Need help adjusting AFPR
Thread Starter
Drifting
Joined: May 2001
Posts: 1,295
Likes: 2
From: Surprise Arizona
Need help adjusting AFPR
I went to the track a few weeks ago. My best run was 13.1 @ 106 MPH. Stats from the runs are:
Temperature was in the mid 50's
R/T 1.438, 0.902, 1.021, 0.939, 0.880
60' 2.179, 2.153, 2.028, 1.914, 1.998
ET 14.062, 13.570, 13.557, 13.154, 13.284
MPH 102.03, 104.40, 103.73, 106.13, 106.32
I went and got a fuel pressure gauge today. The AFPR was set at 28 PSI at idle. Was the engine running lean? Damage? Pressure only went to around 35 at WOT. I am no expert here on tuning so help me out if you can. Doing some research in the archives I think fuel pressure should be around 45 PSI at idle correct? What is the correct way to set it and what pressure should I set it to?
This is an LT4 with Shorty headers, BBK T.B., K&N with cut lid, AFPR (set at 28PSI idle, 35 WOT during the runs), Power Effects exhaust. I dont know if there has been any tweeking to the ECM other than a 160 stat and the fans coming on sooner.
Thanks Guys.
Temperature was in the mid 50's
R/T 1.438, 0.902, 1.021, 0.939, 0.880
60' 2.179, 2.153, 2.028, 1.914, 1.998
ET 14.062, 13.570, 13.557, 13.154, 13.284
MPH 102.03, 104.40, 103.73, 106.13, 106.32
I went and got a fuel pressure gauge today. The AFPR was set at 28 PSI at idle. Was the engine running lean? Damage? Pressure only went to around 35 at WOT. I am no expert here on tuning so help me out if you can. Doing some research in the archives I think fuel pressure should be around 45 PSI at idle correct? What is the correct way to set it and what pressure should I set it to?
This is an LT4 with Shorty headers, BBK T.B., K&N with cut lid, AFPR (set at 28PSI idle, 35 WOT during the runs), Power Effects exhaust. I dont know if there has been any tweeking to the ECM other than a 160 stat and the fans coming on sooner.
Thanks Guys.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Both readings are too low.
Check the fuel pressure with the vacuum hose disconnected and plugged. 45/47 psi with the hose off and plugged would be a good starting point.
According to TPIS, GM increased the recommended fuel pressure on later year engines. I don't have the TPIS booklet in front of me, but your manual should show the recommended pressure.
When it comes to fuel pressure, it's always better to start a little too high than a little too low. Ignition timing is just the opposite.
Jake
Check the fuel pressure with the vacuum hose disconnected and plugged. 45/47 psi with the hose off and plugged would be a good starting point.
According to TPIS, GM increased the recommended fuel pressure on later year engines. I don't have the TPIS booklet in front of me, but your manual should show the recommended pressure.
When it comes to fuel pressure, it's always better to start a little too high than a little too low. Ignition timing is just the opposite.
Jake
Thread Starter
Drifting
Joined: May 2001
Posts: 1,295
Likes: 2
From: Surprise Arizona
Could the adjusting screw have backed out of the AFPR by Itself? I reset the pressure to 45 PSI as stated. I had to get a longer screw so I could put a jam nut on it to lock it in place. The car does'nt seem to perform any differently driven normally. One thing I do notice is the "wease" is gone. Before when I would shut off the motor it would wease as it stoppped running. It does'nt do that now. ???
What do stock injectors look like? Mine are basic steel cylinders with the top half painted black. No markings on them. What if the engine has bigger injectors on it? Would they have turned down the AFPR to compensate?
What do stock injectors look like? Mine are basic steel cylinders with the top half painted black. No markings on them. What if the engine has bigger injectors on it? Would they have turned down the AFPR to compensate?
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
The ECM will use O2 sensor readings to trim A/F when in closed loop mode at part throttle. So long as fuel pressure is within proper bounds the ECM can maintain stoch A/F ratio.
When you go to WOT the ECM ignores the O2 sensor and uses other engine parameters to index into stored data tables to set injector pulse width.
Soo, to set optimum fuel pressure you need some way to detect maximum power (dyno, drag strip, accelerometer, etc) and a scan tool to verify that fuel pressure is still within the bounds of the ECM to maintain stock A/F at part throttle.
Or you could just set it to 47psi and let it go.
When you go to WOT the ECM ignores the O2 sensor and uses other engine parameters to index into stored data tables to set injector pulse width.
Soo, to set optimum fuel pressure you need some way to detect maximum power (dyno, drag strip, accelerometer, etc) and a scan tool to verify that fuel pressure is still within the bounds of the ECM to maintain stock A/F at part throttle.
Or you could just set it to 47psi and let it go.
Thread Starter
Drifting
Joined: May 2001
Posts: 1,295
Likes: 2
From: Surprise Arizona
Originally Posted by REDC4CORVETTE
What brand FPR are you using?
"Quote from TPIS website
Adjustable Fuel Pressure Regulators
Since we introduced our Fuel Pressure Regulator in 1987, GM has adopted on the '88-'90 vehicles the fuel pressure that we have found to work well on the '85-'87's. For the '88-'90, we find that 49-52 works well and expect GM to follow our lead again. The LT1 fuel pressure is unusually high for the way the computer is calibrated. We are finding that, unless you send us your computer for reprogramming, you will be faster at 39 PSI, with a stock to bolt on modded engine. Installation time: 30 minutes. Lifetime guarantee. Emission-legal in all 50 states (EO Number 235-2).
/quote"
