Need some education on BLM. Car is a 1988 TransAm GTA. I recently swapped in a set of Bosch III 19# injectors on a completely rebuilt 305, with a 1993 LT1 cam and 1.6 rockers. Initial startup and BLM climbed to around 151-153 at idle. O2 sensor was switching from high voltage to low voltage. Vacuum was a steady 20 inches. Closed loop was set. During some trouble shooting, found a vacuum leak at the top of the runners. Pulled everything apart and resealed with new gaskets. Vacuum is now a steady 21 inches. BLM was still high, around 150. I adjusted the fuel pressure to 48 psi (vacuum line disconnected) and 38 psi ( vacuum line connected). BLM now reads 140-143. Integrator reads 127-130. So if the rich/lean flag is switching, the O2 sensor is switching and I have good vacuum and the integrator is within limits, why is the BLM out of limits? What else should I be checking? Only leak I can find is at the rear of the intake, but I dont think it would cause any problems except an oil leak.

 

I installed some Bosch III injectors on my L69 with LT1 cam. I had to change the Injector constant. After several trial and error attempts, I found that changing from the stock 19.11 Fire Size to 17.8 seemed to get my BLM's in order. The lower fire size told the ECM that the injectors were smaller, and therefore had to be held open longer. Don't know if this was the right way to do this, but it worked for me. I think you could increase FP and do the same thing????

 

Increasing the FP did help, it brought the BLM down to the 140's. As I mentioned, it is now set at 48 psi( vacuum line disconnected), not sure how much higher I could safely go without risking damaging the fuel pump ( we all know how much fun that is to replace!).

 

Yep, I think that was on my mind when I change the Fire Size. Not only a pump issue, but puts stress on the O-rings of the Fuel Rail. Don't need another fuel leak.