Humboldtgrin

If all mechanical issues are fine I have found that Driving habits are usually what changes but not recognized or disputed. Also stop and go city vs highway driving ratio plays affect. Temperature also plays a key roll in fuel consumption. Colder weather=more fuel used. Also a change in usual max highway cruise speed or the direction of the wind will also have an effect of fuel consumption. And tire pressure too.

Thom

So it turns out so far that I was able to improve fuel consumption by splitting hair over the tiniest but unnecessary rich spots in my fuel model, but I am still 1 mpg down compared with the previous pump. Softening acceleration enrichment hasn't made much of a difference either.
I can certainly live without that extra mpg but I am slightly annoyed not really understanding where it evaporates, so to speak.
I checked the hardware as recommended but I was not able to notice any issue. Also fuel pressure at idle is a consistent 43.5 psi. Everything just works as it should... Go figure.

Humboldtgrin

Should fuel pressure at idle be lower? Is the manifold vacuum hooked up to the FPR?

refresh951

The job of the FPR is to maintain a constant fuel pressure across the injector regardless of manifold pressure. Therefore as manifold pressure increases so must absolute fuel pressure to maintain a constant fuel pressure (say 3 Bar) across the injector. Therefore fuel pressure is less at idle.

Alan 91 C2

Hi Thom,

One thing to keep in mind is that the actual fuel BTU content can change over time, depending what is actually at the gas station. The fuel you purchase today can have a different blend of ethanol or winter mix. The net result is your fuel mileage will vary substantially. I have seen my seasonal mileage vary over 10 percent, for similar driving and out door temps.