when the chip is removed from ECU does it hold the learned BLM's or is that lost? IOW's i swap out the 2732 in my 7747 without disconnecting the battery. just pop it out and put in a reburn. i was of opinion that if the battery is disconnected i lose the learned BLM's and reverts to the values in VE tables. would same apply on a swapped chip?

 

That's something I've always been curious about. On my 93 Caprice ($62, '6965) I don't think the ECM even applies closed loop BLMs to open loop, ever. I.e. I've never seen an open-loop BLM of anything other than 128. I think on mine, BLM data is stored for that ignition cycle only. And if it's saved between ignition cycles, it waits for closed-loop to apply the stored values.

 

I have been using Moates' GP1 in my 727 and each time I disconnect the negative battery cable. Is this actually necessary, or can I lift the lever, pop out the chip and reinstall without ever disconnecting the battery? Ed

 

i never disconnect battery. have removed chip possibly 50-100 times since i began tuning 7/2003. same ECU. my question is do i lose learned BLM's. reason i ask is car is going on dyno with chip swapping. possibly not an issue as will be in PE anyway.

 

The BLM data is stored in NV RAM and is retained even when the EPROM is swapped out. However, different masks treat the BLM values differently upon key on. A battery dance will reset the BLM valus to 128 at the next key on. The ECM 'knows' that it has lost power.

To first answer the thread originators question, the '7747 ($42 mask) has two BLM terms that are used as min/max's at key on. These are different terms then the min/max BLMs while running. The key on min/max terms are located at $2BB and $2BC. Setting them to 128 will ensure the BLM values are reset to 128 at key on.

The $8D mask (SD TPI stuff) only restores 2 of the 16 BLM values at key on. The other 14 BLM values are set to 128.

The '8746 ($61) resets all 16 BLM values to 128 at key on.

The '148 ($31) is like the '747 with new min/max BLM values used at key on.

The key on min/max BLM terms are such that if the BLM cell is within the min/max then it is left as is. If a BLM cell is greater then the max then it is set to the max. If it is less then the min then it is set to the min.

Also note that the BLM values are used even in cold engine open loop operation. Which while tuning can be troublesome.

RBob.

 

I just ran win aldl on my car for the first time yesterday and was wondering what a BLM was. I got a "blm enabled" flag and was wondering what that meant. While I'm at it I also got a MAF low voltage flag and I was wondering what could be the possible causes.

 

BLM enabled may be ECU went closed loop vs prior open loop? parameters have been met to allow?

 

BLM enabled is block learn mode enabled. In other words, closed loop mode - the ECM is using feedback from the O2 to control AFR.