My son is so busy he has no time to answer questions, so I am turning to the forum. I do some work on my own Legacy, but this is a friends 1995 Legacy runs great uphill but bogs down on the flats.  193,000. miles, new plugs, gas filter, air filter. I am thinking it is the fuel pump just want to confirm this.....or could it be a sensor?

 

 

So it runs well under heavy throttle, but hesitates or misfires under light throttle?

No CEL? Does the bulb work?

First thing I would check is any vacuum hoses, and the large hoses that attach to the intake tube. If any of those are loose or split it allows air into the intake behind the MAF sensor which will not be metered, and will cause the fuel mixture to be lean.

What kind of spark plugs were put in? How old are the wires? If the wires are old get new. Don't get the parts store cheapies. Get a decent set of wires, I've had good luck in my cars with Carquest house brand. I think they're made by Standard Ignition.

Knock sensors like to cause trouble on these and are easy to check. Search for my "knock sensor 101" thread.

Another possibility is a bad front O2 sensor. If its original (very possible) its time to replace that anyway.