Or, he's enjoying all that newfound power and becoming a lead foot. :-)

Have him drive it gingerly for a bit and see if the mileage improves.
Eliminate the cheap options first. ;-)

On Sun, Jul 31, 2016 at 5:23 AM, Larry Alofs <lalofs@gmail.com> wrote:

> Hi Tom,
>    On a new installation I would assume that things like the air filter and
> spark plugs were installed new or at least inspected.  Was an OBDII plug
> included in the installation?  Check engine light?  If so, Autozone will
> read the codes for him.
>    The O2 sensor is one of the usual suspects for poor mileage.  With a DVM
> he may be able to monitor the signal voltage while it's idling.  It should
> go up and down from .1V to .9v or so.
>    Another possibility is blocked exhaust due to the inside of the cat
> breaking up.
>
> I would expect a bad cam or crank sensor to cause serious stumbling if the
> engine runs at all.  The MAF sensor or its equivalent might also be dirty
> or defective.
>
> Good luck,
> Larry
>
>
> On Sat, Jul 30, 2016 at 12:03 PM, Tom Stone <tstone8359@aol.com> wrote:
>
> > My son is driving his '84 Vanagon with a newly installed 2.5 Subaru
> engine
> > in it back from Colorado to Ohio.  He has noticed a decrease in fuel
> > mileage as he comes east.  He says it runs great and accelerates normally
> > but he is concerned about the mileage drop, from 22 to 16mpg so far.
> > Sounds like a sensor problem but I know nothing about Subarus.  Anyone
> have
> > any suggestions?
> >
> > Tom
> >
>