Making my own Calc PID

[andrewjamesbond1]

Hey guys, I need some help with the scan tool and making my own PIDs. Probably should be in the Scanning section of the forum, but I figured with it being diesel related, I would have the best of the best helping me. I have tried reading Ross's write up on PIDs, but am unsure exactly how to do it.
I am looking to make a couple PIDs. One I would like to log is my fuel rate per rpm. So I would like to take the Commanded Fuel Rate in mm3 and divide it by my RPM. Reasoning is to see at what point of lugging the engine at low RPM's becomes not fuel efficient. For example, is it better to run in 5th locked at 44 mph or is it better to run in 6th?
Another PID I want to make is Boost instead or reading absolute pressure. So I want to take the manifold pressure and subtract it from the baro. If anyone can help me out, I would greatly appreciate it!

[joecar]

What are the exact pids and equation for the intended fuel rate pid...?


For boost/vacuum, see attached calc_pids.txt file, copy it to the folder My Documents\EFILive\V7.5\User Configuration.

[andrewjamesbond1]

Thanks joecar!
For the fuel rate pid, I was going to use commanded fuel rate, mm3 and engine speed, rpm. Basically take mm3/rpm = my fuel rate pid.
I am going to check out your txt file as soon as I get back to my computer =D

[bballer182]

Hint. Instead of using commanded mm3 use a number generated buy using pressure and pulse width. Commanded mm3 has nothing to do with actual fuel flow.

[andrewjamesbond1]

I kinda wondered since fuel pressure is related to rpms.... thanks fpr confirming my suspcisions bballer!

[bballer182]

I kinda wondered since fuel pressure is related to rpms.... thanks fpr confirming my suspcisions bballer!

Kind of but not really. You can command 180Mpa at 1000rpm or 20Mpa at 3000rpm if you want. So you have to know the equation of flow thru an orfice. Can't remember it off the top of my head but it is easily found with a quick Google search. And remember use ACTUAL not COMMANDED data for your pid.

[andrewjamesbond1]

Kind of but not really. You can command 180Mpa at 1000rpm or 20Mpa at 3000rpm if you want. So you have to know the equation of flow thru an orfice. Can't remember it off the top of my head but it is easily found with a quick Google search. And remember use ACTUAL not COMMANDED data for your pid.

Sorry, I guess when rereading what I wrote, Fuel Rail Pressure is not really dependent of RPM lol. I knew you could command any FRP within reason, but don't know why I just didn't say that lol... Here is an equation for finding a flow rate with a known flow rate at a certain pressure:

The following formula can help you determine the injector’s flow rate with a change in the fuel pressure’s set point:

Q2 = {Square Root (P2/P1)} x Q1

Q1 = Original injector flow rate (lbs/hr)
Q2 = Injector flow rate at modified pressure (lbs/hr)
P1 = Original fuel pressure set point (psi)
P2 = Adjusted fuel pressure set point (psi)


Still looking for an equation that deals with Pulsewidth to find the correct fuel injected.

[killerbee]

mm3 fuel rate is already per stroke. Dividing it by rpm will produce a number that has no real meaning.

fwiw.

[andrewjamesbond1]

Thanks for the info killerbee, wasn't entirely sure of the actual units behind commanded fuel rate.
I guess what I am trying to get at is a fuel flow rate in mm3/sec, or min. That way I can see "Hey, in 4th gear at such and such RPM, I am using 30 mm3/sec, but in 5th I am using 33 mm3/sec, so its better to stay in 4th at this RPM"

So I was thinking that:

My flow rate = Commanded mm3 * RPM * Conversion Factor * Conversion Factor

mm3/sec = mm3/stroke * Rev/min * (1 min / 60 sec) * (2 Strokes / 1 rev)

That would be the commanded fuel flow rate for mm3/sec. Now since commanded fuel rate is an arbitrary number (thanks for the heads up again bballer), instead of commanded fuel rate, I would substitute in another equation for actual fuel being injected into the cylinder using fuel pressure and puslewidth. What are your guys' thoughts on this?

[killerbee]

I would suggest making a pid that uses pulse, pressure, rpm and VSS. mm3 is a fairly worthless number to try to standardize. I prefer to think of it as a unitless number, with no real correlation to volumetric flow rate as would be measured by a flow meter.

Pulse * pressure(squared) is more representative of actual fuel volumetric flow rate, for economy purposes.