W140 1999 Mercedes S420 Hard Start - Fuel Pressure Test and Diagnosis

In this video, I show you how to diagnose a hard start issue by using a fuel pressure gauge on a W140 Mercedes.
I have to replace the Fuel Pressure Regulator, so be on the lookout for that video in the near future.
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[@KurruptedDataYouT]

Did you ever fix this? Was it the fuel pressure regulator?

[@MileHighDreamz]

Yes. The aftermarket fuel pump I installed was making noise after some time so I switched back to the OEM but still had hard start issues when warm. I replaced the fuel pressure regulator (under the hood) and it starts right up every time. I would try that first