Injector Response Times

[Scooby]

Keen to know if anyone has experience with this. For example the Sard 700cc single hole inj has a shorter response time than the twin hole 800.

Hi Octane tell me that it relates to the time taken for the injectors to react to a command from some ecus, but that with a PFC the 700s and 800s will have no difference in response time.

Cheers

[T04GTR]

you cant change how quick they open. doesnt matter if its a power fc or a 12v battery.

[Beer Baron]

yeah that is complete nonsense. the lagtime is not set by the ecu BUT some ecus (like PFC) will compensate for it.

but still I would choose the 700s over the 800s unless you really need all of those 800cc. the 800cc lag time is twice that of the 700s.

[Scooby]

yeah that is complete nonsense. the lagtime is not set by the ecu BUT some ecus (like PFC) will compensate for it.

but still I would choose the 700s over the 800s unless you really need all of those 800cc. the 800cc lag time is twice that of the 700s.

I think they were saying it's the time that the injector takes to operate in response to the ecu signal rather than the inherent opening / closing speed or anything else.

OK, if the PFC compensates for it why does it matter what the lag time is?

What real world difference will it make?

[RedDrifter]

Can't say with regards to the power fc but with the stock nissan ecu's adjusting the lag times affects the idle mixture.

Too much correction it will run too rich and not enough too lean.

[GeeTR]

Can't say with regards to the power fc but with the stock nissan ecu's adjusting the lag times affects the idle mixture.

Too much correction it will run too rich and not enough too lean.

Thats odd, as the injector open time isn't being touched.

This topic comes up a lot. From my research, the lag time has no effect.

When in batch firing mode (non sequential) your firing a portion (half or 1/4 depending on available injector drivers) against a the back of a closed inlet valve anyway, so im not sure how a few ms of difference is going to effect anything.

I'm still not sure on the use of the feature. A lot of ppl simple set it to zero and tune

2 cents

[STATUS]

latency or lag is quite important to maintain accurate injector timing as an inneffiecent injector with large lag times and no correction via the ECU robs you of "effective" fuel delivery.... poor tuners will tend to leave this at zero as they dont actually understand the basics of tuning.... they just fiddle with numbers.

[saliya]

Keen to know if anyone has experience with this. For example the Sard 700cc single hole inj has a shorter response time than the twin hole 800.

Hi Octane tell me that it relates to the time taken for the injectors to react to a command from some ecus, but that with a PFC the 700s and 800s will have no difference in response time.

Cheers

Hey,

With a PFC you can apply different compensations, that might be what they mean. So

different lag times can be accounted for.

with my car, 700cc sards, going from 0ms compensation to 0.18ms compensation made it slightly richer at all

RPMS I've measured at (below boost threshold, I haven't measured at or above without the correction).

I'm guessing this is related to a bit of black magic - valve position will be affecting gas volume and

velocity, and the fuel pulse's position in relation to _that_ is affecting the mixtures. Definitely a small but

observable effect (I removed the correction and retested )

I guess this means that the PFC has fully-sequential injector control? Otherwise, why would it have

the space for correction and why would correction make a difference?

Regards,

Saliya

[Apex Trudger]

I guess this means that the PFC has fully-sequential injector control? Otherwise, why would it have

the space for correction and why would correction make a difference?

Correct, Seq injection as far im aware

latency or lag is quite important to maintain accurate injector timing as an inneffiecent injector with large lag times and no correction via the ECU robs you of "effective" fuel delivery.... poor tuners will tend to leave this at zero as they dont actually understand the basics of tuning.... they just fiddle with numbers.

No offence, but seems like a blanket statment. As i mentioned, the lag setting is purely a timeing issue; it doesnt change in any way the amount of fuel being metered past the pintle. So considering any fuel injected will eventurally make its way into the cylinder on the intake stroke, can you explain how the the lag setting afffects AR ratio's? Im eager to learn and would appreciate a correcting to my current understanding. "Full rotation out" early days EFI batch firing and current seq inj is confusing; the only angle i can think of is that, injecting the fuel at a specific time VS vale opening could effect swirl and tumble, effectivly changing the effectivness of mixing.. but then there would be a totally diff requiremnt through the rev ranges. I dont belive theres a injector latenct VS RPM in any AM ECU.

