hpfp pressure drop suddenly at 5k rpm

that's good to know. thx alot!! We are very confusing and think the relief valve was not the problem. Since it built up pressure. Well, I am pretty it didn't hold up pressure all the way to 1850 psi. Time for a new relief valve!

 

We swapped the hpfp and fuel rail last night but it won't help. it still do the same thing. my friend found a bit of oil around the egr delete plug. There was some oil on the MAF. Could the MAF cause the problem? (since i looked at my datalog again that was before change anything, when the HPFP pressure dropped, the HPFP sensor voltage and MAF voltage dropped at the same time!!)

 

Fast forward almost 4 months later. After swapped the HPFP (both of our HPFP has autotech internal) and swapped the fuel tank with my friend. It was still having the HPFP fuel pressure drop issue after 5k rpm. After the weather got warmer in jun, I finally filled up full tank of 94 oct. gasoline and pushed it over 5k upto 6k rpm. No more fuel pressure drop issue...
I wonder if is it possible if there is boost cut from the cold weather to cause problem...? or is it possible there was bad gas in the tank to cause the problem?

 

Could be boost creep there after limits to prevent going to the moon.