Roy Page wrote:

I bought our Piper Archer [PA28-181] just over a year ago from a Californian
owner and flew it home to it's new base in Ohio.
On the flight home, we noticed on long climbs that the fuel pressure fell
off from an indicated mid scale reading to about one third scale.
In level cruise the indicated pressure returned to mid scale.
Although we took the top cowl off at every stop to check carefully that we
still had all the important bits still hanging on, we failed to notice that
the gascolator had a slight fuel leak until a few days after we got the bird
home.
You need to remove the lower cowl to get access to the gascolator.
Our A&P put a new bowl seal on the gascolator which cured the leak and
appeared to cure the fuel pressure changes.
A few months passed and then occasionally I noticed a slight fall off in
fuel pressure when climbing.
I concluded that the mechanical engine driven fuel pump must be getting
tired and, to be safe, replaced it with a new pump three weeks ago.
No change, the fuel pressure still falls off when climbing and returns to
mid scale in level cruise.

Ideas please ?

I had lowish and fluctuating fuel pressure in an Arrow.
Turning on the electic fuel-boost pump would improve the pressure
and reduce the fluctuations.
Resealing the gascolator improved it a bit, but I was still worried.
Was considering replacing the engine-driven fuel-pump when my LAME
discovered that the the fuel-line out of the gascolator to the
electric boost pump had a crack.
He replaced that section of line and fuel pressure is now much more
into the green range with less fluctuations.