why are my injector duties so high?
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why are my injector duties so high?
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
-Chance
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dominican boost junkie
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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
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
#11
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
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
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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
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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
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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
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
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