[MontieShaw]

Hey everyone, im curious if you can help me out. I just installed pypes high flow cats and pypes off road H pipe on my 2005 Mustang GT and now my average mpg is around 40 when driving. That cant be right. I already had pypes violators on my car and it never did this before. There are only two seals that leak and its at the front (towards the engine) of both cats. Nothing else as far as i know leaks. How are MPGs calculated? Could it be an O2 sensor went bad, or could the 2 leaks I have right before the cats be causing this? Any thoughts you might have would help me! Thank you!

NOTES: I drove roughly 50-100 miles with the O2 sensors in the downstream holes just before the cats while i waited for my O2 extentions to come in, it wasnt until I swapped my O2 sensors to behind the cats that the Check Engine Light came on, but i reset it by unplugging my battery because i though moving the location could have caused it. I did that yesterday and It hasn't come back on since.

We did need to remove the passenger side exhaust header/manifold because the manifold stud broke during removal of stock midpipe. Just to clear things up, O2 sensor locations are as follows, driverside upstream O2 sensor is on the exhaust manifold, passenger side upstream O2 sensor is on the down pipe halfway between manifold flange and catalytic converters, catalytic converters are imediately after the downpipes bend from vertical to horizontal, downstream O2 sensors are on the rear side of the cats. If there's any other questions i'd happily answer them!

 

[geraldcash20]

I find that is awesome but cant be real to get 40 mpg ? Anyways if it was still legal for me to do the long tubes and the high flow cats I would do it but yeah I don't have the money for that stuff yet. Some thing I will do when I have the mustang paid off maybe if you are getting 40mpg lollawl.gif

 

[Stella09]

Are you calculating this out manually or going by what the computer says? I highly doubt you are anywhere close to getting 40mpg.

 

[msirach]

The mpg is a calculation using data from injector pulses usually. If your looking at the instantaneous, it is a phantom number. Your tank average is the real story.

 

[jlee910]

Calculate it by hand. I removed the cats from my Honda VTX 1800 motorcycle and went from 21 mpg to 33, so it can make a huge difference, but I doubt you're seeing 40. Maybe mid to high 20s if I had to guess.

Fill your car all of the way up, reset your trip, and run ~3/4 of a tank out. Fill it all of the way back up, and divide the trip mileage by the number of gallons it took to fill.

 

[MontieShaw]

Thank you guys for replying, this is the average mpg not instantaneous mpg thats reading 40mpg. I was wondering if anyone could tell me why it would be showing a mpg that i know im not getting.

 

[08_TVS_GT]

You're missing a decimal somewhere...

 

[JBert]

I hope it is not running super lean due to some issue with the O2 sensors, that could be really bad . . . but I doubt that is the case because I would think that it would run like crap if it was. I think I would go easy on it until I got it figured out.

Like the other guys said, do the math the old fashioned way and see what that says. (Fill up the tank; measure miles traveled; fill up again; divide miles traveled by number of gallons to fill up.)

I don't know how the computer measures fuel consumption; it could be from the injector pulses like msirach said; but I doubt the O2 sensors have anything to do with throwing off the fuel consumption number in the computer.

It is possible to get real high average MPG readings, depending on when you reset it. For example if you push reset while coasting down the highway, you will get very high "average MPG" for a while, until you do some normal off-highway driving to bring down the average.

 

[JonR2006]

If you unplugged your battery that will reset all mpg data and will start fresh. This happens in our 09 malibu, when I unplug the battery for whatever reason, it takes a couple tanks to even out both average and instanteous milage. It reallys screws it up if you are driving very conservatively and/or a lot of highway mileage. Calculate it by hand and get an accurate reading. There is not way on gods green earth you are getting 40mpg in a mustang GT