WTF Min injector pulse

[sikhabib]

What is the point of having this ?? i have been chasing my tail for about a week trying to find out why my car run rich on decel. I finaly discovered it was cause the min injector pulse was to high (stock settings and stock injectors). IF the car is requesting a certain pulse width for the fueling it needs why do you have to add to it (and make the car go rich) to make it above the min value

[SUTTERERMAN85]

could also be for DFCO maybe i am not really sure just an idea

[Shifted]

Would the injectors not respond to a pulse less than a certain width? It takes time for a valve to open and close, if the pulse wasn't long enough, the valve may not have time to respond. That parameter may be so the ECU does not try to send a pulse that is quicker than what the injector can respond to...

[EC_Tune]

Would the injectors not respond to a pulse less than a certain width? It takes time for a valve to open and close, if the pulse wasn't long enough, the valve may not have time to respond. That parameter may be so the ECU does not try to send a pulse that is quicker than what the injector can respond to...

Exactly.
Every injector has a minimum pulse width. Pintel style has the slowest rate as they have more mass to move.

If you have the latest style injectors the minimum pulse width is much lower on them giving the injector more "bandwidth".

Below the minimum pulse width the injector is unstable in it's fuel delivery as well.

[Chris@HPTuners]

EC is correct, GM have all the min pulse width stuff to compensate for the large non-linearity at very small pulse widths.

[jimmyblue]

But isn't that the offset value table's job, not the Min PW?
Seems like min doesn't compensate anything, it's just a
clip limit?

[Chris@HPTuners]

the offset compensates the opening delay and the volume of air trapped in the injector nozzle (the time from when you ask the injector to fire to when it actually starts squirting fuel). The short pulse and adder tables compensates the fuel delivery for a given pulse width (in an attempt to keep it linear). You are correct that the min pulse width is a clip, basically it is saying that below this number cannot be compensated so don't go below it.

when you change to very large injectors usually you need to lower the min pulse width to maintain stoich idle but your huge injectors are horribly non-linear at such small pulses. Who knows what the right numbers are...

[sikhabib]

ok thats makes sense. Would you recomend changing the factory setting for min pulse width lower if need be or is that factory limit the lowest you should go to have consistent fueling.

Im in the process of tuning my Ve table in open loop and im running really rich on decel cause of this. I do plan on turning DFCO back on once im happy with everything so its not a biggie but if possible i would like to lean it out a little so my ve will be spot on

[Dragman]

I have also put in larger injectors (42#). I am tuning VE right now and have noticed that I am running at -15 or so in decel. Seem like I keep raising the Ve in those spots without awhole lot of sucess! Should have said lowering not raising.

[muncie21]

I have also put in larger injectors (42#). I am tuning VE right now and have noticed that I am running at -15 or so in decel. Seem like I keep raising the Ve in those spots without awhole lot of sucess!

You've got to reduce the min. inj. pulse. I'm running 42# Delcos in my C5 and that's what I had to do. I took 15% out from stock setting and now it controls like is should on decel and idle.

[ninobrn99]

ive noticed this also. mine is set to 1.277. Im running SVO 42# injectors. Would I multiply by 1.15 or .85 for 15%? How do you know or find what your Inj. Min. PW should be?

[muncie21]

ive noticed this also. mine is set to 1.277. Im running SVO 42# injectors. Would I multiply by 1.15 or .85 for 15%? How do you know or find what your Inj. Min. PW should be?

To get 15% reduction you multiply by .85. I would start at 5 or 10% though, and see how she responds.

[ninobrn99]

thanks.

[WS6FirebirdTA00]

i have 42#ers and the min pulse width didnt do jack, it doesnt effect idle on mine just decel

[EC_Tune]

i have 42#ers and the min pulse width didnt do jack, it doesnt effect idle on mine just decel

I'm guessing that you are well above Minimum PW at idle. Decel is where you will see the most benefit.

If you wish, here's a couple Histos I have for PW vs VE and Duty cycle vs VE.

EC

[WS6FirebirdTA00]

yeah i set the min pulse width to 0.8xx and decel did not change. The car still goes to about a 13.0:1 on decel. The pulse width goes no lower than a 1.8 mostly, although I have seen a few 1.7's

[sikhabib]

yeah i set the min pulse width to 0.8xx and decel did not change. The car still goes to about a 13.0:1 on decel. The pulse width goes no lower than a 1.8 mostly, although I have seen a few 1.7's

Im having extactly the same problem with the same min pulse of 1.8ms. I have my ve table into the teens and set min pulse width to 0.5ms and am still getting afr 13.xx decel. Ive turned on DFCO now until i can figure it out. Whats puzzling me is that i have stock injectors and stock injector tables so this shouldnt be happening. Im gonna put back in my stock tune tomorrow and see if i still have the problem

[WS6FirebirdTA00]

yeah its quite strange, i messed with the offset tables as well, that helped out some but not fully

[RedWS6 00]

I set min injector pluse to 1.2ms, default injector size at .8ms across the board. Still on decel I get betwen 11 AFR and 12.5 AFR. i have DFCO disabled at mo, my VE table is getting lower and still cant get a normal AFR on decel. I would like to see an answer to this too. I got 42lbr/hr@43psi injectors.

My OS is a 1BAR SD. It almost seems like its using another table when 20kpa or below, but i cant see it anywhere.

[muncie21]

What kind of injectors are you running, pintle or disk?