Will the ECU be able to "self-compensate" for slightly larger injectors, say 24 or 26#? I am supercharged and need a little more fuel at full boost. I don't want to reburn my chip at this point if I don't have to.

 

The ECU will do the math, it's your mass-air meter that won't be right. In order to change injector size, you need a mass-air meter that is calibrated for the injector size you want. You also need to ensure your fuel pump will be able to supply the larger injectors, which is usually the culprit of top end fuel starvation. I am assuming since you have a blower, the kit came with an upgraded fuel pump of some sort, so I would suggest getting an adjustable fuel pressure regulator if you don’t already have one installed and a mass-air meter that is calibrated for the bigger injectors. 24# are the next size up from the stock 19# and unless you are exceeding 400hp, you don't need anything bigger.

 

ford makes a 30# that would be another choice.. dont know if it is true but i heard the computer will compensate about 10%. so a 20 or 21 # (good luck finding that size) might be ok but a 24 would not run to potential.

i think you can also make change in the chip. Seems like i saw someware that if you have a different airflow sensor or different injectors you cant use the new micro tuner. Im sure MIke can answer this question.

wonder what size injector the new 3 valve 5.4 will have?

 

Hi Mad,

No, the PCM will *not* just compensate on it's own for the change in injector size.

Doing that in the MAF's calibration, while that can work and sometimes pretty darned well, is not the "preferred" way to do this, as in the MAF's calibration the manufacturer is basically just doing a "divide by" so the load factoring (response to varying loads in certain areas) is not always right. Recalibrating the MAF is certainly the cheapest way to do this, and might work just fine for you, it just wouldn't be my first choice, that's all.

We also do not recommend using an adjustable fuel pressure regulator to raise rail pressure to inflate a smaller injector's fuel delivery capacity, because that provides more rail pressure *all* the time, thus the PCM (both the older EEC-IV's & the EEC-V's) will adjust in both closed and open loop, dialing that additional fuel right back out over time with shorter pulse widths.

We recommend using an adjustable FPR if you have a fuel pump or pair of pumps whose capacity is so large that you cannot get a decent idle, and need to back down the rail pressure to stock. For example, it's very typical with 255 l/hr. fuel pumps to need to use an AFPR to get the rail pressure back down to stock levels at idle, so the engine will idle.

AFPR's (adjustable fuel pressure regulators) certainly have their place and purpose, I'd be the first to agree, but we use them merely as a way to insure proper control over the rail pressure, usually set to within the stock parameters for proper operation with any mechanical configuration, and then size the injectors according to power demands. I'd never use an AFPR to increase rail pressure across the board to inflate smaller injector's fuel flow, for that matter you'd get a better result using an FMU to do that so that the rail pressure increase is not constant, but instead it's referenced to the actual boost & thus raised only when actually needed, for the most part, so the PCM doesn't get carried away dialing the additional fuel right back out.

In terms of how far you can go power-wise with the typical FMU that comes in a Magnacharger or ATI F-150 blower kit and the stock 19# injectors, you need to know the peak rail pressure with the FMU to determine that. For example, I don't like running more than about 80 PSI rail pressure at peak power (and ideally, I prefer to run stock rail pressure & use the cortrect sized injector, but either method works), though many FMU's will cause rail pressures in excess of 90 PSI at peak power.

At stock rail pressure in a supercharged 8-cylinder application, 24# injectors will support about 350 HP. WIth an FMU raising the rail pressure to say, a whopping 95 PSI, then the stock 19# units can potentially flow, at best, about equal to what a 30# injector would, & thus support about 435 HP on the motor. We have to remember that the BSFC goes way up in forced induction applications, in general you'll need 20% more fuel to make the exact same amount of power just from being supercharged, for example.

So to determine just how far the stock 19# injectors can be taken with an FMU, the first thing you must know is just what the rail pressures actually are at peak engine power. In general, with an FMU in say, a Magnacharger or ATI blower kit for the late-model F-150 you can usually support somewhere between 400 to perhaps as much as 435 hp AT THE FLYWHEEL, depending on just where the rail pressure ends up at peak power. However, it's not a good idea to *assume* that's going to be OK, at a bare minimum you need to see just how much rail pressure is really being achieved, and have the A/F's tested.

Before doing anything else, I'd recommend having your fuel rail pressure checked to see just what it is with the FMU (I'm assuming you're running an FMU here, of course), as *that* will tell you just how much power can be supported with your current setup. If you are within your power range, then it's just a matter of having the A/F's tested to make sure you don't have a tuning problem that is causing your complaint of needing more fuel at full boost.

You don't mention anything about how you determined that you actually need more fuel at full boost (so you may have already done some of this), and of course this is *far* too involved and important a matter to try resolving on these message boards, as nothing short of proper diagnosis & testing will actually determine what's going and what is needed, but I hope this information helps a bit.

The bottom line is, no, your PCM *cannot* just adjust or adapt to a change in fuel injector size on it's own, & I've pointed out the 2 basic ways to accomplish this (either proper tuning or a recalibrated MAF), along with recommending what is the preferable method, by testing the A/F's & retuning accordingly. If you go the recalibrated MAF route, *please* make sure to have your A/F's tested.

Good luck!