A little backstory first, a few months ago I went to leave a store and my car took a lot of cranking to start, it actually took two attempts to get it to start which was immediately followed my a SES light, I did my due diligence and concluded with a trusty paper clip that I had code 54, low fuel pump voltage, at first I changed my relay with a NOS fuel pump relay and it seemed fine but still had long crank times, recently as my OCD got the better of me I decided to preventively change my fuel pump and sending unit (which was original), I already had the rear down to do springs and I bought the pump and sending unit last year “just to have on hand” i swapped in a brand new AC Delco pump, spectra premium sending unit, fuel tank vent valve, new rubber hose connectors and fuel filter, the first start was a long crank I figured was a given since it had to prime the fuel lines again, unfortunately I now have a persistent hard start and occasionally a slight high and rough idle (did a full tune up less than 100 miles ago) I put about 30 miles on the car of just around town driving, as I’m leaving the gas station it once again took two attempts of cranking to fire up and was followed by an SES code 54, where should I start? I’m assuming I should bust out the multi meter, anybody have any experience with this, once the cars running its very strong and responsive

 

The "54" indicates that the ECM detected the fuel pump circuit voltage remained below 2V for 1.5 seconds while still receiving distributor reference pulses.

That does NOT mean that the voltage at the pump was that low, and only that the voltage at pin B2 of the ECM is below that level.

I would suspect that if the voltage at the pump was actually that low fuel pressure would be inadequate to operate the injectors and the engine would stall.