BPW, need some more info about it's limits etc - Third Generation F-Body Message Boards

JPrevost · 01-10-2002, 10:41 PM

What exactly is the BPW. I think it means base pulse width but what does that mean in terms of the ecm. If I have lots of fuel pressure and a very low PW does that limit my maximum BPW or does it make the fuel table less accurate (each point will be worth a larger pulse width percentage)?
I know I'm running really rich at idle but I don't know if I want to lower the BPW too far and if it'll have some ill effect on my top end performance potential.
I thought that the BPW is the min the injectors fire but what exactly is a BPW of 135 in the eprom. What is the actual time the injectors are open? Is the max pulse width the holding the injectors open?
Thanks in advance

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steve8586iroc · 01-11-2002, 08:33 PM

JV, I thought it meant band pulse width. Thats all I know other than it's measured in miliseconds. Maybe the percentages you are refuring to is the percentage of maximum duty cycle not base pulse width. I'm sure someone will straighten us out on this one.

Steve

mta227 · 01-11-2002, 11:02 PM

Quote:

Originally posted by JPrevost
What exactly is the BPW. I think it means base pulse width but what does that mean in terms of the ecm.

Base Pulse Width is the amount of time an injector must be opened for it to flow 1 gram of fuel.

The PCM uses this value as the factor in determining how long to open the injectors for each single inject (injector pulse width).

Duty cycle is expressed as a percentage, with 100% equating to the maximum amount of time the injector "can" remain open.

steve8586iroc · 01-12-2002, 02:25 PM

Sometimes I wonder what I'm doing on this board. I'm just glad someone knows what their doing. Sorry for the bumbling answer. Now we both know what bpw means.

Brent · 01-12-2002, 03:49 PM

The BPW JPrevost is talking about is the main fuel/displacement constant in the TBI software. Its kinda like the injector constant in the 165 and 730 only it's inverse. If you lower the BPW everything leans out, raise it and everything gets richer.

I can't remember if it is added or multiplied to the total fueling calculation. I wouldn't mess around with the BPW too much unless you have the VE idle cells down to 5 and its still rich. Just leave it be and adjust your VE tables.

JPrevost · 01-12-2002, 04:06 PM

Brent, I have my VE tables pretty low but because my fuel pressure is pretty high I still have a rich idle and low (sub 2000) cruising speed. I set my 2nd table all to 10's and I've been adjusting the main VE table.
You're right in that I'm wondering if the BPW is added or multiplied in the ecm. If it was multiplied then a low BPW would limit my abilities to tune on a higher hp motor. I'm hoping it's just added. I'll try some experiments with a few eproms and hopefully have an answer for the board.

mta227 · 01-12-2002, 07:25 PM

I have found that the most effective adjustment of idle mixture can be obtained by either changing the value at 0% EGR of "BPW VS. DESIRED EGR". or by just applying a factor to the "FUEL INJECTOR OFFSET VS. BATTERY VOLTAGE" table.

One reason that changing the offset is preferable is that on some port injection systems, there exists a constant that limits the "minimum" idle injector pulse (typically between 1.28 and .98 ms). This minimum value can present an obstacle when tuning idle mixture primarily by changing the volumetric efficiency fuel tables in attempts to accomodate increased injector size.

IOW, changing the offset can effectively override this minimum value, which is much easier than locating and changing the hysterisis pair responsible for setting these minimum values in the code.

Not sure how well this paradigm would apply to TBI, but it works well with port injection.