Reached 100% fuel injector duty

[ITR136]

Afternoon,

I own a dc2r and recently installed an injen cold air intake. For reference the car has full exhaust (toda headers, high flow cat and hks cat-back) along with a power fc ecu.

The rev limit before the intake was installed was set at 8500rpm and the inj. duty only hit 95% at 8500rpm. Now with the new intake it hits 100% at rev-limit (power fc hand controller said 7700 rpm)

After I installed the intake I straight away lowered the rev-limt from 8500 to 8000rpm because I thought this may be an issue but didn't expect to see it hit 100%. Also the car does not show any check engine lights.

So my question is.....do I only need to upgrade the fuel injectors or should I do the fuel pump as well. A friend has a Walbro 255lph for sale and I've read a lot of people use that. I am not sure whether the oem pressure regulator, rail and pump can work with upgraded injectors.

Thanks for your help in advance!

P.S I am new to forums and do not know how to insert a photo into a post, so I will just attach it.

100% inj. duty.jpg

[wpg81]

Make shore your intake air temp sensor is connected. Default setting will richen up the air/ fuel ratio. Side note 90% is normally maximum limit for duty cycle for injectors to allow for any unusual circumstances.

[tinkerbell]

no you need to increase your base fuel pressure, which is set by factory at around 42psi.

i run this on my engine:



Aeromotive A1000

do this before spending big cash on injectors...

but you sound like you need to factor in a dyno tune too...

[ITR136]

Thanks for the idea wpg81 the intake air temp sensor is working fine I monitor the power fc hand controller all the time.

Hey tinkerbell what is that; a FPR? I did read last night that if the fuel pressure is increased it may cause the injectors to be under too much stress. What are your thoughts?

Yes I think a dyno tune is a great idea. I would like to see 130 kw atw if possible

[ITR136]

I spent pretty much 3 hours last night researching this issue and here is what I found:

OEM ITR injectors = 240cc (same as most b series). Prelude 97+ = 290cc. These could be a great plug and play as no resistor box is required unlike the 96 model. DC5 Type S = 310cc but not sure if they work being off a K series... RC 270 or 310cc are available but quite expensive.

ITR fuel pump and I presume rail and FPR can handle 220 whp so I am fine at 170 whp.

Therefore a larger fuel pump is not required and if a Walbro 255 lph was used I would need to upgrade the FPR as well. Fuel rail is not necessary and basically just for looks.

So what I am thinking is replace only the fuel injectors with larger ones. I know some people use RC 310cc but they are expensive and I am not sure if my car with stock internals could use anywhere near that (I am thinking of going all motor one day though). I've also heard that using too large injectors is just plain dumb, i.e. RC 310cc in stock Integra LS (GSI) etc.

Would you guys recommend OEM Prelude 290cc injectors as they would probably flow fine and be nowhere near the 100% duty. Would the ridiculous Honda OEM price for the Prelude 290cc be close to the RC 310cc anyway?

If anything I wrote needs correcting please inform me

[tinkerbell]

you read that increasing FP will stress the injectors?

um, what would stress the injectors MORE is running at 90+ duty cycle.

you only need to bump the FP up to 52ish PSI to get the added headroom on the 240cc ones, so no excessive "stress" will be placed on the standard injectors.

i run my ID 725cc injectors at 75 PSI and my injectors are at around 30% duty cycle... (but i am making over 250hp from a 1995cc engine... so not really the same situation as you...)

but if you don't want to get a cheap adjustable FPR, then go ahead and muck around with buying expensive injectors... you will need a dyno tune either way...

and your dyno tuner will happily charge you more $$$ to dial in your fuel map to a set of injectors compared to tweaking your FPR pressure to get better AFRs...


bottom line:

you need to increase your fuel pressure.

[ITR136]

Just found an interesting article on Hondata's website stating that "Honda runs their injectors to 100% to get accurate delivery at part load and revs, which in theory will help emissions, economy and drivability".

Good news I do not require anything to be done to my car. I completed multiple runs and changed the rev-limit each time to determine where the duty cycle was maxing out. Note that the achievable result is never exactly the same as the set rev-limit. The results were:

7000rpm = 62.1%
7250rpm = 75.5%
7500rpm = 78.5%
8000rpm = 84.5%
8250rpm = 92.2%
8500rpm = 92.6%

This was confusing to me and I analysed what figures I received. All runs were on the same flat road but I remembered that when it topped out at 100% I was travelling up a light to moderate slope to enter the highway. So obviously the loading of the engine due to the gradient in the road caused more fuel to be added into the mixture; something I have never thought about.

[tinkerbell]

So obviously the loading of the engine due to the gradient in the road caused more fuel to be added into the mixture; something I have never thought about.

next, try it with 4 full grown adults in the car + 10 bags of sand in the boot...

then you will know what "under load" means...