Injector duty cycle above 100%

[ls1vt209]

Why is it that we can see above 100% duty cycle when scanning (I am currently seeing 128% at 6400rpm) if the injector cannot do more than 100%DC?

I know it's a dumb question but I need an answer.

Cheers

[macca_779]

basically at above 100% its out of the window to which fuel should be injected. So what your seeing is fuel being injected to late on the intake stroke.. On top of that, your deep in to static injection territory and will basically have stuff all to zero fuel control. Moral of the story. Upgrade your injectors.

[ssvolvo]

Mine was showing high also and I knew the inj. were sized properly. I was using the wrong PID. There are 2 PIDS for inj base pulse width. Be sure you use the correct one.

Mine is an LS2 though and may not apply to yours.

One can also verify duty cycle with a decent digital volt ohm meter (DVOM)hooked thru the injector harness.

Good luck, John

[joecar]

100% == injector statically held open for the 2 revolutions of a complete 4 stroke cycle.

> 100% means that the PCM can't provide enough fuel.

You either have a big motor, a big airleak, a big lack of fuel, or the wrong pids.

[ls1vt209]

basically at above 100% its out of the window to which fuel should be injected. So what your seeing is fuel being injected to late on the intake stroke.. On top of that, your deep in to static injection territory and will basically have stuff all to zero fuel control. Moral of the story. Upgrade your injectors.

Have 36lbers in it but I think the fuel pump is the prob half way through an upgrade.


100% == injector statically held open for the 2 revolutions of a complete 4 stroke cycle.

> 100% means that the PCM can't provide enough fuel.

You either have a big motor, a big airleak, a big lack of fuel, or the wrong pids.

No big motor just a blower on stock motor. I thought the 36ers would have been big enough hence why I am changing fuel system.

No air leak. Right pids.


Same thing with my mates car who is running a Vortech blower with standard pulley on a VZ Berlina wagon (Gen 3), he is also running 36lb inj's and is seeing well above 100% duty cycle above 6000rpm.


My original question actually related to the fact that EfiLive will allow us to see above 100%, why not just stop it at 100.

[ssvolvo]

Because base pulse width goes thru the roof once the injectors go static. The ECM can't command any more fuel but keeps trying. Check your base pulse width when full fueling is occuring...pulse width is at 24 milliseconds. 24 Ms X 6400rpm divided by 1200 = 128%
I'm am not much at math, so most any other techie on the forum could put this on paper better than myself. Maybe your question might be better asked: Why does base pulse width keep rising once your fueling is maxed?

I had a similar problem but finally realized my wide band had gone kaflooie! I didn't actually need bigger injectors, I just kept upping my VE table until the engine wouldn't run it was so rich. When I saw those big #s you are talking about I reverse engineered the equation and then understood that the calculation is based on pulse width.

[joecar]

It takes 2 revs to do 1 complete 4 stroke cycle...
(units are shown in square [ ] brackets)

Time taken for 2 revs [ms/cycle]
= 2 [rev/cycle] / (RPM [rev/min] / 60 [s/min]) * 1000 [ms/s]
= 2 [rev/cycle] * 60 [s/min] * 1000 [ms/s] / RPM [rev/min]
= (120,000 / RPM) [ms/cycle]

Injector Duty Cycle [%]
= IBPW [ms] * 100 [%/cycle] / ((120,000 / RPM) [ms/cycle])
= (IBPW * RPM / 1200) [%]

Note how the units cancel out (this is important)

For example, say 6000 rev/min:
Time for 1 rev = 1/(6000 [rev/min] / 60 [s/min]) = 1 / 100 [rev/s] = 0.01 s = 10 ms.
Time for 2 rev = 20 ms <--- this is 100% DC (Duty Cycle) @ 6000 rpm
If IBPW is 10 ms, then this is 50% DC.

For example, say 600 rev/min:
Time for 1 rev = 1/(600 [rev/min] / 60 [s/min]) = 1 / 10 [rev/s] = 0.1 s = 100 ms.
Time for 2 rev = 200 ms <--- this is 100% DC (Duty Cycle) @ 600 rpm
If IBPW is 10 ms, then this is 5% DC.

PCM can compute that 128% is required to spray the fuel mass required to meet a specific AFR based on a computed cylinder airmass, but physically the injectors cannot open any further than 100%... 100% represents maximum static full open.

DC greater than 100% means that for some reason the PCM has computed a large cylinder airmass.

[TAQuickness]

DC greater than 100% means that for some reason the PCM has computed a large cylinder airmass.

Also means that you injectors are being held open, unable to deliver the required fuel, and prematurely wearing out.

Best to use the proper sized injector for the application. Oversizing injectors creates headaches when tuning for small pulse drivability.

[Chuck L.]

FI and you have the FPR boost referenced, right???
If not, then the fp will not rise w/boost and the flow will not keep up w/ the commanded flow...
Have you logged fp when in boost??