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If you buy used/reconditioned, they do not replace the electrical actuator (coil) that releases gasoline. But they are cleaned and measured. To me, a used one is prone to failure sooner since it's been in service longer. As I'm in the middle of the replacement project, you don't want to do it more than once!
Avoid 24 lb (or higher) injectors because they are likely to make your car run richer. And, you don't need that size unless you do several HP upgrades. Even 21 lb injectors are good to 300 HP! And, if you look at Vader's website, you'll see a fully modded L98 (heads/cam) pulling good times with original 22lb injectors. You don't need to go bigger.
The ECM will compensate -- by shortening/lengthening the pulse duration for bigger/smaller injectors. IMO, you'd want the same or smaller. I would think they'd atomize fuel better (than a shortened pulse larger injector).
Gregg
Why buy new ones and pay more than twice the price and a 1 year (if that much) warranty with a lot of hassle to replace it. You get a 3 year (no questions asked) warranty from FIC @ www.fuelinjectorconnection.com and you won't find better before and after service than you can get with Jon. Also, new ones don't come in matched sets for flow and electrical properties as do FIC'S.
New coils can fail to, anything electrical can, and if they do, you will have to buy another unmatched injector. FIC's are tested more than once for quality and performance.
If the ECM will compensate for the 24# replacement, then why would the car run richer? You will have to tune the ECM for the 24#'ers to make it run right. The tables have to be corrected for it to properly calculate the right amount of A/F ratio that the engine needs.