So I had my car tuned last July and noticed that my max injector duties are hitting 85 percent and more the colder it gets. Mods are in my sig but I am running a rp fuel pump and 1300cc secondaries with the stock 550 primaries. So my question is why is my injector duty so high when looking around on this site people seem to be able to make so much more power than me with the same fuel set up?

-Chance

 

did you rewire the fuel pump to increase voltage?

 

No I have not. Would this really make that big of a difference? I am seeing people on here who can easily get 400rwhp out of my set up.

 

still running stock base pressure?

 

400 on stock seq twins? um....maybe one or two people have pulled that off, but that definitely is not something that happens "easily"

my best pull so far is 380 on the stock twins (non seq)

i think your 317 pull sounds about right for your mod list.

 

Yes rewiring the fuel pump helps quite a bit. Have your injectors been cleaned at all? That could be another reason. Maybe old fuel filter. Decreased fuel pressure. And lastly maybe overly rich tune.

 

Rewire the fuel pump for better result...

 

Do you have the stock pump? Put a Denso supra pump plus the rewiring. I have about 80% duty cycle with 850/850cc injectors. I have the denso pump and rewire. I am putting out 365whp. This may a huge difference.

Also replace old fuel filter, people tend to forget this. And put a fuel pump regulator. You should be able to see over 400whp with your setup

 

^^ with the stock twins??? right...

As theorie said just because a couple of dudes pulled that off it does not make it the norm.

 

yea he's running the stock twins. And for the OP I agree....new pump, check wiring, check pressure, and if all else fails get the injectors cleaned. There's not much else too it

 

if you happen to be getting lower than normal fuel pressure due to voltage pump age dirty filter ...whatever, when you fix it, unless you retune, the duty cycle is not going to go down any.

you can tune to cover a slightly weak pump or pressure that falls off on the top end a bit by increasing the duty cycle. and 85% is not terrible

 

^^it is if he's got 1300's with stock twins and at 13 psi... I got 1300's and im at 80-85% with a GT35R at 15 psi, 10.9-11.2 AFR (rich). Actually I think my injector duty cycle is a little high as well...

 

Sorry I meant out of my fuel set up, I am not trying for any miracles. I am just trying to figure this out before I go single. This is my first "hands on" car so I am learning as I go and this didnt make sense to me.

The injectors were cleaned and flow matched a year ago. I will replace my fuel filter but it looks like I wont do me any good since I will need a tune to get the duties back down and I am going single this winter so I will take care of it all then.

Thanks for all the replies now I dont have to wonder why my car is getting such high IDs.

-Chance

 

You should get Chuck Wesbrook notes. They explain how the PFC allocates fuel to the injectors and what "available injector on time" is. Then, calculate the injector duty derived from the msec values of your map cells and compare it with your logged injector duty in those cells. They should match.

- Sandro

 

Anecdotally, I noticed my duty cycles changing by a few percent (like 2-5%) when the AFRs were changed by a few tenths. For example, when I went from 10.5:1 AFR to 11:1 AFR under pretty much same conditions (air, water, fuel temp) my duties went from 87% to 83% @ ~7500 rpm. Remember, your injector duties will be higher at higher revs and richer fuel... I don't feel it's a really linear (actually inversely proportional) relationship between AFR & duty cycle, but it's probably close enough to get a baseline tune and go from there...

FWIW I have 550cc pri/1300cc sec injectors w/ "Supra" fuel pump and stock wiring.

EDIT: It's no coincidence you're getting richer AFRs when it's colder... most unmodded PFC maps will add more fuel when air temps are cooler. Depending on how good/bad your IC/intake setup is (core, ducting, plumbing, it all counts!) you may be bringing in colder or hotter air than the air temp sensor will indicate. BTW that sensor is a piece of ****, it is very slow and generally does not reflect the true air temperature going into the engine (do a search). Check out the INJ Vs. Air temp correction tables (with a FC-datalogit) to see what I mean. It will add a few percent more fuel when it's chilly and hence your richer running car and higher INJ duty. The idea behind it is to add more fuel to colder denser air to keep AFRs the same... but it's not very well dialed in with the "untuned" maps... every car is a little different. you should check out cewrx7r1's notes for more info...

Hope this helps