Will changing the VE map alter accel pump/transient fueling?

[Supercharged111]

I finally installed the wideband on my truck, havent' yet tuned. I'm noticing the low load sections are a little fat and so is PE, but it's not as bad as I was expecting. At any rate, I'm wondering if when I lean my low load cells to stoich will that net a lesser pump shot? The black box's lack of pump shot/transient fueling tables makes this suck if this is the case. Stock pump shots are usually a bit conservative anyway.

[Aloicious]

I finally installed the wideband on my truck, havent' yet tuned. I'm noticing the low load sections are a little fat and so is PE, but it's not as bad as I was expecting. At any rate, I'm wondering if when I lean my low load cells to stoich will that net a lesser pump shot? The black box's lack of pump shot/transient fueling tables makes this suck if this is the case. Stock pump shots are usually a bit conservative anyway.

I don't quite understand what you're asking here. the VE basically is used in calculating the airflow and hence the fueling. if you change the VE, it basically changes what the PCM thinks your airflow efficiency is and alters fuel accordingly (with other input like IAT, etc.) to be in sync with the calculated amount of O2 that 'should' be brought into the cylinder, the PCM alters the fueling by changing the pulse width of the injectors (again along with other fueling calculations as well).

I'm just not familliar with the term "pump shot". must be a regional dialect heh.

[joecar]

Changing the VE changes the looked up airmass which indirectly changes the commanded AFR for those operating conditions where the PCM uses OL and VE table...

in CL the PCM trims AFR to stoichiometric via oxygen sensor closed loop feedback;
in OL the PCM uses the richer of B3605 (CFOL), B3647 (COS CFOL), B3618 (PE; when enabled by B3616) to command the AFR;
at WOT the PCM enters OL and also applies any positive LTFT's (but only if they were positive);

above the rpm in B0120, the PCM use MAF to compute airmass (even if at WOT);
below B0120, the PCM uses either MAF (for steady conditions) or VE (for transient conditions) to compute airmass;

I believe by "pumpshot" you're refering to Power Enrichment (PE B3618, enabled by B3616).

If you want to reduce your commanded AFR, see if PE is enabling via B3616, and if so then adjust B3618 leaner where you want, or if PE is not enabling adjust B3605 or B3647 leaner where you want... leave the VE table alone unless you're using a wideband to correct it in OLSD.

[Chevy366]

I think he is talking about the transient fuel tables , they tend to act as if it is a "pump shot" when the accelerator is hit , briefly enriching fueling .
Never played with them but I think the tables were to suppose to end a lean tip in with FI , so I hear .

[swingtan]

It may be different in the US, but in AU the term "pump shot" would refer to the additional fuel added only when the throttle is moving "open". it's a direct term for the pump enrichment on a carby, so I'd say that it's being used here to describe the additional enrichment when the throttle blade is moving. Supercharged111 mentions all three conditions and also mentions the issues with limited "transient fueling" parameters in some controllers, his included.

As for the original question, I can only really speak about the E38 controller. In this case I'd say "not directly" as the transients appear to be greatly influenced by MAF airflow. So if you disable the MAF and go SD, you loose some control over the dynamics.

For the LS1 and COS3 etc. I "think" the OS calculates the values that it would normally get from the MAF and so the transients / dynamics are still tunable. In this case though, changing the VE would also effect the dynamics as the calculated airflow changes.

So, if you are not using a MAF, changing the VE "may" effect the transients or it may not. IF you still have the MAF enabled, then changing the VE may not a lot of effect on mixtures anyway. You'd need to go through an "Auto VE" cycle and then dial in the MAF. Either way, if you alter the air flow tables in the PCM and the transients use air flow, you are going to effect how the transients work.

Simon.

[Supercharged111]

It's not the AFR's I'm worried about, I can nail those with a proper auto VE tune. I'm concerned because, in my low load areas, I'm running 13.XX:1. When I crack the throttle from those low load areas when they run 14.7 (after an auto VE tune), I'm thinking that since the engine now thinks in SD it's moving less air it'll give a lesser "pump shot" and response may suffer. I have no control over the transient fueling with my POS black box and can't view many of the parameters Joecar mentioned. Since I can't see how the transient fueling is set up on this box, I can't see what might affect it indirectly.

[L31Sleeper]

Just do the 12200411 PCM swap. Just search E-bay motors for that part #
everything else you will find on these two web sites. I am also a member on
the pacific performance forum. All the info is there and mike at EFI Connection
has all the connectors at reasonable prices.

http://www.pacificp.com/forum/viewtopic.php?t=3240

www.eficonnection.com

P sout
-Justin