Question about fuel injection from a newbie

[Kdw1403]

What is maximum size fuel injector for a lt1 stocker engine. what pulse rat and duty cycle should i run them at? Having trouble with A/F ratio. Right now it is reading 14- 14.5. Never gets below 14. lots of low gear time reading 15. I have raised fuel pressure from 45 to 60 with no change in a/f ratio.30 lbs injectors now. I have been told that is really lean. New to Fuel injection. Has a fast xfi 2.0. can something be set wrong on the tune and cause the computer not to let it richen itself up. Running in closed loop now but same problem in open loop. Target is set to 12.8. closed loop high rpm is 2500 Low rpm is 2400. I just installed a fuel psi moniter to my data logger but havent got to run it yet. aeromotive a1000 pump. Anybody ever had this problem where you cant get A/F ratio to adjust?

[cmracing]

Originally Posted by Kdw1403

What is maximum size fuel injector for a lt1 stocker engine. what pulse rat and duty cycle should i run them at? Having trouble with A/F ratio. Right now it is reading 14- 14.5. Never gets below 14. lots of low gear time reading 15. I have raised fuel pressure from 45 to 60 with no change in a/f ratio.30 lbs injectors now. I have been told that is really lean. New to Fuel injection. Has a fast xfi 2.0. can something be set wrong on the tune and cause the computer not to let it richen itself up. Running in closed loop now but same problem in open loop. Target is set to 12.8. closed loop high rpm is 2500 Low rpm is 2400. I just installed a fuel psi moniter to my data logger but havent got to run it yet. aeromotive a1000 pump. Anybody ever had this problem where you cant get A/F ratio to adjust?

You will get opinions all over the place.

30lb/hr is ok for a 200-300hp engine, that is about it!

You should run at least a 42lb/hr, even a 55 or 60 will do just fine. If you want to play with injector timing you need far larger than "normal", but that's a discussion for another day.

I don't know what fuel you are running, but if it is C11 or C12, then a Target A/F of 12.6 is a good starting point, lean it out from there as you learn.

Make sure you are giving it enough room to do it's thing. IE: The Wideband Limits should be at least 50% until you get a decent fuel curve, then tighten them down to 5%.

Again, all systems are different, but they all do the same thing, just in their own ways. I use Holley for everything, but have used Haltech, Accel, Big Stuff, and FAST in the past. I prefer the Holley software over the rest of them, but they all work just fine.

[Painter]

I am thinking that if it is a new build it could be a plumbing issue.

[BRETV]

14-15 AF is too lean, I have run FAST for years, I think 30lbs are too small for your LT1 and the reason why when you jack the fuel pressure way up and doesn't change the AF is cause the duty cycle on the 30lb injectors is maxed out. If you look on your dashboard screen on your data logger( if it has the built in data logger and if it doesn't you need one) it will show you the duty cycle in %. And it shouldn't be over 90%




Bret Velde
2003 SS/LA

[countrypuppy4865]

30 lb injectors on Lt1 stocker are fine. As long as your duty cycle is less than about 80%, you have adequate sized injectors. More than likely your tune needs to be refined. Once it is optimized, then it will be close enough to adjust for air conditions if you are in speed density. Also, close loop needs to be enabled and configured if you desire to use that.

[Kdw1403]

Using renagade fuel, duty cycle is between 85-90 sometimes. Are there any draw backs to going to a 42lb - 50lb injector?. Not a new car just i am a newbie with fuel injection.

[Darrel Goheen]

Originally Posted by Kdw1403

Using renagade fuel, duty cycle is between 85-90 sometimes. Are there any draw backs to going to a 42lb - 50lb injector?. Not a new car just i am a newbie with fuel injection.

I just changed my 24lb injectors to 60lb over the winter in my Stock Eliminator LT1. I'm running 45 lbs fuel pressure. From all my research it seems it's best to run the fuel pressure at the injector rated pressure which is usually 43.5 lbs. Some people compensate for too small of injector by increasing pressure. Are you sure your O2 isn't being contaminated with an exhaust leak. Where is your O2 located?

[Signman]

Try replacing you O2 sensor they do go bad due to the leaded fuel. Also location should matter at low RPM but upstairs should not be a big influence unless you have a header leak, make sure there are no leaks at the flanges.
Raising fuel pressure should richen across the map but the ECU does not know it, it's best to add fuel by editing the table.
The internal data logger works pretty well for tuning when you indicate an area on the log open tables will show which cells are being used. Tables should have there dashboard closed for this to work. use percentage to make changes: the difference between actual and target O2 in percentage is added or subtracted from number in cell.

MOST Important: Always save your base file where you will not delete it.
Always save your tune with a unique file name when making changes (facility;date;run#). Much easier to go back where you were if the change did not work get lost which is easy.

You should be logging RPM, Fuel, Timing, O2, Voltage at least.
Cells are divided in RPM increment usually 500, in the data log select RPM range in high gear for a suspect cell. This will then give you averages on the dashboard below, have the fuel table open with its' dashboard off, cell being used in fuel map will be indicated. Make changes then make another run.

[Glenn Briglio]

How many and where are the O2 sensors located? Headers? Collectors sealed to primary tubes? What duration cam at .050?

[Kdw1403]

1 o2 sensor. Located in the collector up close to where headers slide in. Would 42 or 50 or even 60 lb injectors be ok to upgrade to?