Injector on/off times etc

[hquick]

Hi All,
What determines the values in min injector pulsewidth etc?
Where does the small pulse threshold value come from?

Thanks

[TAQuickness]

A majority of the injector tables are based on the physical properties of the injectors themselves (i.e. how long they take to open, reach full open, and close).

[hquick]

Thanks for that info.
How do I find these details out and how do I tune my Truck to suit?
This could be having an effect on my present setup.
I am running the marine manifold and 42lb injectors. I changed the IFR but that's all.
Old injectors were the stock 19lb/hr poppets.

Thanks

[joecar]

If you had access to a scope, you may be able to measure those things:

http://img206.imageshack.us/img206/5056/injectorwaveformsfl6.png

You can see that there's a big difference between where the PCM first grounds the injector circuit and where the injector actually opens; also, a big difference between where the PCM ungrounds the circuit and the injector actually closes.

[hquick]

Thanks Joe.
That's interesting info. So....how can I get an approximate number to put into the tables in my tune?
How does everybody else work this out when they change their injector sizes?

[joecar]

It seems those numbers are not published...

those numbers could well be different for different build dates of the same model injector, and I would imagine different as temperature varied...

In lieu of borrowing a scope, I think the method is to play with those numbers until idle fueling looks good.

[hquick]

Thanks Joe....I'll ask my GM buddy how they go about it. He writes the Cal's for the current vehicles (VE Commodore/Pontiac G8). Hopefully he'll have some idea's.

[Redline Motorsports]

Thanks Joe....I'll ask my GM buddy how they go about it. He writes the Cal's for the current vehicles (VE Commodore/Pontiac G8). Hopefully he'll have some idea's.

Like Joe stated; each injector has its own unique characteristics.

The offsets are to deal with the way in which an injector "reacts" to the signal supplied from the injector drivers. The instant an injector is commanded there is a surge of fuel as the rail is at its peak pressure. Once the injector starts to move off its closed position there is a delay in its rate due to its size (windings in the injector body) and resistance to the return spring. Once the injector reaches peak open it now has to return shut. These types of physical properties are what the offsets deal with which is why every injector has its own parameters. This info is a bitch to obtain so most just keep massaging it until we get fuel trims and startup quality in line.

Bigger injectors, like 96 lb'ers are very slow responding a lazy due to there physical size. Personally I hate the FMS 42's and would rather use a 60# Moto Tron any day of the week. Its size and quality control make a huge difference in dialing them in.

Please let us know any dirt from your source!:rockon:

Howard

[oztracktuning]

Im about to go up to 125 shot of Nitrous dry and thats on top of the head/cam thats running 119.8mph 11.32. I still have the stock fuel pump and im using the white "fast 36lb" injectors. They are at around 80% DC now NA. What injectors would you suggest i get Redline? I want it to idle nice and be OK at low loads - economy is important and its cruising lean with the OS5.

[Redline Motorsports]

For a dry shot and also ease of tuning, I would use those 60"s! You might also want to look into a fuel pump as well.

If use the 42 lb "green tops" I have a feeling that you will be posting a lot about a variety of issues............ The 60's are one of the nice low speed injector with all the growing capacity you could need. They have very small windings on them which make them very responsive which is why they are more predictable to tune.

Just my .02 $

Howard