Power loss above 2500RPM '96 Pulsar

[KayDat]

Hey guys, just asking for some advice here. My brother has a 1996 Nissan Pulsar, and it's got some problems. When the revs hit around 2500RPM, there is a smooth but sudden loss of power. If you keep your foot on the accelerator, the revs hold, but drop slowly but surely. If you clutch/put the car into neutral for a short while, the problem subsides a bit, but issue still kicks in at around 2500RPM. Does anyone have any idea what the problem could be? We just returned from the mechanics, and they couldn't find anything wrong with the car, or any error codes in the ECU. Thanks!

Edit: BTW, this happens in every gear, and at all throttle positions. There are no problems when engine braking though.

[Old Mechanic]

Check the fuel pressure. Put a t connection in the existing line and run a gauge to one of the windshield wipers so you can read the pressure when you are driving it down the road.

I would suspect several possible things but need to see what the fuel pressure readings are first, could be a partially plugged fuel filter, weak fuel pump, bad air flow meter, or throttle switch and several other parts so get the pressure reading before you start throwing parts in a hit and miss expedition.

regards
Mech

[jamesqf]

Something partly blocking the intake air path, like for instance a duct that collapses when it's sucking a lot of air, then springs back?

[mwebb]

connect your scope or DVOM to the 02 sensor signal wire
(black wire)
the two white wires are the heater wires and the gray wire is signal ground

drive the car at WOT when hot with the symptom occurring

what is the voltage on the 02 sensor signal wire
if it is low , around 100mv the system is lean - suspect something that will drive system lean like
LOW MAF sensor output OR low fuel delivery

if
02 sensor voltage is high around 850mv , suspect clogged cat
==================================
or the 02 sensor is FRAKED
===================================
can you get to FUEL TRIM values ? and Calculated load values in
the OBD2 system ?

[KayDat]

Sorry for the late reply, but here's some closure, and maybe for posterity/future Googlers: turns out it was a flaky air flow/mass meter (Old Mechanic was correct in one of his guesses). Got it fixed, so I thought I might as well post it here. Thanks guys!