Injector Lag Time

[GTR180]

hi can someone help me with understandind injector lag time...i can undertand Injector "lag" time is the time it takes for an injector to open form the time it has been energized until it is fully open but by chaning it what does it do to the way the car is tuned

thanks

[Adriano]

Lag changes with battery voltage, and the ecu must add appropriate time to the fuel table to compensate. Also if you are V.E. tuning, then the ecu calculates the amount of fuel injected, so it must add the lag time to the calculated injection time.

[GTR180]

Lag changes with battery voltage, and the ecu must add appropriate time to the fuel table to compensate. Also if you are V.E. tuning, then the ecu calculates the amount of fuel injected, so it must add the lag time to the calculated injection time.

what is v.e. tuning

[Adriano]

Volumetric efficiency, basically the ecu determines the amount of air entering the motor by measurements multiplied by a fuel table multiplied by a target air/fuel table, and this ends up with a calcultion of the amount fo fuel needed

[DVS JEZ]

all injectors have lag time, bigger injectors normally have a bigger lag time as their parts are heavier etc.

when a factory base map is created on say a power fc the lag time is set to suit the stock injectors ie 444cc for RB26.

i think the lag time for 444cc is 77

so when upgrading to say 600cc lag time 80 there is a formula to calculate the new lag time needed into the power fc.

mine with this setup is 73% .03 lag time.

if you dont calculate it right then even though your reading the correct afr the power will be low because the fuel isnt spraying at the precise time needed, for example if sprayed too early it will sit behind the valve and wont atomise correctly.

and if sprayed too late (too much lag time) the valve will be already open and the fuel wont have enough time to be fully injested into the cylinder and the valve might shut leaving fuel astray at the valve till next intake cycle,

[JonnoHR31]

if you dont calculate it right then even though your reading the correct afr the power will be low because the fuel isnt spraying at the precise time needed, for example if sprayed too early it will sit behind the valve and wont atomise correctly.

and if sprayed too late (too much lag time) the valve will be already open and the fuel wont have enough time to be fully injested into the cylinder and the valve might shut leaving fuel astray at the valve till next intake cycle,

err no, if you use the wrong latency the car will be spot on at WOT but way off at idle. the ecu calculates the amount of fuel required from its maps, then figures out how long the injector needs to spray fuel for, then adds the latency and pulses the injector for that long. so if you set the latency to 0 but the injector takes 1ms to open before it starts spraying fuel and the ecu thinks it needs 2ms of fuel at idle its only gonna pulse for 2ms, giving you 1ms of fuel, whereas if you set the latency properly it'll pulse for 3ms, giving the correct 2ms of fuel. at a constant voltage the latency never changes for a given injector, hence why it has more effect on idle than WOT

[DVS JEZ]

err no, if you use the wrong latency the car will be spot on at WOT but way off at idle. the ecu calculates the amount of fuel required from its maps, then figures out how long the injector needs to spray fuel for, then adds the latency and pulses the injector for that long. so if you set the latency to 0 but the injector takes 1ms to open before it starts spraying fuel and the ecu thinks it needs 2ms of fuel at idle its only gonna pulse for 2ms, giving you 1ms of fuel, whereas if you set the latency properly it'll pulse for 3ms, giving the correct 2ms of fuel. at a constant voltage the latency never changes for a given injector, hence why it has more effect on idle than WOT

Err no,

Lag time being off should have more of an affect at high engine speeds, Where piston speeds are much higher and the engine will rotate through a greater number of degrees during a given time interval

[PM-R33]

Speaking of lag times, how on earth do you find the correct injector latency for different voltages other than mindless google searching? I tried looking for the Nismo 555cc and I found an old thread on here that had the latency time but at what voltage I have no idea and didn't have any listings for the other voltages.

My Vipec is still on that factory injector latency and seems to run fine, but if the Nismos are a bit different i'd like to have it perfect

[Adriano]

Lag time certainly has much more effect at idle and cruise than full throttle.

If you cant find latency numbers for an injector, it can be calculated manually. I ahd to do this on one car by setting the afr at 14.7 at say 3000 rpm no load, tehn disconnect the alternator, and as the battery dies, you manually alter the lag time.

[JonnoHR31]

I tried looking for the Nismo 555cc and I found an old thread on here that had the latency time but at what voltage I have no idea and didn't have any listings for the other voltages.

My Vipec is still on that factory injector latency and seems to run fine, but if the Nismos are a bit different i'd like to have it perfect

nismo 555s are .18 higher latency than factory.

from my very vague memory factory is .63 and nismo are .81 or something like that

[DVS JEZ]

my bad... im wrong

[PM-R33]

So .18 higher at every voltage?

Vipec lists the following for the factory map:

6V - 3.2ms

7V - 2.5ms

8V - 1.9ms

9V - 1.5ms

10V - 1.25ms

11V - 1.11ms

12V - 0.945ms

13V - 0.87ms

14V - 0.743ms

15V - 0.6ms

Edited September 13, 2010 by PM-R33

[JonnoHR31]

dunno bout every voltage but it should be close enough. im assuming when you enter +.18 into the power fc it just uses the same correction accross the board

[Don Dada]

Anyone know a definite lag time value for Nismo 555cc pink top feed for rb26dett ?

[Don Dada]

Ok guys i believe nismo uses the same denso injector as tomei so may be these values can work>

http://www.tomei-p.co.jp/_2003web-catalogue/efr_set-from_top-menu/efr_index_fuel-line_rset.html

I see alot of guys use .71 for the yellow 555cc side feed nismo injectors also which kinda confirms it is the same injector as tomei because they recommend the same value

so i guess .61 will work for the pink 555cc topfeed ???

[PM-R33]

Are you using a Power FC or something else?

I never really found a definete answer about what to set mine to.

[scotty nm35]

I really don't think you can give definite answers anyway, the lag changes dramatically depending on the injector voltage so every application will be different. Use the graphs supplied to give you a ballpark figure and adjust it from there to give your engine a good idle I guess.

[DVS JEZ]

lag/latency can be set up at idle, if your AFR's are unstable at idle try adjusting lag time and monitor what happens.

the main reason there is a formula to work out when changing to bigger inj etc is so you can get the tune close so the vehicle can be driven to get a tune.

[Don Dada]

Are you using a Power FC or something else?

I never really found a definete answer about what to set mine to.

Yea pfc for me

You're using 555cc yellow side feeds?...If so i'd focus on the 14v value because basically this is the pretty much the operating voltage with the car idling so from the values you posted earlier i'd say youre very close ie.

14v -0.743ms..... nismos> 0.71ms

what do you have it set on now?? how does it idle?

[PM-R33]

Yeah 555cc yellow side feeds.

At the moment it is just set to the default value on the Vipec as I listed above.

Idle isn't perfect but that's probably a lot to do with my tune lol.

Might change atleast the 14V value to 0.71 and see if it likes it.