Other than a possible ability to align commanded AFR with real world AFR through extensive WB tuning, are there any virtues I'm missing to running any PE when forcing full time open loop? My VE table is already all over the AFR range for drivabilty and performance of a big cam stroker. PE is mostly a way to work around stoich in a CL car. So without closed loop, or a constant AFR, any reasons why I shouldn't zero PE and just work my tune from the VE tables?
Thoughts?



The last post I found specific to the topic was in 2004, I'm hoping there has been some updates in data or new opinions.

 

If you've read through the stickies, I'm sure it's been explained in full. Once that's been done, it's just a waste of BW to rehash things.

I haven't had a closed loop chip in my hotrod, for ~5 years now. My truck is another matter, since it's happy at a constant 14.7 other then when in PE. THe GN on the other hand likes just about anything else OTHER then 14.7, so it's happy to be in open loop,

 

Everytime I visit the stickies the only thing I learn is that they need more maintanance than a 17 year old valley girl. It's not a "Rehash" when there are more new members joining daily and the core group of this board are constantly cycling. I'm looking for new thoughts and opinions, not old ones.

 

If it's daily driver and fuel economy is a concern, or if you go into the mountains (higher sustained throttle positions), then you might want to use PE mode.

Also, if you are running on the lean edge, and see a difference between 98 kPa 35% throttle, and 101 kPa 100% throttle, maybe you'd want to put a little more safety fuel in there.

If I were doing it, I'd probably use PE mainly for the fuel economy, and set up the tune for maybe ~5% PE when it's active. But that's only if it works well that way, don't force it.

 

What you said is true. New members join with new ideas and resolve some things that were left open. Another thing is that something may be misunderstood and solved later on. I find info in the stickies that is wrong a fair amount of time. In regular posts you find that sometimes they are resolved and sometimes left hanging.

I have been running open loop in one rig with the WBO2 on it. I still like to use PE (extra fuel) only when needed. It seems that the USA fuel is under going some changes and I am going back to closed loop because of it. I can't seem to keep the car in tune over the past few months. To keep it where I like it I would have to change the bin all of the time.

Keep in mind that spark and fuel change in PE and possibly some control stuff to when the PE bit is set. In the end, it probably doesn't matter how you tune by using just VE or VE with PE if it is more an offroad vehicle. If it was on-road I would tend to use both the VE and PE tables.

 

My 406 had a big cam and loose stall. It would reach 100kpa while not in PE. If I zero out the PE adder, then my part throttle will get additional enrichment. I like to keep PE and WOT s/a as adders for several reasons...

 

Part throttle would get additional enrichment without PE? Is that because you have negative values at lower RPMS?



I haven't seen a scan yet where I've hit 100kpa at anything but WOT or very nearly WOT which almost reserves the last column or two of the VE table for full throttle AFRs

 

If you go up in any sort of altitude, you'll see 95's at WOT, then higher, you'll see 90's, etc... The highest I've been in a car was up to about 58 kPa at WOT, if I recall correctly. Got sick as a dog too. Without enrichment there, you can cook things, but it's not the same heat level as stoich WOT at sea level. But, you'll be down on power, too (but with a monster engine, it won't be the same loss of power as the 1L engine I was in).

The VE correction at altitude gets pretty messy too, when using speed density. At 58 kPa AAP, we needed 15-25% more fuel, and the idle MAP was much lower, but the IAC needed to be more open (it's a messy combination of power requirements for accessories (constant), airflow through throttles at sonic pressure ratios and subsonic pressure ratios (<2:1), less pressure on the underside of the piston vs MAP, and slightly changing exhaust pressure - although I'm not convinced on the effects of that at such low loads and that flow there is not based on absolute pressure, only differential).

 

In some circumstances, you can max out your ve and still be lean with zero PE vs rpm added. Not everyone runs into this problem.
Also the stock code just wasn't designed to get 100% DC with zero PE.

 

The $8D also will only provide fuel for up to 100KPA even though the 1-Bar MAP sensor can go higher. These are referred to as the "normalization" equations in the $8D.

 

Are you considering disabling PE completly or just zeroing out the tables?

I'm trying the patched "super" aujp base bin on my new n/a motor, which is patched with a ve table up to 6400 rpm (which if I recall your cam specs, might suite you). I'm going to try to attempt disabling PE completly and just tune off the standard VE table.

In the past, I've zero'd out PE spark, but used PE fuel for upper RPM wot fueling.

The only problem I see is, can you have ve numbers over 100 in a cell? If you max out ve in any given cell and are still lean, will you then have to reduce your injector constant and resize all your table entries?

This is another one of those situations where I like the GM stuff for some things, but in terms of "fuel tables" I REALLY like the way fast does it. (injector pw or injector duty cycle vs rpm vs map).

-- Joe

 

The max the $8D can handle in a VE cell is 100 VE (0xFF in the table).

You like it because it is simple. With simplicity you lose tunability. That was this thread is about so I guess it fits. The reason that the PE table is there is for deviating from stoich. This thread is not about running stoich so I guess it fits. Also, comparing 21th Century hard was to 20th is apples and oranges. Since the old GM stuff can run an engine just as well as the new stuff I have to say it was pretty good coding & hardware for their first try back in the 80's. I am not bashing FAST stuff just showing that the GM stuff is good. It is more tunable and thus more complicated and requires more work to figure out.

 

GM's code has a million little routines to make a million parts of every day driving better, agreed. I just think the fuel logic was over complicated when it didn't have to be. There is no reason to have complex routines calculate VE (which is usually off anyway since airflow is calculated too) when they could have had a base PW, and fuel tables based on PW or DC. But thats just my opinion. You don't lose any tunability with that model, infact, you gain some. You've got your numbers right infront of you and don't need an ecm bench to see what your pw's are at any given RPM/load.

-- Joe

 

I've been without PE spark since hundreds of chips ago. I was only thinking about the fuel tables. One thing I didn't take into account is the fact that I lose resolution so to speak, with a correct voltage correction and injector constant 100VE might not be 100% Duty Cycle, I'm not going to look at the formulas but I'm pretty sure it takes PE fuel multiplier to reach 100% DC, something I need now but not when my injectors arrive, so I'm holding off on disabling it untill they get here.

 

When running open loop & no PE mode, the open loop AFR table(s) need to be adjusted. In the end, at WOT the commanded AFR should be the same whether you are in PE mode or open loop mode.

On hot cars I like running open loop. Biggest difference is that the power comes on smoother. The jump to hyperspace (going into PE mode) does not happen. The engine just keeps pulling.

RBob.

 

QUOTE: My VE table is already all over the AFR range for drivabilty and performance of a big cam stroker.

would it not be a good idea to get the underlying VE/BLM globally richer than 128 if running OL- PE disabled ? would this better insure that the resulting A/F in WOT be more accurrate or richer rather than leaner?

 

LOL, I like my "JUMP TO HYPERSPACE". Feels like the secondaries of a Q-Jet just opened up. I can really tell when I am using TOO much gas too!

 

with PE set to 50% my AE now blends with PE on WB log. used to be a defined seperation of AE timing out and PE arriving late. no defined SOP i can feel? maybe it is cause the tires are spinning as traction is compromised ?