How much would would I need to curb fuel flow to run 30lbs injectors on stock programing? Here is my problem. I am planning a switch to an aftermarket computer in the near future but I have 30lbs SVO injectors on the way. I don't want to spend money on LT1 edit or programming since I am buying a new system anyway. These are going on a turbocharged but otherwise stock LT1. I thought perhaps I could lower the fuel pressure just a bit to help offset the size of the injectors. This would also allow my 8:1 FMU to have more room to ramp the fuel pressure based on the amount of boost I'm pushing into her. I could still get the fuel pressure to the max with the FMU anyway. The next question is, can you reduce the stock fuel pressure via the stock regulator, even if just a little bit or should I even worry about it and run rich under normal driving conditions?

The catch is I have to figure all this out before Saturday's dyno session. No pressure!

 

If these are 30# SVO's, flow rated at 39.15psi, you would have to turn the pressure down to 27psi to get them to flow the 24.9#/HR that is programmed in the stock PCM. If they are some other type, flow rated at 43.5psi, you would need to turn it down to 30psi. I can't think if any way you could accomplish that with a stock, non-adjustable FPR.

How long did you plan to run the stock LT1/turbo/FMU unit on the stock PCM/programming? Why not just wait and do it the right way, before you destroy the motor?

 

I went ahead and installed the 30lbs SVO injectors on stock programming just to see what would happen. The theory was that the computer would use the 02s to keep it from running very fat while under 75% throttle. When the computer enters P/E - Openloop mode, from what I understand, the computer ignores the 02s and runs on a prebuilt map. Based on the idea that the 30lb SVO injectors introduce about 22% more fuel for the same injector pulse width and fuel pressure, the math says this should put it close to where it needed to be but is still a little fat.

The car is running just fine and has about 30 more high boost passes on it. High boost is around 11psi on a stock engine. There is also an MSD booster pump assisting the stock intake pump.

 

Problem is the stock PCM bottoms out when the BLM's reach 108. That's only a 15% fuel cut, when you need closer to 30% cut, so there's still a good chance you are running rich and washing the oil off the cylinder walls, dilluting the oil, etc.

 

I did think about that. Giving it the most sophisticated testing I could, I checked the oil. I couldn't smell any gas in the oil and the oil didn't ignite when I brought a flame to it.

Another saving grace is the maf ends which are about a 1/4in larger in diameter than the stock. Maybe the engine is flowing say 2% more air than the computer is seeing in combination with the computer removing 15%. But the BLMs are around 125-130 at cruize depending on engine load. I have no explentation for that... I'll drive it around and reverify everything in the next day or so to get back to you just to make sure I didn't miss anything...

 

If your running overly rich you could wash out the cylinders, which is just not worth it. $50-$75 to get the PCM reprogrammed is a better option than premature wear.

Unless your car is a 93, you can't adjust fuel pressure and expect it to fix the fuel trims unfortunately.