Help With Fuel Pressure Readings.
Thread Starter
Burning Brakes
Joined: Dec 2000
Posts: 849
Likes: 0
From: Lafayette LA
Help With Fuel Pressure Readings.
OK, stock LT1, runs a little rich most of the time - LT BLMs 122-124. I'm at sea level.
I hooked up a FP gauge and Here's what I got:
Before start = 41
At Idle = 38.5
At Idle with vacuum line removed = 43 (MAP was around 5 psi)
Under acceleration = 41
It was steady at each reading and never lower than 38.5. Am I testing it correctly? Are the numbers OK?
I hooked up a FP gauge and Here's what I got:
Before start = 41
At Idle = 38.5
At Idle with vacuum line removed = 43 (MAP was around 5 psi)
Under acceleration = 41
It was steady at each reading and never lower than 38.5. Am I testing it correctly? Are the numbers OK?
Burning Brakes
Joined: Nov 2000
Posts: 1,012
Likes: 1
From: Bowie MD
Re: Help With Fuel Pressure Readings. (olephart)
I finally installed the Accel fuel pressure gauge on the fuel rail, after the DYNO guy at Corvettes at Carlisle told me I was runnin rich by about 4 pounds. (11.5 air fuel ratio) He reccommended 12.5. Here is what I found. With vacumn line to AFPR disconnected/plugged. I was around 50 pounds. I backed the pressure to 46 pounds and reconnected the vacumn line and saw the pressure go to 56 with the engine running at idle. So I am concluding that the vacumn creates a higher fuel pressure. Maybe I have to try this again, and write it down. It seems to be the opposite of the original poster.
Melting Slicks
Joined: Aug 2001
Posts: 2,047
Likes: 0
Re: Help With Fuel Pressure Readings. (corvette1990)
Disregard the BLM stuff... the computer will find it's happy medium only after driving the car... you'll never get it figured out by the BLM because every car is different. The BLM takes the whole system into account (basically from the O2 sensor). Standard "factory" O2 sensors vary quite a bit and are realistically only intended to determine open vs. closed loop. I would take the thing to a dyno shop and make a couple back to back runs while monitoring A/F ratio. Unlike Carlisle, to do it right, an extra bung needs to be welded into the collector of the exhaust. The readings of the dyno's wideband O2 feedback will astound you. This is the only real way to set baseline fuel pressure for max power. From there? Custom chip tuning may be able to tweak it out if you've got extreme lean/rich areas throughout portions of the RPM range.
Thread Starter
Burning Brakes
Joined: Dec 2000
Posts: 849
Likes: 0
From: Lafayette LA
Re: Help With Fuel Pressure Readings. (EricVonHa)
So, corvette1990 has a pressure drop with the vacuum disconected and Vince and I have an increase.
Looks like I could still use some help here.
Looks like I could still use some help here.
Drifting
Joined: Mar 1999
Posts: 1,931
Likes: 1
From: Norcross GA
Re: Help With Fuel Pressure Readings. (olephart)
The vacuum is used to reduce the fuel pressure in the rail under regular driving conditions (high vac). It's basic use it the power shot you get when you blip the throttle. Like an accel pump. Vaccum drops - fuel pressure increases.
Least that is how the L98 setup works. Not sure about the LT or LS engines. The reg's are different, but the app should be the same.
Least that is how the L98 setup works. Not sure about the LT or LS engines. The reg's are different, but the app should be the same.
