19doug90

So this is really a continued thread from the multi paged other threads ive read on this.

first of all i dont have cats so thats not an issue.

I dont like the idea of running in open loop because no matter how bang on the tune is you change elevation even a little or even differences in the weather and your tune isnt going to be exact. I would like for my computer to be able to compensate at least a little bit based on what the sensors are reading.

Now the issues ive read with closed loop and agressive cams where ive read multiple posts of people saying the BLM's are at 128 while the WB is reading 15-16:1 which is downright scary.

im trying to get a better understanding of why i should be tuning in open loop where i get no adjustment, and why closed loop cant be made to work, or isnt worth using.

Grim Reaper

Actually, closed loop works quite often. People use open loop for a variety reasons INCLUDING developing your "base tune" and then invoking Closed Loop once they built their Open Loop VE Fuel Map. But, some times, your setup is just so aggressive (especially with SD) that the car just doesn't run as well in closed loop as open loop. This also happens when you end up using an overall AF ratio other than 14.7:1.

So, take this approach - develope your base tune in open loop where it runs "the best" using a WB O2 sensor as your guide. Don't worry about 128/128 with the cars Narrow Band O2 sensor - people do that when they DO NOT have a proper Wide Band O2 sensor.

Once you develop you "Open Loop" VE Fuel Map, try running in Closed Loop. If it runs well in Closed Loop, use it. If it doesn't run well in Closed Loop, keep it in Open Loop.

19doug90

okay little bit of a random question, but in theory the % change a/f in open loop table should function very similarly to what PE does, but im guessing PE would override the change in a/f for the pe area

i also dont fully understand how PE and the VE table get along. Why bother having a table that changes the values in the VE table by a given percentage when you could just edit the VE table to give you that a/f? or is that simply because in closed loop its shooting for a tarfet afr and if you didnt run the PE table it would think you were way off and pull all the fuel.

90c350

The reason for example of the Pe table is because under certain driving conditions, I.E going up a hill you can hit 80/90% Ve at say 2000 rpm. All the while not being into the throttle hard. Therefore you would only need a ve% that would give you around 14.1 AFR. But if you hammer on the throttle you would need more fuel ex- 12.5.1. Just like an accelerator pump shot. So you need to tables to keep everything happy. If your 80/100% Ve always gave you a 12.5.1 AFR you would not like how the vehicle drives and would also be using alot more fuel etc. I hope that this helps a little bit??

Grim Reaper

Also when GM designed these bins, they also were going to invoke "Highway Mode/Lean Mode" but subsequently did not (believed because of the EPA and NOx issues).

The HM tables were the opposite and leaned out the AF ratio. Basically these tables were "adders/subtracters" from the VE table and the trick (espeically if you invoke HM) is to make sure your transition between the HM, normal and PE modes are done properly.

And the example of placing a load while going up a hill versus putting the pedal to the metal for passing is correct. Ditto for passing when going "down hill", your MAP value may be lower than normal and the ECMs needs to know the pedal is on the floor board.

If you lived in a "flat area" of the country, you could use just one table. But if you live (or travel) in a mountainous area or use HM, using separate tables make tuning easier IMO.

Street Lethal

iTrader: (16)

But your making a mountain out of a mole hill though here. In Open Loop, the ECU will read all sensor information, confirm programming to determine the desired A/F ratio, calculate the required injector PW, then send that PW to the fuel injectors hoping for the best (in OL). True, it never really knows if the desired A/F ratio was acheived or not, but this is why we have AFR gauges, and substantial elevation changes are simply a tune away. I personally don't feel changes in weather are that detrimental though....

Slewis

If I'm not mistaken BARO gets updated somewhere in the part-to-full throttle accel(don't know how it's calculated though), and is what is used for current ambient press changes, compensating for the weather and altitude changes while driving. This is used wether it's in open or closed loop, MAF or SD.

RBob

iTrader: (1)

Please note that elevation changes have little affect on GM EFI systems. There is more change due to chamber temperature and humidity.

Of which temperature can be compensated for. Not perfect, but darn near close. And baro is also compensated for. Which leaves humidity.

As for elevation changes (or barometric pressure changes), may want to search or a post or two where the affect is explained. It probably isn't what you are thinking.

RBob.

19doug90

ill try searching

my logic was if i tune it in edmonton where were at something stupid like 3500 feet, the air is less dense.

If i were to then race the car at sea-level where the air is much denser, there would be a lot more oxygen in the air and would require more fuel, and possibly a slight timing adjustment

Grim Reaper

I think it depends on how big the mountains are and how much the variation you experience. Where I live, I can go from sea level to almost 6,000 feet in a couple of hours driving on a route I frequent. Especially with using HM, I found it easier to just use all the tables. One table just didn't work for me.

Grim Reaper

When you tune for Edmonton, you won't even be able to tune the upper kpa regions of your tables regardless of which method you use. In WOT, you'll never hit higher than the mid 80s kpa.

The only time you will be able to tune the highest kpa regions is when you go to sea level. And to tune those, you'll need to leave the P/E table "constant" from when you left Edmonton or you'll be mixing "apple with oranges". This is why guys prefer to tune with just the main tables and forget the P/E tables all together. With just one table, you make a "generalization" that anything over 75 kpa is WOT and those KPAs relate to a particular elevation.

This only becomes a problem at EXTREME elevations (say 6,000+ ft) which is in the upper 60 kpa. This is also in the cruising range in lower elevations. Then you MUST use multiple tables. But if you never (or seldom) think that you'll be at that extreme elevation (and most won't). Then one table will work. I have and do travel at those high elevations, and that is how I discovered this.