Injector sizing through pulsewidth only?

Reply Subscribe

Thread Tools

Search this Thread

Dec 11, 2007 | 10:42 AM

xssive

Thread Starter

TECH Addict

iTrader: (123)

Joined: Nov 2001

Posts: 2,256

Likes: 2

From: Austin, TX

Injector sizing through pulsewidth only?

This isn't on a stock pcm, but an aftermarket mefi4 based system. Its an MSD mefi4 system for an ls2. They use the UMI/Arizona Speed InGenius tuning software, but there isnt a table for changing injector flow rates. They are telling me it all handled through pulsewidth modification.

So, does that sound reasonable? Im guessing just decreasing the pulsewidth with increased injector sizing using a wideband to tune in the afr?

Dec 11, 2007 | 10:44 AM

RZRSEDGE

TECH Enthusiast

iTrader: (21)

Joined: Jul 2006

Posts: 609

Likes: 0

From: Tellico Plains, TN

Sounds like a major PIA!

Dec 11, 2007 | 05:22 PM

slow

TECH Senior Member

iTrader: (7)

Joined: Dec 2001

Posts: 6,150

Likes: 7

From: Orlando

sounds like older jtec based dodge vehicles, the fuel table is pulsewidth based on map and rpm.

Ryan

Dec 11, 2007 | 05:33 PM

xssive

Thread Starter

TECH Addict

iTrader: (123)

Joined: Nov 2001

Posts: 2,256

Likes: 2

From: Austin, TX

Yeah its totally pulsewidth based on map / rpm like you said. It's afr controlled closed loop tuning once you dial in the fuel tables to around 5% of your target. It idles around 4 cells in the table which you can inc/dec in real time with a single click. Pretty cool actually

Dec 11, 2007 | 07:38 PM

gametech

TECH Veteran

iTrader: (1)

Joined: Sep 2004

Posts: 4,904

Likes: 906

From: Stockbridge GA

Quote:

Originally Posted by xssive

That is VERY common with aftermarket ECUs. Why should they bother incorporating VE and IFR into the calculations when that processing power could do something else? Basically everything that a stock computer does to calculate pulsewidth is unnecessary if you just start with PW. It can be a bit more challenging to build an initial table, however, unless the tuning software provides some base calculator functions to help.

Dec 11, 2007 | 07:52 PM

2002_Z28_Six_Speed

TECH Veteran

iTrader: (19)

Joined: Aug 2005

Posts: 4,538

Likes: 1

From: Wash, DC

Quote:

Originally Posted by gametech

So true! Sounds like you could use a spreadsheet to get the inital PW table.

I was thinking about it and it almost seems like you could bypass alot of things like experimentally finding the true IFR, small pulse adjust, and all that jazz.

BUT. This setup would make it tons of work if you changed the injectors. You would have to do it all over again!

Dec 11, 2007 | 08:18 PM

gametech

TECH Veteran

iTrader: (1)

Joined: Sep 2004

Posts: 4,904

Likes: 906

From: Stockbridge GA

Actually, when changing injectors you apply the appropriate percentage change to the entire PW table to get you pretty close. Then you are left with all of the usual minor tweaks to accomodate the REAL differences in IFR.