Could having an intermittently active code 43 that is causing roughly 7* of retard cause split BLM's? Just got done with an engine swap, after about 20 minutes of idle time, I got a code 43. The only run time the car has after achieving closed loop is in Cell 16, haven't driven it yet....excuse me, because I am a bit green on the subject, but left BLM is under 128, like 119, right BLM above 128, somewhere near 149. Will this correct itself with drive time? Anything I should look for? Or should I just calm down, change the KS, reset the PCM, and drive it a bit? lol. Also running a madz tune if that factors in in any way. Thanks guys!

 

Easy thing first.. What engine year did you swap in..did you use the '95 knock sensor. Could be a resistance mismatch between PCM and sensor if not a '95 sensor. Here is some testing ref shbox.com. 4th Gen LT1 F-body Tech Articles . And here is a copy of the DTC troubleshooting from the service manual.. http://www.mifbody.com/DTCs/DTC%2043.jpg http://www.mifbody.com/DTCs/DTC%2043_2.jpg

I don't think the 43 has anything to do with split BLM's. You got a few things to look at.. Most common problem is exhaust leaks around headers, O2s . Then sometines after market TB's may require TPS adjustments to get TPS closed voltage between 0.45 to 0.75 volts AND IAC counts around 30-40 at idle. It's a balance act between the TB stop screw and sometimes rotating (oblong holes) the TPS to get both voltage and IAC correct. Descreened MAF can cause low end problems as it alters the engineered air flow design and really does not buy any performance.

 

Thanks Bob! Not by the car at the moment, but my IAC at idle was 31, my TPS voltage is right around .60~.65 at idle. I don't hear any audible exhaust leak, but I DO have a descreened MAF. Hmm. I'm going to change the knock sensor A.S.A.P, as my buddy is pretty sure he put silicone on the threads while helping me. I get infinite resistance sensor to ground...no good. Just was kinda hoping that if I fix the 43, it may help correct the block learn thing. And yes, it is an OBD1 sensor

 

I'd reset PCm (pull fuse, or battery ) that will set all BLM's to 128... There are a set of BLM's Long Term (LT) and Short Term (ST) for each BLM cell. You will be using BLM cell 16 during idle. If using freescan LT's are called BLM's and the ST's are called intergers. The PCM always uses LT BLM' in the fuel calculation to pick the injectors. The Lt BLM's are stored and remembered so they can be used during cold engine (open loop) startup. After closed loop they are updated constantly. So after a PCM reset and cold start LT's should stay at 128 till you enter closed loop (230 seconds). Then they should start updating using ST BLM feedback. The ST BLM's are just an exact reading of the AFR, they are not used for fuel calculation, BUT they feed/adjust the LT BLM's in order to correct fueling. So after running a while in closed loop and a LT BLM = 149 it says that bank is adding 149-128/128 = 16.4% fuel due to a lean mix and at that time the ST BLm for that bank s/b displaying the result of the fuel adjustment (adding 16.4%) and reading close to 128. Therefore always look at ST BLM's for actual engine running AFR and LT BLM's to see how much an engine is correcting for something wrong. At 16.4% lean and no air leaks !! you could have cylinder not firing or crossed wires. You could try playing with the TBS stop, lowering voltage (less blade opening) at first, lets more air go through IAC ports (IAC count goes up) and plenum in the intake manifold and distributes air more evenly. If it gets worse then try opening the blades, (lowers IAC) but at 31 IAC you can't go much lower. Does the TB IAC air port line up with the intake idle air plenum opening, sometimes there is a mismatch in size or alignment. TB should not have any idle air (IAC) channels feeding the intake main holes, all idle air should go through the plenum hole. If you get it running would be interesting to see ifproblem is idle only or is bad across all BLM cells.. Quite a few posts out there on split BLM's with bigger cams, but yous is stock ?.

 

Actually found and corrected the cause of the code 43, now I had a random code 36, and a 21.... The GM opti I pulled from the engine that I just pulled from my car that was problem free (put a new MSD cap and rotor, and new opti harness) and the TPS voltage is .62 closed and about 4.92 wot. Before my motor swap & tune, I actually had to look when I turned the key forward to be sure my SES light actually worked, because it NEVER came on. The only thing new to the car accessory wise since the swap is a used MSD 6al that I purchased from a member here. This afternoon the car briefly felt as if it turned off/immediately back on....also, the SES light has gone away after shutting the car off every time. I know I am all over the place with this post, but so are these codes, and I'm getting a bit flustered. I'm starting to suspect a problem with the MSD box, the way the codes are so random, I haven't eliminated it to check though as of yet. Aside from the brief stumble, the car actually seems to run great...oh yeah, running the LT4 hotcam with race gold 1.6rr's LT4 KM, shorty headers, 52mm holley. Thanks for the suggestion on the throttle blade angle stop and adjusting the TPS Bob, I have done that already in the past....that SHOULD be ok...afraid to make too many more adjustments until I can start making some kind of sense out of all this. Still kinda overwhelmed from the whole swap LOL