Ok, so I've done some datalogging over the weekend and found that my lightly modded 91 GTA is running tad bit lean. It has a high flow TPI intake and headers/exhaust. Data log shows BLMs of 140 and up across the board, it did not drop below 140 at any time Sometimes it climbed to as high as 151. I compared it to a datalog I took in the middle of June and while I was running a little lean then also, my BLMs were in the 130-135 range. I'm guessing the difference would be ambient temperature. According to my notes the Data log in June was done on a 92* day while the log I took yesterday was done in ~60* weather. Am I on the right track? Would lower ambient temps (such as winter as opposed to summe) cause my BLMs to climb noticeably like that?

 

Yes, what PCM and mask? SD or MAF? I am guessing SD. You can add in a MAT sensor if you dont already have one to help counter this, or make a summer and winter tune.

Has anything else changed from then to now though? It something going bad on your fuel system, maybe pump dieing or filter clogged.

 

Thanks Dan. Yes, I'm running the 730 ECM with the 8D mask. Fuel system is in good shape. I checked fuel pressure and I'm getting 43.5 with the vacuum line disconnected which is normal. The fuel filter was also recently changed out from the old one. The only other change to the car was gearing. I moved from 3.23s to 3.42s. This wouldn't affect tuning right? Unless the VE tables would need to be modified because the engine is doing more work to get the car moving?

I was under the impression that the 730 TPI already had an MAT sensor which is the sensor under the plenum?

 

The change can also be due to changes in the composition of the fuel. Summer vs Winter blends.

RBob.

 

My 128 + or - BLM that I saw at 65 degF last week are now 140ish. Today I increased my tables and am running a cold weather .bin. I do however have IAT control but maybe need to consider my IAT/coolant bias tables???? I am currently at 96% % of CTS at 16 GmSec to 70.6% at 255 GmSec per sec. Would I not decrease the percentages further so that the bias favors the IAT?