Stock Fuel Pressure Droops at WOT
#1
10 Second Club
Thread Starter
Stock Fuel Pressure Droops at WOT
I just finished installing a precision pressure sensor on my fuel rail and I thought some of you might be interested in seeing how the stock pump and regulator perform. I believe that my fuel system is in like-new condition. The sensor is a Measurement Specialties model MSP-600-100 and the data was recorded through an HPTuners EIO interface.
#3
10 Second Club
Thread Starter
The green line is a linear trendline drawn by Excel. The sensor was about $80 from Digi-Key. My fuel pressure is 59.2 psi at idle.
-Gary
-Gary
#5
10 Second Club
Thread Starter
Originally Posted by MeentSS02
That looks nearly identical to what I see for a pressure drop in my car using an Autometer gauge through the HPT EIO.
#6
10 Second Club
Thread Starter
An added note: At first glance, fuel rail pressure regulation of the stock system seems to be very poor, but since flow is proportional to the square root of pressure, flow will only vary about nine percent if pressure stays within the range 60 to 50 psi.
Trending Topics
#8
10 Second Club
Thread Starter
Originally Posted by BIG_MIKE2005
So then as long as you never see your gauge dip below 50 PSI everything is fine?
Last edited by Gary Z; 01-10-2007 at 02:57 PM.
#10
10 Second Club
Thread Starter
As MeentSS02 says above, you probably won’t eliminate the pressure sag unless you also move the regulator to the rails and install a full length return line.
#12
Kleeborp the Moderator™
iTrader: (11)
Yep...these are definitely the same thoughts going through my head...my idle rail pressure is 58 psi, and drops to about 52-ish psi by the end of the RPM range going WOT. I'll eventually swap out the stock pump for a Racetronix piece, and I'll think about running a full return line setup.
The only problem this poses is with the injector duty cycle...if the pressure drops, the injectors have to stay open longer to compensate. That's why I'm currently running 30-lb injectors (rated at 43.5 psi, so they are more like 34.6 or so lb/hr) on my stock internal car.
The only problem this poses is with the injector duty cycle...if the pressure drops, the injectors have to stay open longer to compensate. That's why I'm currently running 30-lb injectors (rated at 43.5 psi, so they are more like 34.6 or so lb/hr) on my stock internal car.
#13
TECH Fanatic
iTrader: (1)
yup, i've seen the same thing, even on upgraded hardware.
from what i've seen, it's not only MAP dependent, but also RPM dependent. once you combine them together, you end up with a very nicely direct relationship between fuel pressure drop and airflow.
http://redhardsupra.blogspot.com/200...-pressure.html
Gary, what kind of resolution do you get on the fp sensor?
from what i've seen, it's not only MAP dependent, but also RPM dependent. once you combine them together, you end up with a very nicely direct relationship between fuel pressure drop and airflow.
http://redhardsupra.blogspot.com/200...-pressure.html
Gary, what kind of resolution do you get on the fp sensor?
#15
10 Second Club
Thread Starter
Originally Posted by RedHardSupra
Gary, what kind of resolution do you get on the fp sensor?
#16
TECH Fanatic
iTrader: (1)
Originally Posted by MeentSS02
Marcin,
I still don't fully understand why the IFR table as it comes set in the PCM has values that go up with increasing MAP, while we end up seeing the opposite...was this done for a reason?
I still don't fully understand why the IFR table as it comes set in the PCM has values that go up with increasing MAP, while we end up seeing the opposite...was this done for a reason?
new version is pretty much done, just needs some cleanup, i fixed the labeling and it can calculate IFR from either estimated FP or the actual different FP vs MANVAC table if you can scan for it using a FP sender.
#17
Kleeborp the Moderator™
iTrader: (11)
Originally Posted by RedHardSupra
the injectors.xls that got so popular on this forum is not my work, i found it on the internet without credit. it had it (wrongly!) marked the pressure as MAP, not MANVAC which it should be--that's why you're probably 'looking at it the wrong way'
new version is pretty much done, just needs some cleanup, i fixed the labeling and it can calculate IFR from either estimated FP or the actual different FP vs MANVAC table if you can scan for it using a FP sender.
new version is pretty much done, just needs some cleanup, i fixed the labeling and it can calculate IFR from either estimated FP or the actual different FP vs MANVAC table if you can scan for it using a FP sender.