exhaust is coming out, i find several places, and they all have very little air flow...

[Oldblueaccord]

so basically your saying that my problem with abnormal power in the lower RPM range is not to do with my exaust at all?

So what the hell would it be?

I'm not getting much backpressure at ALL... there is little to nothing left in my muffler (things keep falling out LOL) and the piping is rusted to shit.... uh... other than the CAT. When i feel where the exhaust is coming out, i find several places, and they all have very little air flow...

I have the original exhaust and its full of holes my mileage has always been great. I dontthink that the problem.

How about some before and after mileage numbers to start??How long since your last tune -up?

Lugging it down it 5th and your gas pedal on the floor is not gonna get you good mileage.


wp

[Deadhead]

The last tune up was about 10k miles ago. However, there has been some stupid stuff done to it when they did they tune up. They didn't replace the wires, and they were bad... so i replaced them with some cheap one's at NAPA. Uh.... the air/fuel ratio screw has been messed with quite a bit, but i believe that it is in the right spot.

Also, i have a little bit of a rough idle sometimes, it will drop to where it will be really rough, then the computer will up the idle and smooth out just fine. Has new EGR, fuel injectors, TW sensor, plugs, wires, distributer.

Could the problem be something to do with the o2 sensor? i have one that i need to put on, a while back the computer came up with a code for the o2 sensor, but it went away and hasn't come back when i reset the computer.

I checked the mileage yesterday on that tank, and it was about 28 mpg, regularly i get approx 31mpg.

[Blkblurr]

where are the holes in your exhaust that you say don't have much flow? before or after the cat?

[Deadhead]

after the cat is where the holes are. I have some flow out of the 2 openings in the muffler, and most of it is really coming out through the pipe that comes after the CAT.

[Oldblueaccord]

The last tune up was about 10k miles ago. However, there has been some stupid stuff done to it when they did they tune up. They didn't replace the wires, and they were bad... so i replaced them with some cheap one's at NAPA. Uh.... the air/fuel ratio screw has been messed with quite a bit, but i believe that it is in the right spot.

Also, i have a little bit of a rough idle sometimes, it will drop to where it will be really rough, then the computer will up the idle and smooth out just fine. Has new EGR, fuel injectors, TW sensor, plugs, wires, distributer.

Could the problem be something to do with the o2 sensor? i have one that i need to put on, a while back the computer came up with a code for the o2 sensor, but it went away and hasn't come back when i reset the computer.

I checked the mileage yesterday on that tank, and it was about 28 mpg, regularly i get approx 31mpg.

28 mpg is really good all things considering.

O2 possibly could be going not really so sure how much it would have to do with gas mileage but id be interested in how you made out if you changed it.


wp

[Blkblurr]

If the cat is clogged, you will have less power and lower gas milage. The loss of power is more noticeable at lower rpms. I don't really know how to check it though. Any way you do it it's going to take as much work as replacing it.