Injector Lag?

[frozenwaffles]

does anyone know anything about setting up injector lag, beyond just inputing the numbers from the manufacturer?

i've been mapping the car but having problems getting a good idle and mpg and the problem seems to be injector lag. i get the car setup ok, it drives ok, afr at idle 14.7 within a few points with no o2 sensor feedback. if i increase the lag a half point eg 0.18ms to 0.24ms my afr's go rich, remap the car and the car drives and idles better. i'm up to +0.28ms so far with the manufacturer saying it should be +0.19ms and the car is a lot better.

does anyone know what the professionals do to setup injector lag?

i'm thinking what's happening is the injector is being opened too late by the ecu because the setting is too low, thus spraying the back of the valve as it closes. this pool at the back of the valve doesn't burn on this ignition nor on the next, it's just wasted fuel (bad economy). the wideband doesn't pick this up because it cant sense unburnt fuel, spray the sensor with petrol and it doesn't read rich. so, the lag is made greater and the injector fires earlier, this time it gets more atomised fuel ito the chamber for the combustion and my afr's go up, readjust the injector duty and the whole thing is timed a lot better so the car runs better.

does this sound ok?

i'm wondering if this should be repeated until the lag adjustment causes it to go leaner rather than richer. seems logical to me.

any input would be greatfully accepted, unless it's lies

[SATO GTS]

are you trimming the std inj's or are you installing new larger injector's

If they are std then leave the setting's as std

What ecu are you using?

[frozenwaffles]

sorry for thre lack on info...

RB25DET - nismo 555cc injectors - power fc

current setting are 50% correction and +0.40ms latency!!! has never idled so well and runs around 15 AFR on light load and drops nicely as it moves lower on the map...

oh and on idle its slightly rich..around 14.2

[Mr. Untouchable]

50% correction you say? rb25det stock injectors are 370cc, you have 555's, the correction "should" be 75% yes?

740's 50%?

[JonnoHR31]

should be 66.6% (66.5 in power fc as it rounds to half %) and +18ms latency correction

[frozenwaffles]

i know what it should be..thats not hard to find...

i am thinking that maybe the nismo 555s are not 555cc?!?!?!? i have found reports of this is a few places around the world... dont really feel like pulling them all out to get tested but i might have too...

i think this is the begining of finding something with my car that has never been quite right...

[Mr. Untouchable]

old injector size / new injector size - yeah 66.5, not 75%... woops

but not 50%..

so does this basically lean things up?

haha i'll leave this to the tuners!

[JonnoHR31]

have you tried it with those settings? if you bought nismo 555s theres no way they'd be flowing over 700cc (which would need the 50% correction)

the fact that you've had to add so much latency correction over the recommended settings means your size correction is too low. more positive latency correction adds more fuel, which makes up for your size correction being 16% too low

[frozenwaffles]

how does more injector latency change the amount of fuel they flow??? i thought latency changes the time the injectors fire in relation to the CAS signal and also spark timing???

if the injectors fire too late then there could be fuel atomising on the back of the valves as they close and waste fuel.

with the normal settings for the nismo 555s i can always smell fuel a little around the car..particularly on idle.

however with the new settings i smell less fuel...

[JonnoHR31]

latency is the time it takes for the injector to open and start squirting fuel. the higher the latency the more time the injector has to be pulsed with no fuel flowing (while its opening and closing). so therefore if your telling the ecu it takes ages to open and close it'll pulse for longer to inject the same amount of fuel

[frozenwaffles]

well thats a logical explanation...hmmm interesting...

[SATO GTS]

What fuel pressure are you running ? Cause it will have a huge effect on the flow of the injector's.

any thing about 45 psi and they run extremly rich .

[Guilt-Toy]

every time i have tuned a car the injector settings have been no where near where the internet people tell me it should be.

The sooner you start using your own head and start working it out yourself instead of worrying what people say on here the quicker you will get the problem solved and you will learn how to tune cars alot faster.

I like to keep the injectors as close to 100% as possible. I don't care what injector it is. after you do 10 or 20 of them you start to see a trend in what works and what does'nt

[SATO GTS]

could not agree with you more GT