djm_e22

I have tunercat for my OBD1 lt1. I see the tables to change the boundaries. I'm having trouble on understanding how to set them up properly. Thanks for any help.

bobdec

Basically the PCM has 16 engine operating levels (BLM cells) 0-15. There are also 3 more for TPS=0 conditions that are are a little different. The PCm uses the blm data for each cell for two purposes..1st- to display whats happening and record the BLM data used for fueling in closed loop operation and 2- retrieve the BLM data and use it for fueling in open loop. Short term BLM's data is updated instantaniously and Long term BLM data is an ongong average if the ST BLM's. Here is a tutorial that may take a few readings to grasp. BLM cells are about 1/2 way down the page.. PCM Tutorial
In another post you said you are tuning for MAF-Open loop, in open loop BLM's are not updated, up-loading a PCM with code or powering it off will reset all BLM data to 128 and they will not change. Since all BLM data will be =128 in all cells there is no need to alter the cell boundaries for your tune. In closed loop I would log the car under normal running, then go through a log from start to stop and see what BLM cells you are using (verify cells by looking at MAP and RPM). With a CAM that has higher MAP and higher RPM at low engine ranges you will see that you probably never use the low BLM cells 0,1,2 & 3 and with high settings RPM maybe not 4,8,or 12. So your PCM would be running with 9-12 operating conditions not 16. In that case you have to alter the boundaries so all 16 cells are being used. Not to difficult once you get into it.

djm_e22

Think I understand the blm boundaries now. Thanks. Yes I am still debating on open loop or not depending if I can get my blm split to go away. I already did the throttle body mod with not much help. But I did notice the split go away as I got above 3000rpms and not yet in pe mode. So I'm thinking if the split cleans up in the higher rpms than I'm good to go for WOT. Just don't WOT below 3000. Which my stall is 3800 anyways. The worse the split got was I think 122/134 but after 3000rpms they were almost dead on. Correct me if I'm wrong on being good for the WOT after 3000rpms.

bobdec

122/134 indicates 5% lean one side and 5% rich on the other, can I assume you checked for exhaust leaks on the lean side, could you swap the O2 sensors left to right and see if BLM's stay the same (eliminates bad O2) . Could just be the air flow through you intake is not even due to mods. If the TB mod didn't help and your TPS voltage is good (.5-.7 volts) and IAC counts are near 40 and closed TPS timing is set at 30-32* for 400 through 1200 RPM. Rare, but could be a messed up injector. PCM correcting for one bank will add/pull fuel from the other causing imbalance. If everything is good you could try altering the 'individual cylinder fuel trim multiplier' table to balance the BLM's. That table only works for low end throttle, idle is column 2 and for TPS below 14% column 1 (off idle). Adding or lowering the setting X% for a cylinder alters the fueling that %. EG: Multiply setting by .95 to lean it out 5% or by 1.05 to richen the cyl 5%. Remember one cylinder can be causing the imbalance, but since the O2 reads the complete bank you can't tell which ons(s). Changing all 4 on one side may go to much one way, if so back of a couple cyls at a time to get it correct. Watch your knock counts, if it shows knock kicking in back off leaning that side, +/-5% should not cause any problems at low throttle, but just something to keep an eye on. As far as WOT, look at the BLM's for the cell just prior to going into PE mode, usually will be cell 15 or sometimes 14. The PCM remembers that BLM reading and then adds fuel on top of that reading from the PE tables. So if you are running rich or lean in BLM cell 15 it will stay that way through WOT. Therefore it's sort of the rule of thumb to make sure you are running good in cell 15 (or 14) before tuning WOT. If you BLM's are balanced and close to 128 in 15 then you s/b good to do WOT tuning from there.