PE/6E + DFCO questions

[dyeager535]

I tried to search, but of course PE and 6E are too short. :(

My base bin is APYP. Still narrowband, so essentially guessing on fueling here, but at least watching the O2 sensor to see that it stays rich. My question is, if the displacement of the motor is the same (well, +5 CID), and larger injectors are taken into account in the tune, why would huge differences in the PE vs. RPM table be needed?

In the stock APYP table, the addition of fuel seems to make little to no sense...they add fuel, pull fuel, then add fuel again in PE vs. RPM. I can understand not needing as much fuel as the engine load decreases (RPM increases) but I would think that taking fuel out in the middle of the RPM band would have resulted in a nasty flat spot on a stock motor. From my tuning, adding fuel and smoothing the table out (add fuel early, taking some out as RPM's increase) has made a marked difference. But based on the size of the motor, and what I call moderate modifications (TPI w/mild cam, Vortec heads, long tube headers) it just seems to want a lot more fuel. As a for instance, on thirdgen I found reference to some guys who needed 70% increases in PE going to a 383. Those motors likely make a LOT more power than mine, with vastly different components, but again based solely on displacement differences, a 70% increase still seems massive. These guys were saying on their motors 12-15% increase in PE was worth 1 "point" in AFR.

Also, DFCO doesn't seem to be "working". If DFCO is working, lifting throttle at speed (while meeting the various parameters necessary for enable of course) should show the O2 going lean and staying lean, correct? Mine keeps showing O2 cross counts and I'm well within the enable parameters. Perhaps I'm misunderstanding DFCO, but I know in more modern vehicles, the injectors are completely shut down. The places I drive (tons of uphill and downhill) shutting off the injectors on downhill would net me a substantial economy increase. I made all sorts of changes to the bin in relation to DFCO, and still couldn't make the O2 act like I thought it should. I believe in the datastream I have DFCO actually ends up being shown as Yes/No, and it never shows yes.

Don't have a log currently, was making the changes on the fly.

[EagleMark]

What your describing for PE is about right. PE usually has a drop and no return, it's a RPM limit so power drops and you shift or auto trans shifts. It was never designed to give real 12.5 to 1 AFR for power, just a little boost. Some have such a big delay it never comes on! Well after 60 seconds probably to cool the Cat... Some will go Open Loop and you can see O2 sensor readings steady. But this does not happen with delay.

PE AFR is a balance to get right. With smaller injectors and pressure the increase can be large when Main VE is pushing 90-95%. But if you have bigger injectors and higher pressure with Main VE under 80% can be small.

DFCO and Decel fuel Enleanment are 2 different things. One cuts fuel and one Enleans. The window is very small. My 98 Vortec truck on freeway will enter DFCO after a long delay and Wide Band goes max lean between 1900 RPM to about 1100 RPM when it starts fueling again as long as I never touch throttle. If I do it's over! These are all sensitive to TPS%.

Wish I was more familar with $6E to give more precise answers? One thing I have learned with Tuning Software of all kinds is the paremeters you need are not always there!

[dyeager535]

I'm beginning to think MAF just straight sucks (at least early like this). I know far brighter than I have visited that topic, but it seems so little is interrelated compared to the MAP setups. You get VE right in MAP and other stuff appears to fall into place (with some tweaking here and there of course) but in MAF, you can get 128's across the board at cruise, as soon as you put the pedal down driveability disappears, or it doesn't like to start when the coolant temp is different, etc. And it's not just little tweaks. I'm up over 20% in PE just to make a noticeable difference.

I also think I may need to start out with a bin/mask that hasn't been so extensively mapped out, to see if maybe some of the issues aren't related to that. Import the stuff I know works now, and see what happens when some of the variables are removed.

[RobertISaar]

the early MAF systems were quite tempermental like that...