Decrease in MPG with addition of 255lph pump

[Hawaii-50]

About a week ago my fuel pump went out and now I have a 255 (I plan on modifying the engine later on) with the stock non-adjustable FP regulator. At 1/2 tank with the stock pump I would be at about 122 miles. After the fuel pump fix, I only get 91 miles to 1/2 tank. I was under the impression that the FP regulator gives the engine only what it requires. My driving habits haven't changed, and I am wondering why my mileage has decreased so much. Does the 255 just spit out the fuel no matter how I drive it? I changed the plugs 2 weeks ago and will check the timing this weekend (if Hurricane Ivan doesn't pay us a visit). Any thoughts or suggestions?

Thanks-
Ted

 

[nito88stang]

You are correct. The FPR will only let thru what it is set for. Did you also change your fuel filter? When i changed my fuel pump, immediately my new filter got clogged. I noticed it right away because i have a fuel pressure gauge and it started reading lower. Check that.

 

[Hawaii-50]

Any other opinions?

Ted

 

[LX302]

Maybe you bent the float on the fuel sending unit when changing the fuel pump, making the gauge read a little lower.
Plus by measuring MPG based on the guage isn't a very accurate way to do it.
Fill up, mark the mileage, then run to half tank, fill up and mark the mileage.
Take the miles driven divided by the gallons used to fill the tank from half full.

 

[04sleeper]

I order to make sure you have the same amount of fuel each time to check mileage you have to top off your tank. Then the next time you get fuel top it off again and divide by the mileage. This is the only true way to estimate your mileage. It is a good habit to get into so you can keep your car running well.
If you do this and still find out you have a problem with decreased mileage then I would look to your stock FPR. The extra load of the 255 pump might have taken its toll on the diaphram inside of it and may have caused it to break.