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Injector duty Cycle

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Old 01-13-2018, 02:11 PM
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Injector duty Cycle

Anyone ever check the injector pulse width at full boost. At 14lbs with headers and tune I see 30% at 6k rpm. This is a very low number for stock injectors I would think. Anyone ever log there stockers on a modded motor?

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Old 01-13-2018, 03:39 PM
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You think that's LOW???
Given that there's only one injection event per 4 strokes of a piston, I'd call 30% high. What am I missing here?
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Old 01-13-2018, 04:31 PM
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Dang !! I was thinking overall and I think you are correct.
The reason I am asking is because I never tested duty cycle until now.
What happened was I just installed some 550cc injectors {Bosh with pigtails} and they will not run under boost...stutters,hesitates,runs extremely lean {pegs wide band} and overall like crap but only under any kind of boost ...almost like random miss fires as well. So put back the original injectors,loaded the tune in and all is well. So I thought ok I wonder where these injectors are at duty cycle wise ...maybe stock injectors are fine. So logged Duty cycle and they are at around 30% which is way to high.
Now I have to figure out why the 550cc injectors run so poorly.
Original injectors ohm out at 11ohms and the 550's with the pig tail are at 15 ohms. Don't know if that matters.

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Old 01-13-2018, 05:44 PM
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I would call it low. Certainly you don't want to get anywhere near static but as an OEM manufacturer you will have the best idle and driveability using the smallest injector you can while still allowing a decent safety net. I am sure many cars in the past have had duty cycle in the 70-90 range. My old Toyotas with the 3SGTE engine certainly had very little overhead with mods before hitting 100%.
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Old 01-13-2018, 06:06 PM
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Well after the calculations overall its at 130% Duty which means they are going static real early. Not good.
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Old 01-13-2018, 08:28 PM
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Originally Posted by SICAMG View Post
Well after the calculations overall its at 130% Duty which means they are going static real early. Not good.
That isn't plausible otherwise you would be running very lean if you require 1.3x the maximum fuel your injectors could supply. Your engine would be destroyed.
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Old 01-13-2018, 09:55 PM
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Plausible...no. But it's only the math that's showing it is way over 100% according to on line injector calculators. Still not to sure of this.
http://www.gtsparkplugs.com/Injector_Duty_Cycle.html

http://injector-rehab.com/shop/idc.html

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Old 01-13-2018, 10:28 PM
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Where are you getting the pulse width data from to use in that calculator?
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Old 01-13-2018, 11:17 PM
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I am trying to calculate this correctly. My gauge will say 30%. Now that's only recording one injector and that's all we need. Rpm is factored in ?????
There is no way that is all the duty cycle being used ...even stock if the engine makes 500hp on 39lb injectors it would have to be higher...no ?

Now I am going in circles here LOL !!!

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Old 01-14-2018, 12:38 PM
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Originally Posted by SICAMG View Post
I am trying to calculate this correctly. My gauge will say 30%. Now that's only recording one injector and that's all we need. Rpm is factored in ?????
There is no way that is all the duty cycle being used ...even stock if the engine makes 500hp on 39lb injectors it would have to be higher...no ?

Now I am going in circles here LOL !!!
Also have to make sure your putting in our 80 psi pressure most use 43.5 psi ours runs super high pressure .... I like this site to do my calcs https://fuelinjectorclinic.com/flow-calculator and according to this site to get 550 wheel HP with 85% duty cycle and 80 psi it needs a 38 lb injector.


Also how are you monitoring duty cycle is it with torque pro or dash command I ahve both but cant seem to find that parameter to monitor

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Old 01-14-2018, 12:49 PM
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You should probably monitor your fuel pressure also when doing this test
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Old 01-14-2018, 01:31 PM
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Well my gauge is recording Injector Pulse Width so that has to be changed over to duty cycle ?????? Just ran the car again and it shows 27%-28% Pulse Width on injector one. So what the hell is that come out to in Duty Cycle !! ??
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Old 01-14-2018, 02:41 PM
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Pulse width is measured in ms at a certain psi as mentioned above, not a %.
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Old 01-14-2018, 03:07 PM
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Originally Posted by tw2 View Post
Pulse width is measured in ms at a certain psi as mentioned above, not a %.
x2

If it is giving you a percent it is injector duty cycle. You are good man

Injector duty cycle is taking pulse width and rpms to determine how long the injector is actually open over the maximum period(based on RPM) that they could be commanded open. All calculations are being done for you already.

