[itechteam]

2010 BMW 335i M - Misfires across all cylinders, when I start it at idle it starts at 2200 psi and will settle down to around 700 psi at idle. It runs very rough misfiring, I give it gas and it will drop some to 580 psi then up to 800 psi back to 600 psi.
I would think when pressing the gas pedal it would have a higher psi, this is in park.

I have ruled out coils and spark plugs, and o2 sensors. I am thinking HPFP, the car was tuned to stage 2+ and running a mix of e85 and 93 on stock HPFP.
Should I add pump gas to off set octane or replace HPFP?

[MoneyPitN54]

It could be injectors too. I'd check to make sure they aren't leaking before spending money on a HPFP. There's plenty of videos on YouTube showing how to do this. I checked mine out and realized it's worth getting an injector seal installation kit off fcp with all gaskets for a total of around $300. Expensive, yes. But better than spending $1,100 on a hpfp and being wrong. If your rail pressure dips below 600 in the way you describd, the loss of pressure is either caused by the HPFP not responding quick enough to build pressure, or the injectors sending too much fuel and the HPFP having to compensate for the excess loss of fuel pressure. Often times, if one part gets bad enough, it can stress the other to the point of failure. Best bet is to get definite answers with the $300 kit from FCP since those tools will be useful again if you plan on keeping the car for a while. Then if the injectors pass the leak test, it's time to replace the HPFP.