>95% Injector Duty Cycle?

[5_Liter_Eater]

While logging my dyno runs to dial in my AFR I noticed that the duty cycle % was damn near 100%! I thought 42#ers were plenty big for ~500 HP. I had some bad valve float at ~5500 so I wasn't able to get the top end AFR dialed in entirely but it's between 10:1-12:1. Could it just be that my PE is too high or something?

[WS6FirebirdTA00]

if the afr is too high it will cause high duty cycle. a boosted application will need more fuel. i think 500 rwhp on 42#ers @ 80% is for n/a cars.

[Bill@HPTuners]

if the afr is too high it will cause high duty cycle. a boosted application will need more fuel. i think 500 rwhp on 42#ers @ 80% is for n/a cars.

werd...those very well might be undersized for your application

[S2H]

42's are a little light for FI....
I think FI guys are going up into the 52-60 range on injector size....
also remember if you have an SVO injector you get a little more than what its rated at because SVO are usually rated at 40psi instead of the 58 we have

[WS6FirebirdTA00]

yeah they are actually like 48#'s or so

[Bill@HPTuners]

so many things here
1. log commanded afr
2. log timing advance
3. why is bank 2 sensor 1 dead?
4. I would say you'll probably be over 100% duty cycle at that mph on the street/track and probably over 100% on lower gears as well.

[5_Liter_Eater]

Commanded AFR would just be stoich divided by PE right? My PE ramps up from 1.145 @ 4000 to 1.3 @ 6000. I didn't log advance because I ran out of PIDs and I knew what my advance was (13 degrees). Sensor 2 is dead because we yanked it to put the wide band O2 from the dyno into it's bung.

I can't believe I'm runing out of injector! I thought I'd need to be ~600 RWHP to need 60#ers. Now that I look at the injector worksheet on RC Engineering though I guess it's true. 42#ers (rated at 43.5 like my green tops are) hit 80% duty cycle at 565 BHP with a BSFC of .55.

[WS6FirebirdTA00]

u want to put the WB in the driver side header, the driver side will run the leanest. you need to redo the ve table i think so the pe doesnt change so drasticly.

[Bill@HPTuners]

you do realize you will go into open loop when you take out that front o2 right? Your trims are 0'd out which means you couldve deleted those & put in 4 more pids in their place dont ya think? And for that matter cant you log 48bytes now with 2.0?

[5_Liter_Eater]

And for that matter cant you log 48bytes now with 2.0?

Drrr...You're right. Don't know why I was limiting myself to 24.

[Main_One]

I've got a friend who I'm seeing duty cycle readings of up to 113%. How can it go above 100%? He's got a supercharger on his 5.3 truck engine, and a device which ups his fuel pressure to 100#s when the supercharger is hitting hard. The duty cycle readings cross 100% at about 5000 rpm. He's thinking about wideband O2 sensors, but his stock ones are staying above 870 mV from 4000 rpm on up to where he gets a gear shift.

[Russ K]

Your need to check the afr with a wideband, 1000 + mv at wot seems too rich.
1.3 pe = 11.3 afr.

Russ Kemp

[S2H]

narrowbands change from day to day...
1000mv might be jus fine one day and rich another and lean another...

either way..you cant really tell without a wideband

[EC_Tune]

SE,
Gonna disagree slightly with you on the 1000 mv stuff.
Any time I have seen 1000 mv it's definitely been rich. 980 on down is anyone's guess. Only way I could think of to get there would be dead cold o2's, start it up & floor it.

5LiterEater:
If you're above 7lbs boost and fuel pressure is not *at least* 55 PSI under boost you will get those kinds of readings with 42's. You should be near 60 PSI pressure for your app.

EC

[Main_One]

But why am I getting 113% duty cycle for the injectors???

[WS6FirebirdTA00]

But why am I getting 113% duty cycle for the injectors???

If I was your friend I wouldnt be running the car unless he wants to blow it up. What do you mean, by why are you getting 113%? Seems like you are asking more because I woudl think it would stand out. You are hitting 113% because your injectors cannot handle the fueling, they are too small, it shows in the o2 reading which is lean for an NA car.

[Main_One]

Maybe I should have been more specific about where his O2 readings are at. Right at the shift his duty cycles are hitting 115%, and his O2 readings are 907 and 938. Those numbers don't seem too lean to me, but I'm a bit of a newbie at this. After the shift, they drop down to 881 and 898, and the duty cycle is less than 60%.

[WS6FirebirdTA00]

that makes no sense to me, but what you are worried about is what is going on when you are accelerating, and those numbers still look lean based on average mV for a given AFR that I have personally seen. On a supercharged car you should never get into things without a WB, $197 bucks is a lot cheaper than a new motor and also the tuning software...

[RomansDesigns]

100% duty cycle means the injectors are on 100% of the available time. 100+% = STATIC, the injectors are wide open. At this point you are hoping the FMU is giving enough pressure that you aren't leaning out, but the ecm has lost all control. I had this on a 5.3 with a Vortech and FMU. We took the FMU off, istalled a set of SVO 42's and I was able to get the WOT AFR's to about 12.2 to 1 and not hit over 80% duty cycle. (We had to install a bigger fuel pump too)
Mark

[SRPerformance]

100% duty cycle means the injector is open for one complete revolution of the crankshaft, hence you can go over but the recommendation is 80% max.

Power wise once you hit 100% you wont lose power but if you fit larger injectors you will make more peak power.

Joe