None..No FP sensors..that is why there is the Test Port.
The FP regulator keeps the FP at a constant specified operating pressure so that the fuel supply to each injector is always the same. The amount of fuel to each piston/cyl is controlled by the electrical pulse width/time the injector is held open. That is ECU managements job and it uses many sensor inputs when doing these mix/load mapping calculations. The system is fully Electronic. If the fuel pressure is not at correct pressure spec zone to begin with, then you could get a Fuel Trim code b/c the ECU could not correct for FP too high or low..which is why one of the first checks with a fuel trim code is fuel pressure regulator.
[ the other being possible vac leak]
The mapping parameters of the ECU injector width sig needed to satisfy the required engine fuel demands are calculated by design with the known factor of the fuel pressure being in spec..this pressure is not controlled by ECU, it is a design spec of the fuel pump and regulator flow.[Fuel delivery system] The ECU simply EXPECTS that pressure spec to be maintained constant by that system.. and those specs are the ones I listed for you to verify with your TEST PORT and gauge chart. Those spec have to be verified FIRST on a suspected fuel flow complaint/diagnosis.............as you can see, if the Fuel Pressure is not kept in the spec zone at all times , then the AMOUNT of gas flowing thru an injector with a certain time width sig will be higher or lower than the engine is calling for b/c of too high/low of the FP pressure. The ECU can correct for this in a small % amount using it's sensors feedback Engine Management control system, but that has its trim limitations...One can easily verify this by taking a scope reading at the 02 sensor and watch that signal go instantly Overly-RICH by simply taking the vac line off the FP regulator..what has changed ??? nothng, except the fuel pressure has now increased beyond spec b/c of no regulation and that increase has allowed too much fuel to go thru the injector at the same injector open time...see what I mean??? [ look at FP chart and notice the pressure spec is HIGHER with vac line disconnected] This higher pressure test in included in the chart b/c that test is used to check the FULL capacity of the pumps/system, not the running/regulated pressure. Note that there are 3 test on FP..one is with regulation, one without, and then one for holding pressure. All must be met. The first two are with/without vac activation of Regulator and the last is check valve sealing/holding test at the pump outlet check valve . [ or leaking inj./lines/etc]
As far as OVP is concerned, the FP had nothing to do with OVP failure.
OVP is nothing more than a voltage spike protection device [ smart fuse] that uses Zenier Resistor/diode circuits to limit ECU voltage feed specs. Most OVP failures on that engine are manufacturer component defects and the new modified OVP will be sent to you when you order it.
The original over-voltage relay MB # 000-540-52-45 is to be be replaced with 000-540-67-45. MB issued info (internal bulletin) on that problem back in 1996
OVP can also blow from improper jump starting the car... a bad fuse will be indicated by ABS lamp, but a bad OVP does not always have a blown fuse , as that is an amp feed protection and not a part of the voltage spike protection circuit. I believe I posted that info for you before, which is what it turned out to be.
The FP relay turns on for 1-2 secs when the key is turned just to get FP to the rail of a car that has lost the residual pressure from long standing...your problem is the relay got NO signal from ECU once the engine had started ..that is where the ECU and rpm sig mapping come into play, but with no OVP feed to ECU, nothing would work .
That's about all I can tell ya.....
I can see you have an interest in understanding HFM/SFI system operation, so , for more technically detailed and accurate system specific info, you may want to check into the Service CD set ..these systems are in there and I think you can get one here ..see them sometimes on Ebay , too

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A Dalton