My ECM is programmed for 24lb/hr injectors but I badly need to change them, can I use 26lb/hr ones or higher flow without reprogramming ECM?

 

What pressures are both injectors rated at???? Different brands rate at different pressures. A SVO 24lbs is 25.3 at LT1 pressure a stock 24lbs LT1 injector run at 39lbs is 22.7. "Same" size injetors are not necessarily the same. And if say the 26lbs are rated at 43.5 and the current tuned for 24s are rated at 39 then they are pretty close.

Why do you need to change them?

 

Why do you "badly need to change them"? Going from 24's (programmed at 24.9 #/HR in stock program) to 26's isn't much of a change, even if they are both flow rated at 43.5psi. The PCM can (sort of) handle it, but if you are maxed out on the stockers, you should consider something larger than the 26's.

The problem with going to a larger injector than the PCM is tuned for is what happens at WOT. In closed loop part load driving, the PCM can cut the fuel using the long term fuel corrections (assuming they aren't already bottom out for some other reason). But when you go WOT (PE mode) the PCM will not make the correction, since the long terms were cutting fuel. It just going to run about 5% richer.