Since you can test your fuel pressure then you need to test it after you shut down the engine.
You say it is 42psi with engine running, after you turn off the key watch the pressure, it should stay the same not drop down.
Yes 42psi is low for a '98, too low really, and a problem.
The fuel pump has a check valve built-in that prevents "back flow" when engine is off and also with pump running.
This is the only "fuel pressure" part of the returnless system, damper just absorbs pressure changes when injectors open and close.
There are also fuel line connections in the tank that can leak, this will lower pressure over all.
The fuel filter can effect pressure as well, as it gets clogged up the volume of fuel it can pass is less and less so pressure will go down, for $10 it is worth replacing every 4 or 5 years.
The computer expects 60psi of pressure, it has no way to monitor the pressure.
It opens the injectors for a specific amount of time to add fuel to the air in the intake based on 60psi pressure.
If pressure is lower than say 50psi then computer has to open injectors longer, to maintain correct fuel/air mix(O2 sensor data), the computer has pre-set limits for injector open time, if it reaches that limit and O2 sensor still reports lean exhaust then computer will turn on CEL(check engine light) to let you know there is a problem.
ECT sensor on the 2.3l(not sure for the 2.5l) is located on the drivers side of the block towards the front of the engine, under the intake.
ECT sensor has TWO wires, and tells the computer the engine temp, for cold(choke mode, open loop) or warmed up(closed loop, O2 sensors used)
ECT sensor looks similar to the Coolant temp SENDER, the sender has ONE wire that goes to the dash board temp gauge.
These two coolant temp devices are not connected together or shared.
Last edited by RonD; 09-07-2014 at 08:33 AM.