gas mileage down 10% after switch to Flowmasters?

[Mitch Alsup]

I say: "Get thee to a dyno" so you can measure the exhaust gasses and figure out if you are running rich/lean and then bring the fuel pressure to the proper pressure so that the computer can figure out where to run the engine.

Once you get outside of the range where the ECU can return the engine for emissions and performance (mostly emissions) the ECU can simply give up and run open loop. Most ECUs run open loop at WOT, you run WOT on the dyno, so setting the fuel system right on the dyno will bring the engine back to the point where the closed loop system can control the engine properly.

 

[02supercrew]

quote:

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Originally posted by crw:
Thanks for all the responses. These are the Delta-50's, so they're not the all-out race mufflers. They were professionally installed by a local guy that's been around forever and has a great reputation.

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I have the Delta 50 SUV DIDO on my '04 F150 5.4L. What a great sounding muffler.

FWIW, make sure that the muffler was installed in the correct direction....There is a difference!

 

[Mr Nice]

Are you guys still getting winter gas up where you live ?? Maybe an O2 sensor is going bad ? Time for a tune up?

I had 2 chamber Flowmaster mufflers on a 5.0 Mustang (no cats with shorty MAC headers) and my gas MPG DID NOT go down.

Hi flow mufflers *should* NOT hurt your gas mileage in any way since it is a 'Cat-Back' system.

Today I got Borla mufflers on my Vette.....and no drop in my MPG either.