aftermarket exhaust causing MPG drop?

[mannydantyla]

My new-to-me 4Runner is awesome but the MPG sucks. I got less that 15 mpg (calculated at the pump) on the highway last weekend! V8, 75mph, AC on, 1" front spacer lift, driving into the wind. Yeah all those things add up to bad fuel economy, but it shouldn't be that bad, right?? On the way back, with the wind at our backs, the fuel economy was a little over 16mpg so it did get better.

Now I realize that the EPA says this vehicle gets 16 or 17 mpg on the highway so maybe that's just what it is, but I think that maybe it has something to do with the aftermarket exhaust that the PO installed.

Can anybody attest to this? The theory is that the freer flowing exhaust reduces the torque at lower RPMs because the engine needs that back pressure. I know this can be true because once I removed the muffler on my motorcycle to see how it sounded and the throttle response dropped terribly. I understand these are very different engines, but they're both 4-stroke and are governed by the same engine theories.

I don't know if I would swap the muffler for an OEM one because it really does sound marvelous, but I was wondering if I could chop off the resonator and weld on something with a little back pressure added to it. What do you think?

 

[Samm25]

I don’t know that the exhaust would cause the mileage to drop that much. Only if you’re flooring it more. I’m running true dual straight pipes. I’m only running the factory cats after the manifold and then everything after that is just straight pipes. I average about 17mpg on the highway with a 1.5” spacer and 265/70/17 tires with A/C on.

It’s possible it could be something else. I’d drop a can of 44K or fuel injector cleaners. Also check your spark plugs on the last time they were changed.

 

[cloud]

In the motorcycle world you shouldn't open up the exhaust unless you open up the airbox too. If you do both you may need to remap the ECU to get your performance back.

I'm not very well versed in these things and this is what has stopped me from doing the exhaust on my truck.

I run 31.5," tires with a 3.2-3.5" lift and I get 16.5mpg at 55mph and about 13 at 80mph

I agree that you should check spark plugs and maybe pull an injector and test it. Although varying your gasoline company every few tanks will keep the injectors healthy. It's very hard to foul an interesting from what I understand: bad gas will do it though.

Sent from my XT1710-02 using Tapatalk

 

[mannydantyla]

I get 16.5mpg at 55mph and about 13 at 80mph

Jeez, the aero on these 4runners is worse than I thought. I'm going to add an air dam, delete the mud flaps and running boards, delete the stupid "spoiler", add a front skid plate (mine is missing), anything to help the air slip by the truck better and with less wake.

 

[Rodtheviking]

My new-to-me 4Runner is awesome but the MPG sucks. I got less that 15 mpg (calculated at the pump) on the highway last weekend! V8, 75mph, AC on, 1" front spacer lift, driving into the wind. Yeah all those things add up to bad fuel economy, but it shouldn't be that bad, right?? On the way back, with the wind at our backs, the fuel economy was a little over 16mpg so it did get better.

Now I realize that the EPA says this vehicle gets 16 or 17 mpg on the highway so maybe that's just what it is, but I think that maybe it has something to do with the aftermarket exhaust that the PO installed.

Can anybody attest to this? The theory is that the freer flowing exhaust reduces the torque at lower RPMs because the engine needs that back pressure. I know this can be true because once I removed the muffler on my motorcycle to see how it sounded and the throttle response dropped terribly. I understand these are very different engines, but they're both 4-stroke and are governed by the same engine theories.

I don't know if I would swap the muffler for an OEM one because it really does sound marvelous, but I was wondering if I could chop off the resonator and weld on something with a little back pressure added to it. What do you think?

15 would be nice, I get about 11 to 12. lol

 

[doofenshmirtz]

Check your front brakes. I had the common seized caliper issue for a few months before I figured out. My mileage was at like 14mpg - I was basically riding my brakes everywhere... I lifted my 4runner in February, and found out the calipers were seized while doing it. Went to Napa and got their lifetime replacement ones, which are also already painted black to prevent ugly rust. When these seize up, I get to return them and get new ones indefinitely. I asked.

After adding the lift and redoing the brakes, I've gotten over 18+mpg many times, and have yet to get worse than 16.5mpg on a tank. All these numbers are calculated for my increased tire size against miles driven and gallons at the tank. I do drive like a grandma when I'm just commuting to work, though. Getting an alignment might not be a bad idea either.

 

[Inv4drZm]

Jeez, the aero on these 4runners is worse than I thought. I'm going to add an air dam, delete the mud flaps and running boards, delete the stupid "spoiler", add a front skid plate (mine is missing), anything to help the air slip by the truck better and with less wake.

The 1" front spacer could be doing more mpg damage than you think, keeping the factory stance front-to-rear (nose down) is probably best for mpg.

Don't forget to remove the stock roof rack as well.

 

[nevada]

75mph is why its so low.

though, the exhaust may add to that a bit. but, mostly because it sounds good, so people tend to stab the throttle more just to hear it.

I expect if you dropped the speed down slightly, you would see the mpg come up quite a bit.

 

[Trumpet]

The 1" front spacer could be doing more mpg damage than you think, keeping the factory stance front-to-rear (nose down) is probably best for mpg.

Don't forget to remove the stock roof rack as well.

Just removing the cross bars will yield 1 to 2 mpg improvement.

 

[FZRunner]

Removing mufflers and baffles will certainly lean out a bike and require an ECU mapping, nothing need be done about the airbox, but a modern truck will likely account for this change within a few cycles of the engine. Gas mileage should not be affected. I've done a fair amount of bike exhausts, and mileage stayed the same.