hpfp pressure drop suddenly at 5k rpm

R

rzz001

Greenie N00B Member
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 fuel pressure sensor voltage dropped at the same time as well. I checked the relief valve with KOEO method, first time the pressure was raising slowly, second time the pressure was dropping slowly (both time the car warmed up already) so i don't know if my relief valve is holding which i will check it again. but other than the relief valve, what else i should look for? uninstall and recheck the hpfp? wiring?fuel pressure sensor and connector?
thx
 
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?!
 
Yes, it could be the in tank. I do not know what the pressure should be with just pump on but I am sure some in here do.

This is a drop in unit and an upgrade over stock.
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Fuel pressure out of the tank should be about ~65 psi. You might need to check/replace your intank regulator. (which sucks, sorry)
 
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....)
 
rzz001 said:
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....)
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you dont have to drop the tank, you can get at it from under the back seat if you go at it with a bit of tin snips.
ITFP hole.JPG
 
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. we swapped the spark plugs as well but it won't do anything either. my friend said he is going to take the HPFP apart again and double check/clean. Maybe swap the fuel pump reply and check the wiring as well. Btw, my ms3 didn't throw any cel (other than EGR code because of the EGR delete...haha)
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Bartosz said:
Hi,
Problem solved? it was HPFP? i've got same problem after 5K RPM, with full throtte fuel going down and got P0234 overboost.
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still no luck....we are still trying to fix it...but mine doesn't have any cel code other than EGR (EGR deleted)
 
Sho said:
I'd still bet on the relief valve if pressure is fine at idle and cruising
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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
 
It's a lot less work to replace the PRV then it is to drop the tank, you crazy. I hope you put a new pump and filter in while you had the tank dropped. Would be the perfect time and they are not a crazy amount of money.
 
JohnnyTightlips said:
It's a lot less work to replace the PRV then it is to drop the tank, you crazy. I hope you put a new pump and filter in while you had the tank dropped. Would be the perfect time and they are not a crazy amount of money.
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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 instead...
we r going to swap the hpfp and fuel rail and see which one is the problem...
 
Yeah, you coulda been done with this month's ago and saved yourself hours by just swapping the relief valve. It's a 10 min job
 
_Mazdarati said:
Why haven't you even checked the relief valve yet it's the easiest thing ever
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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 before he installed the autotech hpfp internal. maybe the relief valve was the actual problem (it may struck open sometimes and it opens too soon under high load??).
 
The crack pressure is 1850 psi for the relief valve. So if it's not achieving that pressure with the key on engine off test, before the pressure drops, you answered your dilemma.

Cleaning the relief valve does nothing .You have to replace it with a known working used one or a new one.
 
Sho is right. Your symptoms sound exactly like your RV starting to shit the bed. Just spend the money and get a new one. Even if it doesn't solve the problem, it's something that you will most likely have to replace anyways....
 
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