Question about fuel injection from a newbie
 

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?

Re: Question about fuel injection from a newbie
 

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.

Re: Question about fuel injection from a newbie
 

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

Re: Question about fuel injection from a newbie
 

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

Re: Question about fuel injection from a newbie
 

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.

Re: Question about fuel injection from a newbie
 

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.

Re: Question about fuel injection from a newbie
 

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?

Re: Question about fuel injection from a newbie
 

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.

Re: Question about fuel injection from a newbie
 

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

Re: Question about fuel injection from a newbie
 

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?

Re: Question about fuel injection from a newbie
 

Cam 268@50. No exhaust leaks anywhere

Re: Question about fuel injection from a newbie
 

I just made a street outlaw pass down the hi way in front of my house with data logger monitoring fuel pressure. I set it at 60lbs, left the line easy and got it in high gear real quick then nailed it. Data show instantly fuel pressure dropped to 25 and stayed there till I let off at 6700rpm. Pressure went right back to 60. Pretty sure its the fuel pump or filter. Since I am new to fuel injection is there anything else that can cause this? I don't think so but again I never thought thought a President would say that its ok for men to go into the womens bathroom. Thanks

Re: Question about fuel injection from a newbie
 

Listen to Cooter. Your injectors are big enough. You need to worry about your fuel pump, and filter. Your fuel pressure should not drop off like that. I use 36lb injectors in my Super Stock LT1, at 60 psi.

Re: Question about fuel injection from a newbie
 

I am really thinking that we might have a plumbing issue.

Re: Question about fuel injection from a newbie
 

Low fuel pressure at WOT is usually caused by a voltage drop at the pump, a failing pump or a pump too small to keep up with needed flow. A lot of people run a secondary hot wire to the pump that ensures proper voltage but can cause early electric pump failures. Definitely start by checking the fuel lines and filter. Also make sure you have enough fuel in the tank to cover the pickup.

Re: Question about fuel injection from a newbie
 

Now that you are logging Fuel Pressure, and you see that the pressure is dropping drastically, you have narrowed the root cause of the issue down to the fuel delivery system.
I personally think that 30# injectors running at their standard set pressure are borderline, but lets get your fuel delivery problem fixed first, and then, re-evaluate the injectors. Once you get the fuel delivery problem fixed, you will need to lower the pulsewidth numbers in your fuel table because right now, they are inflated from trying to compensate for the lack of fuel flow. Once the fuel pressure is constant, you will need to lower the pw numbers, which will bring your duty cycle down.
Think of it like this, at 25 psi, you injectors no longer flow 30# per hour. At 25 psi, they are more like 20#s per hour, so that's what you have at WOT.
Here's some simple math that applies:

The Fuel Consumption for this type of engine should be around .42 - .45#s per hr. If your engine makes 500hp, then it will need between 210 - 225#s per hr.

225 divided by 8 injectors = 28.125#s needed per injector.

If your injectors can flow a maximum of 30#s, and you need 28.125#s from them, then 28.125# divided by 30 = .9375 or 93.75% duty cycle.

If you raise the fuel pressure (and the fuel system is able to maintain that pressure at WOT), that raises the potential flow of the injector.
If your injectors are rated to flow 30#s at 45 psi, then they will flow around 35#s at 60 psi.

Now, you have 35# injectors, so the fuel you need - 28.125# divided by 35# = .80 or 80% duty cycle.

If I were you, I would fix the fuel delivery issue first. Then, I would upgrade to 36# injectors just to give you a little more margin for error.

Re: Question about fuel injection from a newbie
 

36 lb injectors flow 42 lbs at 60 psi. Smaller injectors at higher fuel pressure atomize the fuel better. Finer mist is easier to ignite. There is a reason the later (LS family) GM engines went to 60 psi.

Re: Question about fuel injection from a newbie
 

Actually the reason they went to 60 lbs.of fuel pressure was that the bean counters got involved in the cost reduction of the package...the horsepower was pretty much already there and it was a lot cheaper to raise the fuel pressure than it was to purchase Millions of bigger injectors to give you the same fuel volume....while a finer fuel mist IS easier to ignite the volume of fuel you are trying to burn is the same because you haven't changed the amount of air ingested and you are working with a specific A/F ratio...any horsepower increase is minimal but when working on 1 engine instead of Millions the cost is easily justified when any increase in power is good.....

D L Rambo....Stk 1300

Re: Question about fuel injection from a newbie
 

I have not had a lot of time to look at my fuel pump yet but i did turn the pump on and my meter says only 8.38 volts. surely i must be doing something wrong. I touched black to ground and red to hot while pump was running.Same gauge used on battery and battery reads 12.8 volts. what gives?

Re: Question about fuel injection from a newbie
 

Are you checking it with the engine running?

Re: Question about fuel injection from a newbie
 

Engine was not running.

Re: Question about fuel injection from a newbie
 

I don't know how your pump is wired. You may want to try checking with the engine running with alternator output.

Re: Question about fuel injection from a newbie
 

I unhooked wires from fuel pump. Hot wire reads 12.58 volts with battery reading 12.6. Engine not running. Changed ground of fuel pump from frame to battery. Still reads about 8.5 volts when I touch leads to fuel pump while it's running. If I unhook ground wire and check the hot wire while it is connected to the pump (pump is not running) the wire reads 12.58.I am a terrible electrical person so please forgive me if I am ignorant sounding.

