What is Too Low of a Duty Cycle for Injectors?
02-15-2017, 02:57 PM
#1
Safety Car
Thread Starter
What is Too Low of a Duty Cycle for Injectors?
Long story short: I built engine for forced induction, bought injectors for lots of hp and decided later to go back naturally aspirated. Just starting to tune this thing and notice at idle the duty cycle on the injectors is really low. I can't remember the exact numbers right now, but will post tonight when I get to the data log. How low is too low that it will adversely affect driveability? I know I probably need more like 40 lb injectors and I have 60s.
Last edited by LTxDave; 02-15-2017 at 02:58 PM.
02-15-2017, 04:09 PM
#2
Melting Slicks
Member Since: Jan 2014
Location: Downers Grove Illinois
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It depends on the injector. You need to find a flow versus pulse width graph and make sure it is in the linear portion of the graph at idle for best idle characteristics.
02-15-2017, 10:59 PM
#3
Safety Car
Thread Starter
The minimum is 1.5% at idle. I have an Excel file with the characteristics of my siemens 60 lb injectors, but I don't see the info you referenced.
02-16-2017, 09:21 AM
#5
Safety Car
Thread Starter
Yeah, I know how to create a graph in Excel. There's no data labeled flow and pulse width. There is a minimum pw listed and flow for different pressures and different voltage.
02-16-2017, 09:33 AM
#6
Melting Slicks
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Got it, do you have the injector part number? What is the minimum pulse width listed? What is your idle speed target?
Last edited by JimLentz; 02-16-2017 at 09:37 AM.
02-18-2017, 05:24 AM
#7
Melting Slicks
Example: (8) 63 lb injectors idling at 700 rpm in double fire mode (350 @ 900 ft elevation, 50 psi fuel pressure, E10):
Last edited by tequilaboy; 02-18-2017 at 05:34 AM.
02-18-2017, 05:30 AM
#8
Melting Slicks
So if you have integrator activity and O2 sensor activity, you can run lean enough on a given injector. Can't go much below ~900 ms for min pw on these injectors or they won't open reliably.
If your ecm can idle in single fire mode, there should be no issues. Double fire is worst case. Spinning my blower does add a little load which tends to help. A naturally aspirated 350 in double fire mode would be borderline rich at idle/light load conditions.
You can always reduce fuel pressure or add a little ethanol to the mix if necessary to run lean enough at the min pw.
If your ecm can idle in single fire mode, there should be no issues. Double fire is worst case. Spinning my blower does add a little load which tends to help. A naturally aspirated 350 in double fire mode would be borderline rich at idle/light load conditions.
You can always reduce fuel pressure or add a little ethanol to the mix if necessary to run lean enough at the min pw.
Last edited by tequilaboy; 02-18-2017 at 05:41 AM.
02-18-2017, 05:56 AM
#9
Melting Slicks
Same log: 50 mph road load. similar pw. You can see that the INT is sometimes being clipped as the min pw limit is reached, but resulting mixture is still on the money.
Note: Higher rpm and lighter load situations than my examples can be problematic.
Note: Higher rpm and lighter load situations than my examples can be problematic.
Last edited by tequilaboy; 02-18-2017 at 07:50 AM.
02-18-2017, 08:08 AM
#10
Melting Slicks
Situations like this will always be rich (2500+ rpm, 2nd gear cruise/decel, min pulse width limit in effect, integrator frozen at 128 ). So if you like to buzz around in the lower gears at 3500 rpm, might be an issue.
Again, single fire mode can alleviate most if not all of these issues with big injectors.
Based on your own data, you should be able to decide if they will work for you.
Again, single fire mode can alleviate most if not all of these issues with big injectors.
Based on your own data, you should be able to decide if they will work for you.
02-18-2017, 08:40 AM
#11
Safety Car
Thread Starter
The info I have lists them as Siemens 60# @3 bar or ford racing M-953-LU60. The min pulse width listed is 0.8ms. Idle speed target right now is 1000 rpm, but I would like to lower. At 1000 rpm, coming to a stop it feels like its going to die. I also have a big stumble off idle.
02-18-2017, 08:46 AM
#12
Safety Car
Thread Starter
I'll have to look at the logs tonight when I'm not on my phone. A few comments though: Not sure I can select single or double fire mode with the factory PCM. The engine is a fairly stout 383 with AFR heads. Running E10-15 pump gas, no E85 available in my area.
