Minimum Injector Pulse Width

[curtbriggs]

B4003, can a change in the pulse width effect the AFR throughout the power band or only other then when in Power Enrichment mode or when in Decel fuel cutoff.

Thanks, Curt

[Tordne]

I'll be real interested in this as well. Well, I'm interested in anything to do with injectors really :)

You just inspired me to make a map of that B4003 table and look at data from a couple of runs.

[curtbriggs]

A friend, an experienced tuner, with an identical set of modifications, 2001 C5, reduced the pulse width 10% and his fuel mileage on a long Interstate trip went from 28 to 32. He uses HP Tuners with a wide band. Someone on the HP forum told him, in a PM, about this. Since the cam, mine has dropped to 28. My LTFT are -1 to 0. My cruise AFRs are in the high 14's.

[Tordne]

Interesting. I wonder if you reduced the B4003 table would you also reduce the B4004 table?

The B3701 table (Offset) also gets added for the battery voltage to determine the final commanded pulse width. I changed the offset table and that made a massive difference to my VE table.

I am kind of thinking of a reason why you wouldn't just drop the B4003 & B004 tables down to say 0.50. You are never going to be commanding that low except when DFCO kicks in. And that way you wouldn't be commanding a bigger pulse width than you perhaps need.

Does that sound reasonable?

Cheers,

[curtbriggs]

:wave: Anyone?????

[dfe1]

Hard to say. When my truck goes to DFCO, reported pulse width is .244 milliseconds. Smallest value in B4003 and B4004 is .759975 ms. The numbers on my C5 are similar.

[jfpilla]

The minimum logged for mine is .671. B4003-4 are 1.26. Not much help.

[Tordne]

Those minimum pulse widths are more than likely when DFCO becomes active and commands a pulse width of 0, which will then refer to the B4005 table and then add that pulse width.

I have experimented over the last couple of days with lowering both the B4003 & B4004 tables (down to 0.85) and at the same time 0'ing the B4005 table > 1ms.

Today I returned it all back to previous settings as I did not see any real difference.

[dfe1]

As if we weren't already confused enough, these are my results. I changed B4003 Min Pulse Width and B4004 Default Min Pulse Width as follows-
B4003 from .759875 to .683888
B4004 from .866258 to .653493
And also changed B4006 Small Pulse Width threshhold from 3.99 to 3.49.

Pulse width in DFCO changed from .244 ms to .214 ms.

I haven't driven it enough to determine if anything else has changed, but it doesn't appear that it has. Now I have to go back and change each one back to the original value to see what caused the change.

[Tordne]

There is also the Voltage Offset table. Could that explain anything with the variance?

[GMPX]

Some of the tuners out here with BIG injectors need to lower those to get reasonable AFR's at idle. I don't think it would improve economy, unless the result was the engine was running 16:1 AFR instead of 14.7:1.
Kicking in DFCO early is the best way to save fuel.

Cheers,
Ross

[dfe1]

I changed B4003 back to original values and DFCO pulse width went back to .244. So, for what it's worth, changing minimum pulse width values has an effect on pulse width when in DFCO. Still checking to see if it affects things anywhere else.