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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...

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...

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!

yea i checked the relief valve with the key on method while the engine is still warm right after shut down the engine for more than 5 times. it built up pressure up to 1500psi mostly except 2 times it only built up the pressure up to 800~1000psi.... And my friend cleaned up the relief valve...

It actually wasn't too bad to drop the tank to swap my friend's tank (it only took around 2 hours to drop the tank from his ms3 and we did it on jack stands...haha...) i should put a new fuel pump and sock in but my friend's in tank fuel pump was working totally fine. So we just swapped the tank...

yea my friend said it can be possible too...he just want to make sure it is not the pressure relief valve before I spend the money on the pressure relief valve

I and my friend finally had a chance to swap the fuel tank from his ms3 to on my ms3 (he is going to do awd swap and his in tank fuel pump was working fine). however, it didn't solve the problem, it still got the fuel pressure drop at around 4.5k at full/75% throtte and it seemed getting worst...

I am going to swap the hpfp with my friend first before dropping the tank for the new in tank fuel pump/sock/regulator. Since when my friend changed the hpfp internal on my ms3, he told me that my hpfp was sticking and super dirty. maybe that's the problem (or another problem....)

updated tested spill valve and relief with koeo method, they are fine rev pass 5k without full throttle, the hpfp fuel pressure doesn't drop however, the fuel pressure is only 48psi before I start the car when the engine is cold...could it be my in tank fuel pump is clog or dying?!

it is on ap with ots stage 1+ map v2.60, cobb intake, TIP and cpe top mount IC

recently my 08ms3 had hpfp pressure drop problem. Before I changed the autotech hpfp internals, the hpfp pressure dropped suddenly at around 5.5k rpm under wot. Changed to the autotech hpfp internals and it started to drop the hphp pressure suddenly at 5k under wot. when the pressure drop, the...