Misfire with new fuel pump and injectors
 

Wrx import. On the advice of the scooby clinic. Before a remap. i have Uprated the fuel pump to a Walbro 255 and put in some sti 440cc yellow injectors. But now the car won't run properly and misfires like a bitch when I touch the throttle. Is this because it hasn't had it's new ecu and remap yet or is something not working properly?

Mine ran like a dog after I swapped 380 for 440 injectors. Duncan racedynamix put it right.

Its likely to be the bigger injectors.

Think about it...ECU opens each injector for x number of milliseconds per intake stroke. for each millisecond it assumes x number of microliters of fuel is injected. It also increases the injection duration under load/acelaration.

With a bigger cc injector, you've increased the amount of fuel injected per millisecond. The ECU won't magically know this without either a)adaptive values being reset and the mixture being within the adaption limits when in closed loop running (which it won't be when its cold as the engine has to be warm to run in full closed loop mode) and b) reprograming the ECU so it knows not to open the injectors for so long (remap).

Not sure why you'd be advised to fit bigger injectors without being warned you that it'll upset the fuel mixture/running.


Of course I'm assuming your new fuel pump isn't aerating the fuel from poor pipe fittings and the fuel pressure is correct. Easily checked with a guage and flow test into a container.