Thanks in advance

[GeeTR]

^^ Spot on, my thoughts / questions exactly ^^

[saliya]

No offence, but seems like a blanket statment. As i mentioned, the lag setting is purely a timeing issue; it doesnt change in any way the amount of fuel being metered past the pintle. So considering any fuel injected will eventurally make its way into the cylinder on the intake stroke, can you explain how the the lag setting afffects AR ratio's? Im eager to learn and would appreciate a correcting to my current understanding. "Full rotation out" early days EFI batch firing and current seq inj is confusing; the only angle i can think of is that, injecting the fuel at a specific time VS vale opening could effect swirl and tumble, effectivly changing the effectivness of mixing.. but then there would be a totally diff requiremnt through the rev ranges. I dont belive theres a injector latenct VS RPM in any AM ECU.

Thanks in advance

Hey,

It's an interesting phenomenon, that's for sure...

There is definitely a measurable difference and it's easily-repeatable on my car.

Unless my car's a weird one, anybody should be able to repeat it on their RB26?

Get a wideband, start the car, take some readings, change the correction factor,

observe the results.

Maybe the idea that equal opening times == equal fuel delivery isn't always correct?

If I had to guess I'd say the air pressure pushing back against the fuel is slightly-different

depending on valve position (i.e. slightly lower when it's open and the cylinder is filling,

slightly higher when it's closed).

That could mean that more or less fuel would be delivered in a given pulse width

depending on valve position. That is, firing at a closed valve delivers less fuel

than firing for the same amount of time at a filling cylinder.

That's just a guess to explain my observations, though

Maybe the underpants gnomes are stealing some fuel ???

Regards,

Saliya

[Warpspeed]

Some amazing statements above !!!!!

Now suppose an imaginary injector takes one millisecond to open, and one half millisecond to close.

Now imagine you feed it with a two millisecond long pulse. Nothing happens for one millisecond, because of the opening delay. Then it flows for one and a half milliseconds. Think about it.

What happens if you feed it with only a one millisecond pulse? It is not going to begin flowing at all, before the pulse is gone.

The problem with sluggish injectors, particularly very LARGE sluggish injectors is that they can be terrible for idle quality. Large injectors obviously need shorter flow times for the same fuel delivery volume. At idle, fuel delivery is small, and large slow injectors can behave very erratically.

Always use the smallest size injectors that will work with sufficient safety margin. And if idle quality is important, faster injectors are always an advantage.

A good rule of thumb for a six cylinder engine is Injector CCs = flywheel horsepower, at 100% duty cycle.

[GTRgeoff]

Yes I'm a bit amazed by the lack of understanding above as well. Especially if some of you guys are fiddling with tunes.

An injector is an electro-mechanical device with a mass that has to be moved by EM force to open and close. The larger the mass/smaller the force, the longer it takes to respond, which is defined as lag compared to the standard item in the PFC.

If you don't adjust the lag then it will take longer for the injector to open, so the injector is still opening when peak open time is being measured so less peak fuel is delivered, plus the valve could be closing before the fuel is delivered due to slower closing time and causing significant tuning difficulties by pooling the fuel and the subsequent effects could be lean knock, rich knock or even worse hydrostatic lock in the engine with catastrophic effects.

So it is critical to correct for both injector size and for lag.

The computer doesn't have any way of correcting lag automatically, so you have to do it. It then automatically starts the open/close sequence to deliver the correct peak open times in relation to the rpm and valve times BUT you will have an environment that needs to be fine tuned with injector corrections against logged Lambda data.

I'm currently using the Innovate Motorsports LM1 and LC1 modules with Bosch wideband O2 sensors for tuning the racecar and GTR, plugged direct into the FC Datalogit black box (for tuning all models of PFC) and I've found it to be both educational and a hell of a lot better money spent than handing over to some of the tuners who charge a squillion.

[T04GTR]

i think given that the powerfc is tuned via a direct ms input i think. it uses the lag time to acuratly compinsate for the injector.. ie. injector takes .5ms to open. so given a 2ms comand it will only efectivly be open for 1.5ms.. not 2ms.

where as if you adjust the power fc to the .5ms lag time it will automaticly add the lag time to the comand so you get a full 2ms fuel injection point. make sence?

and as far as im aware the powerfc doesnt have a injection end angle adjustment.

summing up. the lag time adjustment simply adds this time to the injection time per event.

