Scanned my truck tonight and it shows 92% injector duty cycle at 5600 rpm WOT. Is that normal for the new engines? I was under the impression that over 80% was bad.
Scanned my truck tonight and it shows 92% injector duty cycle at 5600 rpm WOT. Is that normal for the new engines? I was under the impression that over 80% was bad.
2017 Chevy SS Whipple
with air cold enough the airmass is going to increase significantly. if you keep getting >90% all the time then it's time to worry, if it's one just a once in a while sort of thing, then it's just a normal swing
Also duty cycle is strongly dependant on what AFR you are at (verified by a wideband in the exhaust). If your stock vehicle is entering COT and commanding 11.7, then I can easily see that. But if you have no cats and disabled COT, while targeting an AFR of 12.8, then there is something wrong. Good luck!
IATs were in the mid 70s...
I haven't installed the wideband in the truck yet. I will post a log.
2017 Chevy SS Whipple
Don't trust the IDC readings, just use them as an indicator and not a measure.
HPT seems to show 130% or more IDC in some situations and all I can think is that is plain out impossible. There is no way to turn on an injector more that 100% on.
True on over 100%, but that indicates the injectors are too small for what the computer is asking. So bad program or you need bigger injectors.Originally Posted by BBA
what will it harm if i see 95% or more on duty cycle at the top of the shift ,that equates to .1sec at each wot run, I have seen this for at least two years now. Will my Injectors finally just fail?
2020 Jeep Trackhawk, Functional Demon Ram Air Hood, AFE CAI, SW Headers, SW Cats, Solo Cat back Exhaust.
No, I've seen over 117% IDC on stock 2004 GTP, after tuning the AFR to 11.5, the IDC went down to 104%. A 2007 Escalade was at 92% IDC @ 11.0 AFR. After tuning the AFR to 13.0, the IDC went down to 81%. My 2001 Z06 hits 94% IDC with the stock injectors, and I'm planning on a larger cam to improve on the 434 RWHP.
Russ Kemp
It would be intesting to hear from someone who has seen 100% plus IDCs that has also logged with a wideband.
What happened to the AFR at the limit?
IOW, if the injectors went static, the AFR should head lean under those conditions. That would confirm whether or not the high IDC readings are accurate or false.
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Good engineering is simply finding the right wrench to pound in the correct screw.
Once you exceed 100% duty cycle the AFR goes lean. What you will see in a tune when this happens is the VE or MAF table takes a dive at that point. This is usually an effort to keep the AFR at the desired ratio (not good practice). The injectors can not flow more then 100% duty cycle, that is always open throughout the entire crankshaft rotation. What the IDC is as seen in the scanner, is the requested pulse width the ECM has calculated it needs, at that given rpm, to supply the adequate amount of fuel for the given (VE or MAF) airflow amount. Also realize that IDC is directly related to AFR, RPM and pulse width. So if you have an IDC of 95% at 6000 rpms and the AFR is 12.0:1, you can give yourself more room by commanding a leaner AFR, say 13.0:1 and the duty cycle (at 6000 rpms) will drop to 90% (simplified for this discussion). I have been able to take stock 28# injectors to support 450 rwhp at 6500 rpms (IDC of 95%) by commanding a leaner AFR (13.3:1). I only do this with race setups (think NHRA stock eliminator style) or radical setups that have no future mod plans. For daily drivers, I will keep the IDC between 75%-85%, beyond that I request bigger injectors if the IDC is higher or smaller injectors if the IDC is less then my range. Hoep this helps!
Last edited by 12secSS; 12-17-2007 at 07:23 PM.
I think you guys should start posting injector pulse width #s and RPM. Then do the 'duty cycle math' which is easy to sort out.
Too much time is spent on this, with no thought about how long the intake valve is open.
How long the intake valve is open? Who cares! Look up the 'old' bank fire injector systems. (Or TBI) They fire when the valves are open, closed, and otherwise.I think you guys should start posting injector pulse width #s and RPM. Then do the 'duty cycle math' which is easy to sort out.
Too much time is spent on this, with no thought about how long the intake valve is open.
You need load or airflow figured into your RPM's and pulse width to make sense of the posting. You can have 6500 RPM in neutral or full load: what do you think will have the higher pulse width?
The ONLY reason we have multiport independent injectors is so OBDII can shut down one misfiring cylinder for emissions. (Now add DOD to this.)
That does ask the question: if the "92% injector duty cycle at 5600 rpm WOT" put on a trailer would he hit 100% duty cycle or more?
That's right...and excess fuel is there for the next intake opening event...GM compensates for it, even in the newer code. If you've got IDC of 'reported' values of 80% at batch fire (8 fueling events), vs reported 80% SFI (1 fueling event) depending on reported pulse width, you'll end up with calculated duty cycles which really don't correspond to anything unless you know what state (batch or SFI) injection is occuring. We haven't even gotten into intake valve fuel deposits, intake port wetting, and other variables that affect fueling prior to the intake valve opening. I would think that accurate measurement after point of injection would be paramount.
Unedited, no--you typically wouldn't have 6500 in neutral.You need load or airflow figured into your RPM's and pulse width to make sense of the posting. You can have 6500 RPM in neutral or full load: what do you think will have the higher pulse width?
I'm hoping you mean 'unloaded' and 'loaded'.
Well, not the only reason. And it's for catalyst protection, which could result in an emission issue, but not directly as an emissions concern.The ONLY reason we have multiport independent injectors is so OBDII can shut down one misfiring cylinder for emissions. (Now add DOD to this.)
SFI was for better fuel control, individual cylinder fuel trims (which we had back in the early 90's), torque management, abuse modes, cylinder protection, ETC control, and a few others. DOD will probably never work (properly) till the valvetrain co-incides with injector disable. Frontal area on a pickup is just too large at this point to allow DOD to work effectively.
Hopefully he's not towing at 5600 RPM for any sustained time period, but I'd seriously doubt there's a problem. It's because there's an unknown here--what's the actual pulse width vs RPM. This will determine "duty cycle"...you can't tune anything or determine part upgrades properly by monitoring "duty cycle" alone. You can see in this thread that others have seen higher than 100%--a pretty good indicator that it's not something to rely on.That does ask the question: if the "92% injector duty cycle at 5600 rpm WOT" put on a trailer would he hit 100% duty cycle or more?
I'd really hope he's going to use a 4/5gas or at very least an air fuel ratio meter to determine things by.
This is a good read!
http://www.stealth316.com/2-calc-idc.htm
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Stock pump and injectors are designed to work together. If an injector or two stays open the pump should be able to keep up.
If stock pump and bigger injectors are going above 95% or so you could drain fuel pressure and the last injector in stream might be starved and run that piston lean.
The 100% idc is just for reference. Got to looks at the whole package and make sure they compliment each other.
Norm
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