Dan Stewart

I noticed that all the "guides" suggest avoid entering PE when tuning via LTFT's, but they neglect to point out that anything above 4000rpm and 1/4 throttle and 15kPa activates PE.

Am I the only one that sets my TPS to 100% for enable when tuning LTFT's to avoid entering PE?

69LT1Bird

iTrader: (1)

DO NOT DISABLE PE!!!!!!!

Use the filter function in your software to ignore it. Lets see, 90% throttle, 5800 RPMS, No PE enrichment, hmmmm. What do you think will happen?

WeathermanShawn

iTrader: (1)

The whole purpose of tuning for negative LTFT's is to eliminate the additional fuel that would be unnecessarily added when you enter PE mode.

There is no inherent advantage to tuning LTFT's to ignore PE mode.

At the rpm's and TPS you mentioned, the cylinder wall temperatures encountered need the additional 'cooling' effect of fuel to prevent detonation and engine damage. Also the additonal energy relaeased by properly burning the additional fuel is what gives you power.

Did you have a specific tuning theory in mind to elimnate PE, or do you have an alternate method to add fuel under load?

..WeathermanShawn..

jimmyblue

iTrader: (11)

Way back before I had the wideband I worked by
setting EQ to 1.000 (PE and EQ vs ECT vs MAP)
and using a lower timing table, and used the NBs
real-time to set a high/low correction; add / subtract
big or little based on the O2 voltage range "bins" I
imagined might make sense (like +2% below 200mV,
+1% 200-400, -1% 600-800, -2% 800mV-1V. With
low enough timing (and decent KR protection / luck)
you can push into the higher MAP ranges without
hurt. Wouldn't try it with stock advance. And I
wouldn't try it with a statistics based (histogram)
approach, you would rather pick "anecdotal data"
out of an Excel file where you can criticize the
context, reject by eye stuff that is transitional
or noisy, etc.

A fair bit more work, but you get to avoid the
"garbage in, garbage out" problem of pulling data
into the distribution, that ought to have been
ignored (if you could express an elaborate enough
context filter, and said filter could deal with
history as well as present position, and so on).

Dan Stewart

Thanks Jimmy!

I knew I wasn't crazy. I always run much lower timing when doing so and set my knock sensitivity so that the computer goes nuts if I even fart.

I'll try using the EQ=1.000 approach as opposed to setting the TPS enable to 100% and see how that works.

That is until someone who has never done it chimes in and calls us both crazy.

It was bugging the heck out of me how guys were correctly mapping big cams with the pcm constantly entering PE whenever they got into the range where the cam starts to breath. After looking at my first 60 or so logs, I started to notice that the VE above about 3500rpm never looked any different than stock, yet the bottom half of the range looked just like a big cam should (dropping off into the abyss).

Since I started disabling PE, I started to finally get those much needed numbers in the upper range.

WeathermanShawn

iTrader: (1)

Hey Dan..

I am just curious what 'tune' are your running?

I.E. MAF or SD, closed or open loop?

I am curious about your working of the upper portions of the VE Table. If running MAF, CYLAIR will be your dominant airflow calculation.

Hey, maybe you are on to something. Can you expand on what you are attempting to do, and what tune are you running.

Thanks.

..WeathermanShawn..

gametech

iTrader: (1)

The "guides" that you refer to were written when most people didn't have widebands. Now that wideband 02's and tuning software are much cheaper, there is no legit reason to tune this way.

Dan Stewart

While tuning, I use a SD CL setup. Once I'm done, I switch it over to MAF CL.

To keep it simple here are my steps in a nutshell:

1. Disable MAF
2. Disable PE
3. Lower timing and raise knock sensitivity and attack
4. Adjust VE table via LTFT's
5. Re-enable MAF
6. Trim MAF using LTFT's
7. Re-enable PE
8. Return timing and knock sensitivity and attack to stock settings
9. Set EQ ratio using math for desired a/f at WOT (ie 14.6xxxx/12.7 = x)
10. Verify EQ ratio using mV feedback from NB
11. Decide if I want to trust mV from NB or trust my math....usually my math.
12. Add timing as needed (this and the final EQ ratio are adjusted on test and tune night at the strip.....dyno numbers are great, but I prefer lower ET's as the authority as to how fast the car really is).

Pretty much, this method helps utilizes the NB to see stoich and trim the VE table based on that.

The WOT fueling is pretty much based on math, for the sole fact that the NB is only good for measuring stoich.

And no, I don't even get close to 90% throttle while tuning VE. It isn't necessary and it's not very smart. I've never needed anything more than 50% throttle to hit the upper cells. The trick is to leave it in a gear low enough to hit the upper cells without having to increase the throttle. With enough practice you can hit a good majority of the cells. I usually log about an hour of drivetime each time, using stop and go traffic, hills, etc.

