Originally Posted by tylerwerrin
I had put some #30 accel fuel injectors into my 1996 impala LT1. It ran a bit rich, but it seemed OK. However, today i was sputtering all over the place, actually stalling out. The car started right back up, but as i stepped on the gas, i'd eventually start chugging and stall out again.
Is this due to the #30 injectors? I put them in because the #24 stock injectors i had were fouled. I never tuned to PCM to work with the #30's, i just assumed the PCM would adjust.
What do you think?
Bad assumption! That's a 25 percent increase in fuel flow with no other changes and it's everywhere from idle to WOT, either the engine cold or hot. The computer when new has about a 10% adjustment range. A 1996 uses Manifold Absolute Pressure (MAP) instead of directly measuring air flow as in Mass Air Flow (MAF) systems. The MAP system is a lot less capable of making adjustments to fuel quantity as it computes air flow rather than measures it. Since air flow hasn't changed, and the sensors that read it haven't changed their outputs, it has no real good way of knowing about the 25 percent more fuel till it gets into closed loop operation with the O2 sensors switched on. At that point they just see rich and try to dial the switched on time sequence back for the injectors. But with 25 percent excess flow and 10% authority to change that flow on their best day, that leaves the engine 15% too rich.
There's two solutions, back to 24 pound injectors or a pre-processor put onto the ODB II computer. Lots of web sites, just Google the question.