That is only true if the tune was done using the PE or IFR tables. If the tune was properly done, all you need to do is properly update the IFR table and the fueling will be correct. You will need to verify how much to change the IFR based on the specs from the injector manufacturer, they also should provide the minimum pulse width, offset injector time, injector turn on time, and some other details that will help adjust the PCM for the new injectors proper operation. Doing the tune the proper way will ensure you will not be rich , unlike the IFR or PE only tunes. Good luck and I totally agree with Marcin (redhardsupra).

 

well, it turns out when you change injectors, IFR is not necessairly the only table to change. i'm in the process of obtaining hardcore info on more different types of injectors, but it's not here yet--these things will alter things like offsets and minimal pulses, etc.
what i'm talking about here is that bigger injectors will need more fuel total delivered to them. that's when the pump/lines/regulator become a problem. usually what happens, at higher rpm the fuel pump just runs out of its capacity and starts to drop pressure as the result. the problem with that is that we're not accounting for that extra pressure drop, and then IFR table does not account for the deminished flow. if that happens, we're basically back to the IFR hacking methods, which is a shame. the only way to run around it is to measure fuel pressure at manifold vacuum and rpm values, and come up with a fully custom IFR table particular to your setup. or just get a fuel pump that's well matched with the injectors so the fuel pressure drop doesn't happen, which allows us to keep the 'official' IFR shape/values.

all of this, with a lot of mad examples been described on my site:
Under (Fuel) Pressure
IFR spreadsheet for Logged Fuel Pressure
Fuel Pump sizing
VE-IFR transformation

happy many hours of reading

 

See, I told you he knows his ****.

I need a smiley w/ smoke coming out his ears.

 

Adam1803, PM your tuners info. I think I know who you are using (in your area). I know someone in Pensacola (my tuner). Might be worth the drive but he uses EFI Live.

 

I agree and would also like to add that Voltage drop was an issue for me in my scans. Turns out that when the meth pump kicked on I had a leveling of the voltage supply to the fuel pumps, not enough to show a drop in FP but just enough to flat line it for a second (boost referenced FPR). This gave me a less than commanded AFR at around 4500rpm. Took me forever to find that one

 

yup, you're completely right, i forgot about it because the one car i got the most data from for my fuel pressure experiments had a huge alternator so that voltage didn't swing at all.
but yea, in the end, you put together voltage drops, small pumps that drop pressure at higher rpm, probably too small of piping, and you end up with a VERY nonlinear IFR, almost impossible to predict. at that point you either start replaceing all the bottlenecks or just measure the actual fuel pressure and just adjust for it.

 

Thanks alot for the info guys, i've got to get it retuned soon for more boost anyway. I may even be building a new motor for it. If i change just the IFR tables do you think i could drive it to the dyno which is a couple hours away without causing any problems or should i change out the injectors there?

 

You're still updating the computer. No way around it ... changes must be made to the tune in some way.

There's no way to change injectors without changing some paramaters in the PCM and not running overly rich. short of adjusting fuel pressure, which will then lessen the atomization and you will still prolly run rich, or be dumping raw fuel.

No way ... something has to be changed.