Injector duty cycle in relation to fuel pump...

[VtecvrsTurbo]

So im a little bit confused on this. From what ive read, injector duty is amount of time durning cycle. So a weak fuel pump (unwired 2g stock pump) can cause the injector duty cycle to rise considering the flow isnt there? Im wondering why a few years ago on my stock GST, i got a dyno done and my IDC was almost 100% with a T-25 at 15psi. But my current car, a 99 GST with a s16g and no fuel mods at the moment can run 10-12 psi safely (according to many other threads on this site). Something just doesnt seem right. Im on wastegate pressure (8 psi) until i figure this out.

 

[LandSpeed-DSM]

So im a little bit confused on this. From what ive read, injector duty is amount of time durning cycle. So a weak fuel pump (unwired 2g stock pump) can cause the injector duty cycle to rise considering the flow isnt there? Im wondering why a few years ago on my stock GST, i got a dyno done and my IDC was almost 100% with a T-25 at 15psi. But my current car, a 99 GST with a s16g and no fuel mods at the moment can run 10-12 psi safely (according to many other threads on this site). Something just doesnt seem right. Im on wastegate pressure (8 psi) until i figure this out.

That part in bold is correct, yes. An astonishingly small number of people seem to get this.

 

[donniekak]

A weak pump will not cause high idcs on a car running the stock tune. It will just run leaner, as there is no closed loop feedback at wot.

Now, if you're tuning a car, a pump at its limit shows itself easily. You increase the ipw, and nothing happens, it gets no richer you have reached max flow of the pump.

 

[VtecvrsTurbo]

A weak pump will not cause high idcs on a car running the stock tune. It will just run leaner, as there is no closed loop feedback at wot.

Now, if you're tuning a car, a pump at its limit shows itself easily. You increase the ipw, and nothing happens, it gets no richer you have reached max flow of the pump.

So the above statement makes perfect sense to me. Obviously theres no feedback durning closed loop which in turn wouldnt allow the ECU to adjust for leaner conditions. So back to my original question, the unwired pump wouldnt have anything to do with IDC except during open loop conditions?

That part in bold is correct, yes. An astonishingly small number of people seem to get this.

Only in open loop conditions? Because both post responses kinda contradict themselves.

 

[LandSpeed-DSM]

So the above statement makes perfect sense to me. Obviously theres no feedback durning closed loop which in turn wouldnt allow the ECU to adjust for leaner conditions. So back to my original question, the unwired pump wouldnt have anything to do with IDC except during open loop conditions?



Only in open loop conditions? Because both post responses kinda contradict themselves.

They are both correct, and do not contradict each other. I chose my words and those of yours that I bolded carefully.

You do seem confused though..

Open Loop = No sensor feedback.
Closed Loop = Sensor feedback.

These are the criteria for them (See Details):
fueltrimupdatepoints [ECMTuning - wiki]

 

[VtecvrsTurbo]

They are both correct, and do not contradict each other. I chose my words and those of yours that I bolded carefully.

You do seem confused though..

Open Loop = No sensor feedback.
Closed Loop = Sensor feedback.

These are the criteria for them (See Details):
fueltrimupdatepoints [ECMTuning - wiki]

Yea I get all the sensor part, when it reads and when it doesnt. But the part I dont understand is, if a pump has weak flow, how would that cause higher IDC when it is in open loop conditions and it doesn't compensate for less fuel?

I think i got mixed up earlier with open/closed loop, but I knew which was which

cool, well thats what I was looking for I guess, reasons why my other car had such high IDCs at only 15psi with a T-25.

So considering my current car is up do date on MX and well inspected (boost leaks, etc.) I should be fine at the 10-12 psi that everyone seems to think is safe for a 16g on stock fuel? Im just one of the people that research EVERYTHING before doing it

 

[daplatano91]

I'll make it easy for you. If your duty cycle was that high on the stock turbo with stock injectors, fuel pump and not rewired then your duty cycle can still be very high rewired with the 16g. The only way to know is to datalog your car on a pull. No one can give you that information each car will run differently each tune is not the same. Duty cycle will raise or lower based on the air fuel ratio your targeting as well. For instance if your targeting 10.5 your duty cycle will be high than if your targeting 11.5 because the injector needs to flow more to achieve that richer fuel ratio.
So there's too many variables in play for you to just do a search and figure you'll be ok. Leave the car at wastegate pressure make a pull insure your airfuel ratio is where you want it. Then refer to your datalog of that pull to see what your duty cycle is. If the duty cycle is below 85% (this is the percent many people would consider safe) you can possibly raise boost. If the duty cycle is higher look into bigger injectors and possibly a pump that will flow more.

 

[VtecvrsTurbo]

Thanks man, ill take that route. Seems like the smartest and safest bet.

 

[bcowx06]

http://www.dsmtuners.com/forums/articles-tuning-ecu/366003-injector-fuel-pump-supported-airflow.html

 

[DSMReviver]

To put it like this... The injectors have to open more/pulse width increase because the pump is not providing enough pressure. It is over working to support enough fuel(injectors)

 

[steve]

To put it like this... The injectors have to open more/pulse width increase because the pump is not providing enough pressure. It is over working to support enough fuel(injectors)

The point was how are the injectors going to open more?

The ECU controls the injector pulse width (IPW) based on measured airflow, and a few sensors but only knows what the resulting AFR is during closed loop, when it takes feedback from the O2 sensor.

Without feedback there isn't anything to increase the IPW to account for low fuel pressure and cause the IDC's to change. The AFR changes instead.