The online calculators you are looking at are for something reading out an actual frequency of the injector signal, then doing the math based on RPMs to determine pulse width, then deviding the pulse width by maximum potential injector period and giving you a duty cycle. Punching a duty cycle or pulse width reading into one of those calculators is just going to give you garbage, it's basically redoing the calculation that your meter has already done

EDIT: Found this, they explain it much better than me haha: http://www.ecmtuning.com/wiki/injector-duty-cycle
But basically, your gauge reading out in percentage is not 100% means that they are just always open, its based off the maximum potential period of pulse width for the firing cycle. 30% means you have tons of fuel left.

Last edited by drothgeb; 01-14-2018 at 03:13 PM.
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Old 01-14-2018, 07:25 PM
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A reading of 30 seems very low for a modded engine with more boost. I would think I would be in the 60 range but who knows.
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Old 01-14-2018, 08:25 PM
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Originally Posted by SICAMG View Post
A reading of 30 seems very low for a modded engine with more boost. I would think I would be in the 60 range but who knows.
I kind of agree 30% seems low especially if people are having to move up in injector size with just a little more boost. What are your AFRs?

What meter are you using to log your duty cycle?
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Old 01-14-2018, 08:49 PM
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Originally Posted by SICAMG View Post
A reading of 30 seems very low for a modded engine with more boost. I would think I would be in the 60 range but who knows.
Yes your number is not real. Not to be a dick but whatever you are reading or doing is wrong.
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Old 01-15-2018, 04:20 PM
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Aeroforce scan gauge

Injector Pulse width 1----bank 1
Injector Pulse width 2 ----bank 2
Around 2-3 at idle and 28-30 at full boost. Don't have any solid info on what the numbers mean with the gauge.The company has no tech line to call.

This is all that is seen on the gauge. I would assume something is not correct but this is all the information I have.
I will hook up stars and see as well to compare numbers
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Old 01-15-2018, 05:08 PM
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Does this connect through the OBD2 port or hardwired in? It is a bit difficult without knowing what the gauge is measuring. It could well be the pulse width in milliseconds. I don't know exactly how these ECUs control the injection frequency.
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Old 01-15-2018, 05:16 PM
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Originally Posted by tw2 View Post
Does this connect through the OBD2 port or hardwired in? It is a bit difficult without knowing what the gauge is measuring. It could well be the pulse width in milliseconds. I don't know exactly how these ECUs control the injection frequency.
Those gauges are OBDII readers. I would almost venture to guess that maybe they don't have the MB ECU as figured out as they had hoped? I have used one before and liked it but it was on a Dodge. It seems MB goes out of there way to keep their proprietary ECU stuff a secret.

I almost bought one again for the Benz because I wanted knock retard.... This has me skeptical though :-(
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Old 01-15-2018, 07:56 PM
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Just checked DAS and it show's the same thing. Injector Time MS left and Injector Time Right. You can not pick one single injector by the looks of it.
So the gauge is correct in what it reads ..Left and Right side 30ms. Now weather that's averaging out all 4 injectors,I do not know.
.

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Old 01-15-2018, 08:44 PM
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Originally Posted by SICAMG View Post
Just checked DAS and it show's the same thing. Injector Time MS left and Injector Time Right. You can not pick one single injector by the looks of it.
So the gauge is correct in what it reads ..Left and Right side 30ms. Now weather that's averaging out all 4 injectors,I do not know.
.

30ms is your pulse width then, so you were right then with your 150% duty cycle.

Do you have a wideband? I would not go WOT without seeing where your AFR is.
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Old 01-15-2018, 09:01 PM
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It's right around 11.2 all the time under boost so its good. I have two wide bands...one is a fail safe set up for the supercharger so no worry's there.
I am waiting for a response from my tuner to figure out why the 550 injectors will not run correctly then I should be ok injector wise.
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Old 01-15-2018, 09:09 PM
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If you are at 11.2 AFR then you are not a at 150% (theoretical) duty cycle otherwise you would be running static open injectors and still only get 2/3 of the fuel delivery your ECU is asking for. Do you actually have a driveability problem or is it just based on this data that you are concerned?
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Old 01-15-2018, 09:36 PM
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Originally Posted by tw2 View Post
If you are at 11.2 AFR then you are not a at 150% (theoretical) duty cycle otherwise you would be running static open injectors and still only get 2/3 of the fuel delivery your ECU is asking for. Do you actually have a driveability problem or is it just based on this data that you are concerned?

agreed his afr wouldnt be so stable if he was hitting over 100% idc .... that would mean its static an cant be controlled so well. Something else is amiss whether the calulations or other factor its not right
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