So I need to what voltage the injector opening time represents when you input your value such as 1.0mS etc with 0.1mS/ volt compensation.

I bought a pair of ID725's to give them a go as primary injectors.

The company supplied spec sheet says

1.32mS @ 10V @ 40psi pressure
1.03mS @ 12v @ 40psi pressure
0.775mS @ 14v @ 40psi pressure.

So I have come up with 0.136mS/ volt compensation from that table. But I'm not sure which opening time I use. What is the voltage for the megasquirt injector opening time. Its kinda dumb that that functionality is there but it is not actually clear how it functions.

I was going to assume it would be at 12 volts but information like this really needs to be published.

 

It is supposed to represent all voltages, as they assume there is a linear relationship between voltage and injector deadtime. Unfortunately that's not how it works in real life. There are a few ECU's out there that calculate the injector deadtime compensation this way, guessing they just wanted less to calculate. Since most alternators keep the voltage close to 14v use that when calculating the linear voltage compensation (0.55ms/volt). It will be off when voltage is low, but it's either that or have it off when voltage is where it is supposed to be..

 

Well I'm going to operate at 40psi.

I have the following data represented by inputting 1.048mS and 0.136mS/volt

1320uS @ 10V
1184uS @ 11V
1048uS @ 12V
0912uS @ 13V
0776uS @ 14V

I would probably centre it at the 12V reading if that is what the ECU worked off, and yeah I will idle between 13.2V and 13.8V typically.

Between 10V and 14V is linear enough for me that I am happy with a y=mx+c calibration.

 

Well I have been told that the megasquirt uses 13.2v for the center point by a guy on the other support forum but no one has yet confirmed it from the megasquirt documentation.

The exact value for the opening time should then be something like 0.878mS or 0.875mS or even just 0.9mS

0.136mS/v or even 0.135mS/v compensation should be close to exactly right for the practical range at my intended 40psi static rail pressure.

 

Eek, just realized I missed a decimal in my previous post... should read .055ms/ V if running at 14volts if it were calculating by a simple msec per volt function.

I'm not sure I understand how the megasquirt is calculating the deadtime function based off your numbers. Which version of Megasquirt are you working with? I just opened MS3 and it appears to have full control over the range of voltages. It denotes 13.2 as center (enter .875), then just build a % based correction curve for the other voltages.

 

Ahh, yeah I clearly misunderstood the first post. I think I was thinking it was a single inverse function. Gotta be tough when you're stupid..

MS3 even has provisions for correcting the lower non-linear range of the injector.. Impressive.

 

Yeah I use Megasquirt 2. I'm eyeing off Megasquirt 3 atm. The only things I'm not a fan of is the double decker case and the new tuning software.