VetNutJim

This applies to CLOSED LOOP NON PE operation ONLY.

Ok, I've been burning chips long enough to be dangerous to my engine and to society but I'm NOT an expert.

After learning about BLM's between 108 and 160 I've come to have a very basic question.

I'll make a couple of dumb statements before asking the question.

The GM EFI system is designed to 'recognize' and 'learn' what AF ratio the engine is experiencing.
It is a 'closed loop' system with the primary feedback element being the 02 sensor and several secondary inputs such as air temp, engine temp, etc.

The PRIMARY feedback device (02) has a very limited range of operation. However the system was designed to control the AF ratio (in CL) with this device.

Here's my question:
Since the control system has the ability to 'learn' and store variables to control the AF ratio within a preset range of values (108 to 160 BLM),
why does it matter if my BLM's are at 110 or 150 or any range in between the design limits of the system (108-160)?

Dumb statement:
It appears the ECM will 'learn' what correction factors it needs to apply to what it is measuring to bring the AF ratios to the Stochiometric value as set in the EPROM constants table.

Doesn't it do this by storing the BLM values into RAM so they can be referenced in the future as the engine is operated in similar conditions as in the past?

Here's my same question again:

If I don't change the design (or 'Volumetric Efficiency) of the engine so far from stock that the ECM cant' compensate and modify the 'learned' values why do I need to adjust anything in the fuel tables?

I can see the need to 'retune' if anything is changed that affects airflow or fuelflow. Maybe even if I want to change the timing.

But if I scan my 'stock' engine and find the BLM's at 110 to 112 or maybe at 140 or 150 [b]why do I need to even try and change them?[b]

1) Won't my ECM 'learn' what it needs and automatically apply the corrections?
2 The ECM can apply corrections quickly so is my engine losing performance by not having the INT & BLM values sitting right on 128?
3) Will my engine run 'better' if I make the adjustments to drive BLMs closer to 128 right now?

It seems that even on highly modified engines that once you get it 'in the ballpark' the ECM could handle the fuel calculations from there.

:hail: To you experts that can answer these questions and thanks in advance for taking time to explain all this in more intimate detail.

Jekyll & Hyde

Good questions, I await the experts reply.

TRAXION

1) Whenever in Open Loop or Closed Loop but with learning disabled the BLMs are not being applied. Thus, if you normally have 110BLMs at idle then when you first start the car (Open Loop) the car will be washing the cylinder walls with fuel. That means extra wear since the extra fuel will be washing the oil off the walls.

2) I don't think the learning and BLMs are perfect. In other words - I can be in a car with bad fueling curves but where the ECM has learned to compensate. The car feels OK. However, when the fuel curves are tuned it just feels smoother, more responsive, less sluggish, etc. Something isn't perfect about how the BLMs operate. Maybe it's due to the cells? Not sure.

3) Tuning part throttle will give you a general idea for how the fueling curve looks and allow you to determine what the higher load areas are going to be like. Tuning those areas will keep you safer because you don't want the car to have to learn those areas and go through detonation to have to learn it.

Tim

Grumpy

It will run just fine, at other then 128s, as far as the ecm, and code are concerned. Some of the art in doing calibrations is how it feels to the human end of the equation, and keeping the engine happy.

BLs are only updated at a specific interval, so there is a lag from what's sensed to when it's applied. And a delay from when the gases leave the chamber until sensed by the O2 sensor.

If you were to tune *everything* with the BL geared to read 122 you'd probably not notice a difference, between that and 128, 128 is just the center of 256.

Getting close to 128s just means less other stuff will be off. Get close to 128s, and move on, IMO.

Ballparks vary by player size.
Doc, made me add that.......

Possible, bad/neg vib/bad juju, comment, about starting and 110 BLs edited.

RednGold86Z

iTrader: (1)

Our system has block learn also, and it's done on a slower updating portion of the software, which means that if say a low MAP block is low and a high MAP block is high, a transient can cause a lean backfire or misfire since the update occured after the transition. I think GMs block learns don't update very fast either and could suffer the same symptom.

Another thing, is if your fuel map requires say 90% at one end of the block and 110% at the other, then that block will never be totally correct, and that could be felt if it happened to be at 90 when you needed it at 110%. You're not doing a full emissions drive cycle, so I won't bore you with the emissions effects.

It may also surge if you enter a block that is not learned correctly.

It may also be a nuescance if you frequently disconnect the battery to have it drive terrible until it learns.

And then there's PE, which I know you said to disregard, but that gets affected and is most critical to performance driving. Now if someone were to edit the code (hint hint) to allow BLFs of less than 128 used in PE and open loop warm up, then you could have a self calibrating system (and just rig up a 9 volt battery to a cigarette lighter plug and then disconnecting the battery won't be as much of a problem (unless welding)).

BJM

Not sure about your ECM but in a GN the BLM is always used. If your learned values are really far from 128 everything is fine even in open loop, it just uses the values as is and doesn't try to learn until nearly warmed up.

The problem is when resetting the computer, until it has relearned, you are stuck with 128s across the board which will be lean or rich depending on your final learned values. Before learning to do my own PROMs I had my low cells on one chip normally at 140-145 which meant that after resetting the ECM I had to run very lean until learning took place, it was pretty bad.

The other comment about one end of the cell being different is also true, this would normally be noticeable when adjacent cells are always at quite different values. The MAF calibration is wrong somewhere in between those cells ranges.

I have fixed my MAF tables to the point that resetting the ECM has nearly no effect which is nice.

The other issue is the Integrator which is also trimming things, the BLMs learn slowly on purpose. They learn in order to have the INT bounce around the 128 value. If its mean value moves off 128 the BLM adjusts to fix that. The integrator is cycling up to several times per second and the control loop is altered based on look up tables for how fast the engine should be responding (in seconds) to a fueling change rich or lean.