Injector pulse width & duty cycle

[etmotorsports]

Stupid question is there a limit on the GEN III that limit the injector duty cycle to 80% or pulse width?

[swingtan]

No "hard limit" in the tune as such. It's a limit imposed by the actual flow rate of the injector and the engine RPM. If the engine is turning fast enough that the injector cannot supply enough fuel, then you have hit the 100% IDC limit and the mixtures will lean out past that point. The 80% figure is considered the "safe maximum" to allow for things like transients and a safety margin.

Simon

[5.7ute]

No "hard limit" in the tune as such. It's a limit imposed by the actual flow rate of the injector and the engine RPM. If the engine is turning fast enough that the injector cannot supply enough fuel, then you have hit the 100% IDC limit and the mixtures will lean out past that point. The 80% figure is considered the "safe maximum" to allow for things like transients and a safety margin.

Simon
X2.
FWIW, if there was a hard limit for IBPW it would be 996ms.:shock: I would not like to think what the IDC would be up there lol.

[etmotorsports]

I am seeing 81% duty cycle and i cannot get any more fuel it seems a/f goes lean at the end of the run but duty cycle doesn't go up, i am using the stock operating system keep adding fuel via the MAF but no significant increases, does the VE table still control the fuel even if the you are up in the RPM range and above the throtle position for the MAF to take over?

[mr.prick]

This depends on how the tune is set up.
{B0120} determines when the MAF table is in control.
SD will have the MAF removed, provided the MAF was failed properly.

Make sure your WBO2 is functioning properly. ;)
I've had bad sensors show no change in WOT AFR even after adding fuel.
If adding fuel shows no change to WBO2 readings this maybe the case.

[joecar]

Post log files.

[swingtan]

X2 on the logs, also a copy of the tune would be good....

You can think of IDC as the percentage of time the injector is open, compared to the time it takes for 2 engine revolutions ( or the time from when the inlet valve starts to open, until the next time it starts to open). This second "time" is the maximum amount of time the injector has to supply fuel for a single induction cycle. If the injector is on for the whole of this time, then IDC=100% and you have lost control of fueling.

If you are having issues with IDC, then the exhaust AFR would follow the gm/Cyl trace on a chart. As total airflow increased, AFR's would lean out and then should richen up as the airflow drops after peak torque.

Simon

[etmotorsports]

Checked the fuel pressure its dropping from 62 to 42 at the end of the run...but the pulse width and duty cycle are not climbing.

[joecar]

Checked the fuel pressure its dropping from 62 to 42 at the end of the run...but the pulse width and duty cycle are not climbing.The pressure drop is causing reduced flowrate, and that is the reason why it goes lean.

[swingtan]

Yep, that will be it. Time to check filter, regulator and pump......

[5.7ute]

No matter what the fuel pressure is doing, a raise in VE and or maf should increase IBPW(Then IDC will follow)
A log with maf airflow etc and a tune file would help. (Before & after the increase in airmass)

[swingtan]

Just had a thought.... Any chance this vehicle uses "dual speed pump mode" ? As the Aus guys would know, certain Holden vehicles had an issue with the PCM dropping power to the pump at WOT which would give this problem.

RE: adjusting the VE / MAF..... Yes, raising the values should see a rise in IDC, but if the fuel pressure dropped further ( due to less back pressure from the injectors being open longer ) then final AFR may not move too much.

BTW, 5.7, did you actually pick up 50hp just by going to the 3" and retuning?

[5.7ute]

BTW, 5.7, did you actually pick up 50hp just by going to the 3" and retuning?