[RedDrifter]

i think given that the powerfc is tuned via a direct ms input i think. it uses the lag time to acuratly compinsate for the injector.. ie. injector takes .5ms to open. so given a 2ms comand it will only efectivly be open for 1.5ms.. not 2ms.

where as if you adjust the power fc to the .5ms lag time it will automaticly add the lag time to the comand so you get a full 2ms fuel injection point. make sence?

and as far as im aware the powerfc doesnt have a injection end angle adjustment.

summing up. the lag time adjustment simply adds this time to the injection time per event.

Thats pretty much how the stock ecu does it. I had no idea if the FC did the same though.

[Scooby]

Yes I'm a bit amazed by the lack of understanding above as well. Especially if some of you guys are fiddling with tunes.

An injector is an electro-mechanical device with a mass that has to be moved by EM force to open and close. The larger the mass/smaller the force, the longer it takes to respond, which is defined as lag compared to the standard item in the PFC.

If you don't adjust the lag then it will take longer for the injector to open, so the injector is still opening when peak open time is being measured so less peak fuel is delivered, plus the valve could be closing before the fuel is delivered due to slower closing time and causing significant tuning difficulties by pooling the fuel and the subsequent effects could be lean knock, rich knock or even worse hydrostatic lock in the engine with catastrophic effects.

So it is critical to correct for both injector size and for lag.

The computer doesn't have any way of correcting lag automatically, so you have to do it. It then automatically starts the open/close sequence to deliver the correct peak open times in relation to the rpm and valve times BUT you will have an environment that needs to be fine tuned with injector corrections against logged Lambda data.

I'm currently using the Innovate Motorsports LM1 and LC1 modules with Bosch wideband O2 sensors for tuning the racecar and GTR, plugged direct into the FC Datalogit black box (for tuning all models of PFC) and I've found it to be both educational and a hell of a lot better money spent than handing over to some of the tuners who charge a squillion.

thanks everyone for the input.

Geoff's explanation is what i understood to be the case based on the effect i'd expect 'lag' to have in this sense and why it makes sense that the 800 sards have a slower response time than 700s.

so...correct me if i'm wrong but lag duration is neither good nor bad, it just needs to compensated for correctly.

Edited September 8, 2007 by Scooby

[T04GTR]

exacly.

the twin hole injectors are slower to respond usualy.

[STATUS]

Correct, Seq injection as far im aware

No offence, but seems like a blanket statment. As i mentioned, the lag setting is purely a timeing issue; it doesnt change in any way the amount of fuel being metered past the pintle. So considering any fuel injected will eventurally make its way into the cylinder on the intake stroke, can you explain how the the lag setting afffects AR ratio's? Im eager to learn and would appreciate a correcting to my current understanding. "Full rotation out" early days EFI batch firing and current seq inj is confusing; the only angle i can think of is that, injecting the fuel at a specific time VS vale opening could effect swirl and tumble, effectivly changing the effectivness of mixing.. but then there would be a totally diff requiremnt through the rev ranges. I dont belive theres a injector latenct VS RPM in any AM ECU.

Thanks in advance

Actually you are incorrect if the injector fires for 2.2ms and the lag time is 0.8 the injector is only injecting fuel for 1.4ms FACT. This is why many jap tuners do not like some SARD injectors as they are quite inefficient.... this misunderstanding all actually came up in a course i did recently with one japans top ECU manufacturers and tuners. LAG time is not affected by RPM but by the load thatis put on the engine. The lower the load is on the engine the larger the lag time will be.

LAG TIME or LATENCY is the time it takes from when the ECU grounds the injector circuit to actually delivering fuel through the injector. A quick look at a scope will reveal all you need to know about lag or latency.

[GTRgeoff]

Which is why we correct for it in the page 5 settings on the datalogit software, but there is a bit more to it than that square wave pulse. The lag component will be a ramp of sorts with a slight overshoot and then held open (unless the pulse is very small) until closing which is another ramp as response is never instantaneous.

[TTOBES]

I can see that a lot of tuners would not see this as a major concern. They are aiming for a specific A/F ratio and the injector duty cycle is set to achieve that ratio. The fact that they loose the time/fuel taken to open and close the injectors is invisible to them and they compenste for the lag, without realising, by extending the duty cycle slightly.

URAS, did your tuner say the lag compensation was simply added to extend the duty cycle, or added to the start time to bring the event forward to correct the timing issue??

Also, how does the load placed on the engine affect the lag time??

I would have thought an injector would take x amount of time to open regardless of load...