Injector Duty

[SDEWY5]

First off, if im hitting roughly 75% duty cycle, making 270kw and running a GT35 at 16psi does 620cc sound kinda right? Theyre std hi-flowed injectors.

And main reason for this post, does the PFC have some sort of overfuel safety thing? when my car is cold i never drive it on boost, only when its up to temp will i give it a squirt. What ive noticed is that when i initially give it a hit once its up to temp the duty cycle seems to spike by about 10-12% (black smoke fromexhaust running rich). Then if i reset the hand controller and give it another hit it will register normally again from then on. The whole car runs immaculately but this odd spiking in duty cycle has got me scratching my head. Anyone know what im on about? (also im not running an o2 sensor at the moment but i didnt think that would have any effect on overfuel)

My boost control is 100% stable, 16psi on the dot all day everyday...

[R31Nismoid]

75% is probably around the mark 620's IMO.

Being 440's will do 300rwkw at around 95-100%

Whats the fuel pressure like? Could be a pump on the way out. Also the tune comes into effect, how much fuel its being told to use and so on so its very much subjective

[Cjmartz2k]

75% is probably around the mark 620's IMO.

Being 440's will do 300rwkw at around 95-100%

Whats the fuel pressure like? Could be a pump on the way out. Also the tune comes into effect, how much fuel its being told to use and so on so its very much subjective

The ECU doesn't sense lower pressure and give more injector to make up for it. I'm not sure if that's what you were meaning though.

OP-Does your air flow voltage spike along with the injector spike? It could be a loose connection to it or an intermittent boost leak. Also, if you have a faulty coolant temp sensor or loose connection to it, the ecu would see a really low temp for a second and push it into "start up" mode for a split second upping your fuel.

[R31Nismoid]

No i meant as in just check in general.

Might have been failing/tired perhaps during/before the tune or something, 75% is about right being its subjective to how the tune is, but to tell a better story without any influence having a look @ the rail pressures will help... it was kinda a side thing.

[Cjmartz2k]

Gotcha. Understand where you're coming from now.

I still say check the CTS and AFM.

[SDEWY5]

interesting, thanks for the feedback guys i will be checking the AFM voltage as that seems it could be a good indicator. The pump is a Walbro...never been that happy with the sound of the pump when it primes itself when ignition is turned to reds, makes an odd rubber on rubber friction noise, hard to describe, best description would be when you sit on a leather couch and hear the cushions rub together...odd i know...replacing with an 044 soon.

JEM tuned the car just before christmas last year, not sure on rail pressure but will now be checking it. I do know the overall tune is pretty conservative for reliability (used to do alot of supersprints and had a fairly long stream of bad luck with engines failing).

[Beer Baron]

yes PFC does have eng temp compensation built it. so if it's been set-up at certain water temps it can enrichen the fuel map. have a look at it in the HC. you can see what it's set to.

[Guilt-Toy]

a car tuned on the dyno is tuned to run on a dyno. on the street you may be hitting untuned load points because of extra air flow which may not be tuned and have much higher numbers in the fuel table which will cause the car to run rich and have extra inj duty.

[Cjmartz2k]

Good point guilt toy

[SDEWY5]

i understand that but it is consistent with the relevant scenarios i have explained, does not ever spike unless it is dead cold and run up to temp 70+deg C and then hit, spikes, reset and then everything is normal again...straaaange, havent yet had time to drive it to check afm voltage, will def make time on sunday and see what happens. Its visible out the rear view mirror that the spike is happening, big black plume of smoke.