Yep, around 50rwhp.
There was an issue with the intermediate pipes between the cat & tailpipe where the exhaust guy used press bends on the original 2 1/2 system. When I upgraded to 3" I had this section remade with mandrel bends here at work. FWIW there was around a 20rwhp increase over no pipes, but I will have to wait to I go down south at xmas again to confirm. Both dyno's I have access to give similar results within 2 rwkw (one a DD the other a mainline)

[etmotorsports]

Well sorry i left out a few important details guys, its an 02 zo6 with exhaust and a procharger D1 at 10 PSI, stock fuel systems, many people told me the system would be enough, i had my doubts. I did think like you 5.7 no matter what the fuel pressure the pulse width should go up, i only had the ve at 120 but also increasing the maf would get more fuel but it only went up by 1 millisecond. I tune ford and dodges quite a bit, only due a few corvettes a year so i am not familiar with how fast the injectors can pulse like older fords will go too almost 33 ms, where new ones only about 29-31 and dodges will go up too 32-33. So when this car didn't seem to increase from 15.5ms to 17.2 with adjustments to the maf i thought that was odd. Another this is the 12000 hz get hit quickly with a ford it would fail the meter and cause a problem.

I know that i should use a custom operating system but i am unsure how it will react with the car, if anything might go away like the Heads up display or anything like that.

here is a log file9279

[5.7ute]

Looks to me like you are pegging the maf. Easy test would be to scale the maf, Ve & IFR & timing tables & do another pull.
I have come across a N/A car with a stuffed fuel pump that I could still get to commanded AFR with 39psi ( WOT fuel pressure). In your case it appears that the lack of fuel pressure has caused you to inflate the airmass tables too high causing the limit to be hit.

[etmotorsports]

Yes that could have been it, raising the maf too much. When you say scale the maf i don't see any tables to rescale or i am missing them?

[5.7ute]

There is no actual scaling tables. What you would do is drop B0101,B5001 & B4001 by the same percentage. Basically telling the pcm that there is less air & the fuel injector flows less so that the injector is still opened for the right amount of time. Timing needs to be modified as the pcm will show less air & you would now have too much timing from the discrepency.
I have to go quickly but will be back in 1/2 hr if you have any more questions.

[5.7ute]

Just to add to the last post. If this is an auto there are some trans tables that will need modifying as well since airflow is used in the torque calculations. Hopefully someone familiar with auto tuning could add to this.

[Sid447]

Checked the fuel pressure its dropping from 62 to 42 at the end of the run...but the pulse width and duty cycle are not climbing.

Had the same thing here recently and it turned out to be a dying pump.
Though even serviceable stock pumps can't maintain nominal pressure at constant high load/rpm (one guy here was running a modified LS7 in a VE SS and ran it at 260+ kph for a stretch and in spite of it being SD & OL it broke through lack of fuel. :doh2:

[etmotorsports]

Installed 255 pump and wiring kit, fuel pressure is good now, pulse width is still only going to 15.5-16 and running lean at 5800 and up too 6200, have raised the maf to its limit, raised the map ve to 139 or so which should be more than enough, and raised PE to 11:1 or so, since the maf is hitting 13411 hz which is just below failing, it will not increase the pulse width, there must be a table i am missing that is responsible for fueling? On a good side the car made 627 RWHP with better air today that last week, what a difference 20 air temp makes and holding the fuel pressure too, up until the limit was hit it made more power above 5500 the more fuel was added. I even tried another 02 sensor on the dyno to make sure it wasn't that they are within .1 of each other.

[swingtan]

As I mentioned before, once you max out the MAF tables for either Frequency or gm/Sec, you loose all metering control for fuel. The PCM will stick to the maximum limit for air flow, even though you may actually be getting way more. In this condition, IDC/IPW will remain static and exhaust AFR's will lean out. My choice would be to go full SD and dump the MAP. It fixes both the frequency and gm/Sec limit.

Simon.

[etmotorsports]

That is what i thought would have to be done. I have a 2 bar map for it but i couldn't get it to calibrate correctly, it would idle for a bit then over fuel at idle. I might not have the right map sensor.

[swingtan]

What did the log show when this happened?

[etmotorsports]

here is the log9370

[swingtan]

That's the tune....... :p

[etmotorsports]

maybe this will work9376

[etmotorsports]

Well the custom os and a 2 bar sensor fixed all the issues. a/f of 11.2:1 all the way to 6200 RPM's great, that custom os is easy to tune just like a dfi system but the wideband isn't built into the data log. I know you can wire it into the log though. I had to turn off the stft and ltft they seemed to be very far off of each other. They didn't jive at all with what the o2 sensor was saying. Not a problem though just used the o2 on the dyno.