DaveX

I have a 99 Z28 that only has an airlid and a muffler for engine mods. I just got EFI Live, and my injectors are already hitting 80% duty cycle @ 5600 rpm. Is this normal? I was hoping I could do heads/cam and then upgrade if needed. But I guess not. What size injectors do the 99's have from the factory?

Psychopjv

iTrader: (16)

26.6 on the 99's. the smallest of the small.

98turbls1

iTrader: (17)

You may see where you voltage is for your fuel pump...Could be falling off possibly...

moeZ28

iTrader: (7)

80%....correct me if I am wrong, but wouldnt it take quite a bit to max those out from there. I have 28 lb stock injectors in my car, with the mods in my sig, and i am only at 96% duty cycle at peak power. I am upgrading just to be safe, but this was in cold air, like 40* outside today, but I still want to be sure its safe, but I wouldnt think a decent sized cam and some good heads would completely max him out. I may be wrong though. But I would 20% would be alot left in there to play with....

DaveX

Everything I've read says the industry standard for max is 80%. I'm sure you can go over that a little, but if your running at 96% I think your running the risk of going lean at high rpm.

Where do I find that, and what is considered the upper limit?


Thanks for the replies everyone.

MeentSS02

iTrader: (11)

You are dropping fuel pressure...it isn't being caused by voltage (at least not that I can tell)...it is just how our stock fuel systems work. My 28.8 lb stock injectors were at 90-95% duty cycle with just bolt-ons...looking at the fuel pressure at WOT told me why. In the upper RPMs, the pressure drops to 51-52 psi (instead of the 58 it is at idle).

warp_6

iTrader: (2)

What's your WOT a/f ratio? With full bolt-ons and my WOT table still stk (some where in the 11's) my injector duty cycle was in the 80% range. Just adjusting my WOT table to 13.1- 12.9 (n/a car) dropped my duty cycle down in the 60% range. Fuel pressure was always steady.
I have since upgraded the pump for future mods. H/C parts are arriving daily. I might have to upgrade the injectors after the install.

DaveX

I don't know, I don't have my wideband installed yet and I'm still finding my way around the software and logging/tuning. I haven't changed anything that would affect the a/f ratio as tuned from the factory though.

MeentSS02

iTrader: (11)

If it is the factory tune, then you are around 11.5-12:1 AF ratio at WOT...your duty cycle will decrease once you lean it out (with your wideband for verification, of course).