OEM injector duty cycle

Megan370z

Ive been doing some tuning since I got the car back (blown transmission)
and I discovered that my injectors were getting up to 85% duty cycle.

isnt it on the high safety side ?
I heard different opinion when the injector goes over 85

any experienced peoples that could shim in ?

alecnet

I realize this is a bit of an old thread but hopefully I can still help. I'm new to VQ engines but I have a bit of experience tuning older Z's and the fundamentals are pretty much the same when it comes to tuning EFI.

Approaching 85% duty cycle is usually a sign that larger injectors are required, especially if you are consistently going over 80% DC. A max of 80% duty cycle has always been the rule of thumb that I've followed when setting up engines. Start going over that (using a solid tune) and you run the risk of your injectors not being able to respond quick enough and behaving as if essentially wide open. This limits your ECM's ability to accurately control what your injectors are doing during the most critical time, WOT and high RPM.

I don't know how modified your car is, but have you made significant mods that would require more fuel than stock? What are your AFRs when duty cycle approaches 85% and when does this occur, i.e. long WOT runs, slamming open throttle, etc?

Megan370z

at 85% my afr at WOT is 12.5-12.8 @ +-15deg C

I did some change that required some tuning a few weeks ago and at -20deg C
I was at 95-98% at 11.5-11.7

Custom; CAI /Throttle body/Intake manifold/step long tube headers/Custom X-pipe & free flow muffler.

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