I have a 1991 MB 300CE. It has warm starting issues.

This has a 3.0L inline 6 with the KE-Jetronic fuel injection system.

If I drive it for 15 minutes or more, then let it set for 20 minutes, I will struggle to get it started again. It will fire off, but die immediately. Then long crank, it will keep popping and dying, but eventually start. When it does start, it will run very roughly for 10 seconds or so until it smooths out. After it has smoothed out, it runs just fine, no issues. Most of the time, not always, after sitting for 24 hours it will fire up without any issue the first time and idle at about 1100 rpm in warm-up mode.

I have replaced:
* Fuel accumulator
* EHA value (previous one was leaking from the valve itself, not the o-rings)
* Cold start valve / injector
* Fuel Pressure Regulator
* Coolant temp sensor

The full system pressure is reading 6.2 bar. Manual says it should be between 5.2 and 5.5 bar. Lower chamber pressure is 5.8 bar, so it meets the spec of being 0.4 bar lower that the full system pressure, but overall is out of spec. The system holds 3.3 bar of pressure for over 30 minutes, since replacing leaking EHA. Service manual calls for it to hold at least 2.8 bar.

I thought replacing the FPR would do the trick, but it did not. I know a FPR can only adjust so much pressure, so what is causing the addition pressure? I haven't tested the pumps themselves since it seems like they are healthy putting out more than enough pressure. I also don't have an adapter to hook them up to my meter. Could the issue be with the fuel distributor itself?

Thank you in advance!