Re: Question about fuel injection from a newbie
 

The LS1 Injector is a big improvement over the LT1 Injector.
I like the ability to change Fuel Pressure and Tune for Power.
Could not do that as well with the LT1 Injector.
Plus the LS1 is less prone to clogging and has a finer mist!
Believe the Ford 24# Injector works well too.

D

Re: Question about fuel injection from a newbie
 

No reason at all you could not alter tuning by altering the fuel pressure with the factory LT1 injectors. I know NHRA Stock Eliminator racers that do it all the time. Turn the fuel pressure up on an LT1 injector, they have a finer mist as well. That is the point. Higher fuel pressure atomizes the fuel better. That is the reason for higher fuel pressures being used. Better emissions is the main reason. Very small power increase are simply a bonus.

I use injectors from FAST in mine.

Re: Question about fuel injection from a newbie
 

Check the installation instructions for the A1000 to see if they can help.

https://www.aeromotiveinc.com/tech-h...-instructions/

Re: Question about fuel injection from a newbie
 

Maybe I missed it somewhere here. What size wires to the fuel pump? Have you tried a new wire from the battery to the pump and checked voltage? You could take the battery and make up leads that would go directly to the pump and check it, that eliminates all other wiring. Then start eliminating wires from there.

Sean

Re: Question about fuel injection from a newbie
 

I am irritated! I believe what your are saying. It makes sense. But Holley and Fast and some others say it's best to run fuel pressure at what the injector is rated at. On most injectors they are rated at 44.5 so I've got mine right at 45. I will raise the pressure next weekend.

Re: Question about fuel injection from a newbie
 

Injectors are flow rated at 43.5 psi, I believe.
Not sure why they would tell you that. I'm not the only one that found power there.
Listen to who you want to.
Or, test things for yourself.

Re: Question about fuel injection from a newbie
 

Yip your right. 43.5 not 44.5. Like I said I believe you and it makes sense. I'll be raising my pressure to 60 this coming weekend. Will you be at Topeka Nationals? Thanks.

Re: Question about fuel injection from a newbie
 

You can run any fuel pressure you want to within reason. Obviously, there are limitations on the low and high ends where the injectors will no longer function.

The only thing that is important is that you know what the injector flows at your new pressure. There are a couple of ways to do this, either using a mathematical formula to figure what it SHOULD flow, or, have one of your injectors flow tested at the new pressure.

Re: Question about fuel injection from a newbie
 

Are you in agreement that 60 lbs of pressure will offer better performance/fuel burning than 45 lbs.? My plan is to run 4 back to back runs Fri night. Two at current 45 lbs. pressure then change to 60, change fuel pressure in software and make two passes to see if it makes any noticeable change in performance. Thanks.

Re: Question about fuel injection from a newbie
 

I used the math, which showed my 36 lb (FAST) injectors would be 42 lbs at 60psi. I changed that, raised the fuel pressure, hardly had to touch anything else.

Darrel, you have to make the appropriate change to your ECU tuning. Just turn up the fuel pressure will make your car run very rich.

I'm not sure I will be at Topeka. I may be done.

Re: Question about fuel injection from a newbie
 

I do know that I have to change the pressure in the software as well as regulator pressure. Now as to whether I'll remember to do either one or both is another question. My brain fails me frequently it seems. Thanks again!

Re: Question about fuel injection from a newbie
 

Was Testing LS1 and LT1 Injectors
The LS1 Injectors misted better than the LT1 using same fuel pressure.
Couple LT1s Injectors clogged up causing fuel delivery issues.
So went with LS1 Injectors...direct replacement for the LT1's.

If you increase the Fuel Pressure and not Change the MAP.
They Injectors will only supply the fuel in the MAP.
May get a finer mist but the PCM would eventually relearn and provide the fuel the computer was programmed.

D

Re: Question about fuel injection from a newbie
 

That's actually where my 60 lb injectors came from that I put in my LT1.

Re: Question about fuel injection from a newbie
 

You are wasting your time and money unless you fix your power issues to your fuel pump. Raising the pressure will make things worse!

You should have a 10 gauge wire feeding the fuel pump. All the EFI cars I wire have a relay in the back, close to the battery, 20 amp fuse between the battery and relay. All wiring from battery to relay to fuel pump is 10 gauge. I also use a 4 pole battery disconnect switch. The smaller terminals on the switch are used to remove the power from the relay coil so when you hit the disconnect switch the engine stops immediately even if you have a working alternator (which I highly recommend you do).

I had a friend with a BS/A swap between 42lb/hr injectors and 60lb/hr injectors within 10 minutes for back to back passes. With keeping the A/F the same, the car ran identical. Don't listen to people telling you that large injectors are a problem.

Been doing this since 1986 and I'm not on here trying to solicit business. Several here know me. I don't have time or the inclination to take on any new projects anyway, just trying to steer you straight.

If you can't get and maintain 12.5 volts at the fuel pump park the car! Get a working alternator and that pump will be MUCH happier at 13.5 to 14.0 volts. So will the injectors.

Re: Question about fuel injection from a newbie
 

Wow! You have no clue. For one thing, MAP is Manifold Absolute Pressure.

Re: Question about fuel injection from a newbie
 

Why in the world would anybody think a B/SA car needed 60 lb injectors? That is forced induction stuff.

Re: Question about fuel injection from a newbie
 

I didn't think I needed 60 lb. 36 lb would be plenty. I only bought the 60 lb because I had a friend with a set that had very little time on them that he sold to me cheap. I think my LS1 has 42's in it.