my 87 sat for a few years die to a bad LH, and dealing with hurricane florence dammage, etc. after sitting for 3 or so years, i finally got back to it. My son had tried to start it a few times (running when parked but had high idle after replacing MAF with one from Roger, i assumed a vac leak). i removed the plug at the fuel rail and pumped out all the old fuel and put a few gallons in the tank... now it starts and idles well, but dies when i give it any gas. i a, assuming this is a fuel starvation issue and possible a plugged filter, etc.. i used to have one of the gauges that went on the end of the fuel rail but cant find it now. my fuel injector pressure test kit does not have an adapter that fits the 928. any other way to test fuel pressure to confirm its a delivery issue?

 

did you get the LH rebuilt?
My 88 had a bad LH and after the intake refresh,
it would start and idle but die when the throttle was pressed.

I had a rebuilt LH installed as well as a fresh MAF.

Turns out the PO mechanic had also installed a new non Bosch regulator,
this allowed the alternator output to go to 18.5 V.
This in turn smoked the drivers in the freshly rebuilt LH.

NOTE if the car starts and idles then it stands to reason that it has enough fuel.

Have any of the dampers been replaced or the FPR?
its possible the damper and FPR could be swapped.

First step put your LH into a known good running S4.

Post a few pictures of the engine to make further guidance more accurate

 

you could disconnect the return line after the FPR and feed it into a container. then jumper the fuel pump and measure the output. IIRC you should get a minimum of 1350cc in 30sec. this would confirm fuel pump delivery as with the engine not running you should have 1ATM manifold pressure which would equate to max fuel pressure assuming the FPR is working.\ correctly.