So, I ran some flow tests for the fuel system. I disconnected the return line and routed it into a fuel canister. Then I ran the car for about 2 minutes and measured the fuel amount. I did not account for the fuel consumed by engine since it's not much of the total. I did the test with 3 Bar and 5 Bar fuel pressures. Here are the results:
258 lph @ 3 Bar (320 lph)
200 lph @ 5 Bar (263 lph)
Values inside the parenthesis are ones reported by the manufacturer.
At both pressure levels the flow is down about 20%. During the test the pump was seeing more than 13.5V at the terminals so it's not an electrical issue. Could be a bad pump or just too restrictive fuel lines (for the pump of this size). I haven't measured the pressure at the pump outlet but I suspect it would be higher.
This all combined with a china
FPR which most likely is letting too much fuel through, lower pump voltage and heated fuel would explain the problems we had at the dyno.
Edit:
I also checked the pressure at the outlet. Pressure at
FPR was 3 Bar. The gauge at pump outlet showed over 4 Bar. I've previously verified that gauge reads the same as the fuel pressure sensor. So that's over 1 Bar pressure drop between the pump outlet and the
FPR. At slightly over 4 Bar, the pump should do 287 lph so actually it's not doing that bad.
Edit2:
Checked the pressure in the engine bay, right before the filter: 3,4 Bar. So that's a 0,7 Bar drop from the pump to the filter. The rest 0,4 Bar comes from the filter and fuel rails.