Yeah, a wideband is a great tool. Just not necessary to creating a safe and powerful tune. A wideband is more accurate and provides a means to completing the tuning much quicker. I'm not going to deny that. It just isn't "you better get one or you'll blow the car up" necessary. We did tune cars before WB's were affordable (yeah, I remember when a "decent" one was about $1500....I'm sure Jimmy does too).

69LT1Bird

iTrader: (1)

I have somewhat tried your theory. What I have seen is you are hitting cells you would "normally" not hit, the key would is normally. I could hit all kinds of cells if I left it in 2nd gear, slowly rolled into the throttle, brought the rpms up to say 4-5000 rpms 25 -50% throttle, hit lots of MAP ranges, that was all fine.

The thing is, when you actually drive the car, you never ever hit most of those cells. You can see while logging where your particular engine is designed to run, a curve will develop depending on the air flow needs of your setup. By artificially hitting cells just to say you did doesn't make your tune any better it just means you tuned areas you will never hit in real world driving.

As for not using a wideband or not being necessary, why would you not use the latest technology to tune your expensive engine if it was available? Doesn't make sense to me, just because you used to doesn't mean you should anymore. Does the factory skip the wideband? I don't think so.

WeathermanShawn

iTrader: (1)

Dan, that was a very intelligent and well though out summary. I appreciate how you laid it out in a very organized manner.

I personally have no problem tuning part-throttle using the narrowband O2's, providing they are functioning properly. I agree for those returning to closed-loop, your are going to have to utilize the narrowbands feedback in order to get the accurately tune the LTFT matrix.

I respectfully challenge using that method for that portion of the VE Table above 4000 rpm's. This has always been a hot area of debate. The experts insist that above 4000 rpm's, it is all MAF. Essentially they are implying that the VE Table is not even referenced at those rpm's. It may or may not be totally true.

Without making this thread response too long, I have used an interesting method lately to hit those areas of the VE Table that appear to be more MAF based. My tuning software has a calculated pid that allows a % VE using MAF g/s, IAT, MAP, RPM, and engine displacement.

It is surprising accurate, and does not require disabling PE. Like you, I have also used some 'simple' math and Excel software to display MAF g/s airflow and then compute the resulting DYNCYLAIR (SD) in g/s. You can easily then 'compute' those areas of the VE Table that you are referencing. While opposite of the current method to compute SD and then MAF, just something I have been experimenting with lately.

Thanks for explaining your tuning methodology. Now, I understand it.

..WeathermanShawn..

Frost

iTrader: (45)

It's not like it's some idea... Unless the MAF is failed and a DTC is set for it, above 4K is all MAF. I don't think that EFIL gives you the ability to modify steady state fueling or you would see it (and certainly use it) too. You need to set it to 0 or 100 to tune the MAF itself or you get VE blending down low.

On the left here is an entry labeled High RPM Disable. This is the switchover point. You can make the car run ALL MAF and even run SD without failing the MAF here...

WeathermanShawn

iTrader: (1)

Frost, thanks for the clarification.

I think the problem is that the VE/MAF blend at various rpm's and MAP is just not very well documented. I have never heard anyone say exactly the precise amount (%) how much VE influences idle and lower rpm, and how it blends as it reaches the 4000 rpm threshold.

I realize in the software you can change the thresholds to your own preference. And, I agree from practical experience that below 2000 rpm's the influence of the VE Table in transient fueling appears to play a greater role.

I am just asking, "does anyone really know in exact amounts how they blend under 'stock' parameters"?

Frost, I have done the same approach you take on working on the <2000 rpm VE Table, and enabling the MAF threshold to a lower threshold. But, I have heard many arguments that insist on a perfect VE Table to max rpm.

Do you agree that are a lot of confusion of VE/MAF role tuning, even to this day?

Thanks.

..WeathermanShawn..

Frost

iTrader: (45)

Absolutely!

If you are tinkering and wish to see influence, put the car "on the MAF" 100% and tune it. Now go back, load a stock VE and move the MAF's chop point to 4K and watch what happens...

The VE needs to be tuned at least at WOT and beneath 4K everywhere (for not only transitional fueling down low but protection at WOT in case of MAF failure in the future), but doing more is certainly being more thorough.

jimmyblue

iTrader: (11)

One thing a proper, high-RPM VE table gives you
is decent transient throttle behavior. Like say one
of you M6 boys is rolling around the road course
at 4200RPM and decides to mat it coming out of
a turn. Steady state MAF, all well and good but
if it's "covering up" a too-lean speed density base,
that tip-in exposes a lean hole (unsteady-MAP
leaves MAF mode for a period) and you step into
a few seconds' worth of KR.

In fact I used to look directly at this, do throttle
punches and look at how the narrowbands break -
break high, speed density is richer than MAF;
break low, leaner. I would bump up VE cells until
tip-in produced no lean dip, when I was working
that way.