injector duty cycles too high?

[kazzam]

i am tuning my car these days at 17psi on my 50trim. i got fmic, 255lph rewired walbro, 3 inch tbe, ngk7 plugs w/taylor wires. I am on stock 450s and tuning and logging with ECUplus. It tells me everything i need to know. ecuplus.com.
my question is, whats the most injector duty cycle can i run? I have hit 94% or so and experienced sputtering when it gets that high. I have read somwhere that running over 90% idc is a no no--that they starts acting irratic. would that cause my sputtering?
There are no major boost leaks in my system.
I also got 680s in the mail, but would like an answer to my question.
BOost on

 

[Quasimondo]

You shouldn't be running your injectors past 85%. Additionally, you should have an AFPR if you're using a walbro 255. Your tuning is going to be inconsistent with that stock fpr being overrun like that, even with the 680's you plan on installing.

 

[kazzam]

You shouldn't be running your injectors past 85%. Additionally, you should have an AFPR if you're using a walbro 255. Your tuning is going to be inconsistent with that stock fpr being overrun like that, even with the 680's you plan on installing.

i think i know what u are talking about. my runs have been kinda crazy when i try tunning around 17psi or so. however, they been consistent at 15psi and less. at those presures, my injector duty cycles were at 85% max, the car also didn't sputter like when i run 17psi.
I was under the impression that when overrunning the stock fpr, i would be running rich but still consistent fuel delivery. is this not the case?

 

[huafist]

i think i know what u are talking about. my runs have been kinda crazy when i try tunning around 17psi or so. however, they been consistent at 15psi and less. at those presures, my injector duty cycles were at 85% max, the car also didn't sputter like when i run 17psi.
I was under the impression that when overrunning the stock fpr, i would be running rich but still consistent fuel delivery. is this not the case?

Fuel pressure will fluctuate when the FPR is being overran. You're best served getting an AFPR to steady it out.

 

[Quasimondo]

No. The way the fpr works is there is a diaphragm that closes up to restrict the amount of fuel that is returned to the tank. The more it's opened up, the lower the pressure and vice versa. When a fuel pump is too much for the fpr it cannot effectively lower the pressure, and when it's supposed to raise it, it's not doing that at the proper 1:1 ratio. At best, running too much fuel through those injectors will give you poor fuel economy, fouled plugs, and an inconsistent tune. At worst, the the extra fuel you're dumping in there could wash past the rings and contaminate your engine oil and damage your fuel injectors.

 

[kazzam]

well then. i definately need a afpr. a nice shiny one. Red perhaps or blue, to match my spark plug wires. thx for the info.

 

[kelvinb]

WTF how are you getting 17psi on a 50 trim yet im getting over 100% on my 14b at 10psi

 

[chicagoavenger]

WTF how are you getting 17psi on a 50 trim yet im getting over 100% on my 14b at 10psi

Have you pulled and cleaned them? Could be clogged

 

[kazzam]

WTF how are you getting 17psi on a 50 trim yet im getting over 100% on my 14b at 10psi

maybe pump going dead? perhaps boost guage broken? Maybe you running too rich? i was at 70%duty on my 450s at 13psi.
Could be many reasons...

 

[98eclipseRS]

maybe pump going dead? perhaps boost guage broken? Maybe you running too rich? i was at 70%duty on my 450s at 13psi.
Could be many reasons...

Exactly make sure you fuel pump is not about to die, check for boost leaks, run some fuel injector cleaner through the tank as well just to make sure. When the fuel pump can't supply enough fuel to the injectors they stay open for as long as they can to try and scavenge any fuel that is being put into the rail. I had the same problem with my 1000cc's. I ran out of fuel with the 190 so I was seeing 100% duty cycle on them at super low power levels. I have since switched to a 255hp and am seeing 65% duty cycle with more power.

 

[kelvinb]

i just got a brand new 255 and is suppling sufficent fuel according to my afpr....

 

[dnhieu]

how do you check to see if the fuel pump is dead or not?