Any upper or lower block learn limits?

[Gary Wells]

What lower & upper limits are considered normal for TB's?
Variation or difference when on or off pedal?

 

[turbo nasty]

128 +/- 10

 

[we4Mateo]

How far from 128 can the counts go? I've often wondered this too so I knew when it was pegged.

 

[Mike Licht]

My preference is to have the car run between 120 and 128, limits depend on the chip and how far they are opened up 105 on the bottom and 150 or 160 on the top are common limits

 

[Mike Licht]

As long as we are talking about block learn, I get lots of phone calls from people that say "my car is way to rich or lean" "I can smell it" The block learn is an indication of how far the ECU had had to learn (fuel trim) to get to the target programmed into the chip. So if your car is at 120, 128 or 135 it will run the same air fuel ratio if things are functioning properly. driveabiltity suffers when we have big trim changes as we change from block to block for instance if we have a 140BLM at idle and a 120BLM block just off idle we may get a stumble as we transition from one to the other.

 

[we4Mateo]

As long as we are talking about block learn, I get lots of phone calls from people that say "my car is way to rich or lean" "I can smell it" The block learn is an indication of how far the ECU had had to learn (fuel trim) to get to the target programmed into the chip. So if your car is at 120, 128 or 135 it will run the same air fuel ratio if things are functioning properly. driveabiltity suffers when we have big trim changes as we change from block to block for instance if we have a 140BLM at idle and a 120BLM block just off idle we may get a stumble as we transition from one to the other.

Good stuff. Why the preference for 120-128? Keep it taking away fuel a little rather than adding so it's there if you need it?

 

[Mike Licht]

it just where we seem to get the best driveability

 

[Gary Wells]

Many thanks, everybody.

 

[Gary Wells]

Any relationship between high or low BLM's & vacuum leaksP

 

[psycho6cyl]

http://www.vortexbuicks-etc.com/

 

[we4Mateo]

Any relationship between high or low BLM's & vacuum leaksP

Vacuum leaks cause high BL's due to unmetered air getting into the system and the ecm needing to add fuel to compensate. Usually only an issue at idle.

 

[750H.P.V6]

While we're on the topic of block learn values I've mentioned this before but everyone tends to want to rehash the same info over and over. Depending on the injector constant programmed into the chip itself by the person who did the calibration the BLM #'s can be high or low. If your MAF reads high or low this will have an effect on the BLM. If your fuel pressure is higher or lower than roughly 43 psi this will have an effect on your BLM.

Dependent on where you live lets say for sake of argument Death Valley CA vs Santa Fe NM will have an effect on your BLM. The adjustability in the programming was put there for a reason, to compensate for different conditions that may occur depending on where the vehicle is operated. 128 is the centerline value, most chips have a minimum of 90 and a maximum of 160. If your BLM's are not at either 90 or 160 the car will run fine.

Neal

 

[GNRick]

If your BLM's are not at either 90 or 160 the car will run fine.

Neal

The car may run fine but wouldn't gas mileage suffer if you are adding fuel needlessly?

 

[we4Mateo]

The car may run fine but wouldn't gas mileage suffer if you are adding fuel needlessly?

That's the point. The ECM doesn't do anything needlessly. It does what it's programmed to do based upon the input data it receives. We manipulate the data to get what we want, but the ECM will always try to run stoich based upon what it sees. The BL is only an indicator of what the ecm has to do to achieve it's goal of stoich AFR's.

Basically, if everything is working right, gas mileage should be the same regardless of BL as long as it has not hit the upper or lower limit of adjustment; ie: 90 or 160.

 

[Jerryl]

BL is long term adjustment, INT is short term adjustment and ECM will adjust BL based on INT value. For example . .
INT is 138, adding fuel. The ECM knows this and will adjust BL, to make the INT happy, AKA the 128 value, for a specific BL cell which corresponds to a specific operating range. As the BL adusts, the INT will get back closer to 128. Once the INT is back at 128, BL will stay and hold.

So, as long as the BL adjustment is not out of range, the ECM can still control the fuel, and the car will not really run much, if any, different. INT value is what you feel, BL is how the car behaves.

Now, if the BL is maxed on either side, the INT will adjust and since this is not stored, the quality of the feel diminishes. This is when there is an issue as the ECM no longer has control.

Fuel mix, ambient temp, injector offset, baro, etc. all affect BL. This is why the adjustment is needed by the ECM, because some of the variables, we have no control over.

 

[Mike Licht]

the exception to this is for instance when you have a vacuum leak which drives the BL to the limit or the fan is blowing are across the MAF sensor which gives a false reading. If everything is operation properly car should run the same regardless of BL

 

[Jerryl]

the exception to this is for instance when you have a vacuum leak which drives the BL to the limit or the fan is blowing are across the MAF sensor which gives a false reading. If everything is operation properly car should run the same regardless of BL

Very True. But that typically only applies to the idle cell. (True?)

 

[Mike Licht]

yes, part throttle maybe if it gets to the limit

 

[GNRick]

That's the point. The ECM doesn't do anything needlessly. It does what it's programmed to do based upon the input data it receives. We manipulate the data to get what we want, but the ECM will always try to run stoich based upon what it sees. The BL is only an indicator of what the ecm has to do to achieve it's goal of stoich AFR's.

Basically, if everything is working right, gas mileage should be the same regardless of BL as long as it has not hit the upper or lower limit of adjustment; ie: 90 or 160.

So if there is a vacuum leak and things are not working right would gas mileage suffer?

 

[Mike Licht]

Maybe, need to see a log, it would not be common