MoTeC Global Forum

Hi,

I have 2 injectors per cylinder on my M400, so both injectors always feed fuel. How does the ECU know this when using quick lambda. If Q/Lam thinks the A/F needs changing by 3% then it will change the pulsewidth to suit affecting both injectors so changing the fuelling by 6%.

Can I compersate for this.

Thanks.

lawnmower wrote:Hi,

I have 2 injectors per cylinder on my M400, so both injectors always feed fuel. How does the ECU know this when using quick lambda. If Q/Lam thinks the A/F needs changing by 3% then it will change the pulsewidth to suit affecting both injectors so changing the fuelling by 6%.

Can I compersate for this.

Thanks.

Lets say the injectors are the same ize.
So injector #1 is 50% and injector #2 is 50%, both in total provide 100% of the fuel.
For injector #1... 3% of 50% is 1.5%
Same for injector #2.

Add injector #1 and injector#2,,, 1.5% + 1.5% = 3%
...pfm

If the pulsewidth needs changing the quick lambda will do it. But it will do it for both injectors which will double the needed change.

So the question is still can I compensate for this, the Q/Lam needs to know there are 2 injectors to accurately change the fueling but I am not aware of anything in the software that reletes to this.

Holmz wrote:
Add injector #1 and injector#2,,, 1.5% + 1.5% = 3%
...pfm

In your example above you have illustrated the point I am trying to find an answer to, if inj#1 and #2 are added togeather I will get double the effective flow change change that I want. Not sure of your point?

lawnmower wrote:...In your example above you have illustrated the point I am trying to find an answer to, if inj#1 and #2 are added together I will get double the effective flow change change that I want. Not sure of your point?

I am not a very good teacher, and perhaps we are understanding each other.

Are your injectors wired together, or does the ECU treat them separately?

Lets say that your injectors #1 and #2 are both 300-cc.
Now replace the two smaller injectors with a larger single 600-cc injector...

How would having a single injector change how the system works?

The injecotrs are wired togeather so the ECU will see them as 1, so Q/Lam is calculated on the basis that there is 1 PW. When it sends the corrected PW it will do so to both injectors so doubleing the fuel correction. Does this make sence? I need to know of the way around this for the Q/Lam to work properly.

When I brought my injectors I was not aware of the various manafacturers of VERY high flow injectors so I settled for 8 Bosch 1680cc, so you can see the more common normal size injectors that are availiable are way to small. Given the choice again I would buy a single set of 2200cc or similiar.

If the injectors are wired together the ECU will only see one injector of the combined size.

The Q lambda will work fine. No compensation is needed.

lawnmower wrote:The injectors are wired togeather so the ECU will see them as 1, so Q/Lam is calculated on the basis that there is 1 PW. When it sends the corrected PW it will do so to both injectors so doubling the fuel correction. Does this make sense?

NO - It makes no sense to me.
In your mind you got double - but you do not understand the maths

A 3% change of 2 injectors is 3%
A 3% change of a single injector is 3%.

I have done the maths and verified that.

lawnmower wrote:I need to know of the way around this for the Q/Lam to work properly.

In your mind pretend that there is a single injector.
Now when you add 3% you get 3% change in AFR.
How it works in your mind will now match what happens in real life.

try this...
Take a single 1000-cc injector. Run it for a minute, how many cc's do you get?
Take a single 1-cc injector. Run it for a minute, how many cc's do you get?
No wire 1000 of the small 1-cc injectors in parallel... Run them for a minute, how many cc's do you get?

Ok starting to make sense now, just as well I asked. Thanks.

lawnmower wrote:Ok starting to make sense now, just as well I asked. Thanks.

It would be interesting to know if anything can be done when using 2 injectors in a hi/lo configuration...
I suspect it means a sharp pencil and working it out by hand???

The ECU does not need to know anything about the injectors or size apart from calculating fuel used.

The great thing about working in lambda is that Lambda .9 is 10% rich and lambda 1.1 is 10% lean.

Since most injectors are operated through their linear flow range. The ECU looks at the current lambda value then makes a calculation based on the current main table fuel value used.

This will confuse things a little but quick lambda only makes a 80% change of the total change required.
So the If its 10% lean it will make a 8% change to the fuel table value.