I have an 87 Blazer with a fuel injected 350 in it. The motor isn't stock but everything should work well with the stock computer including the cam. Sometimes the beast runs like a dream and other times it seems to have no power. The computer gives me both an EST (Electronic Spark Timing) and a lean exhaust code. I'm assuming the lean exhaust is due to the dual exhaust but I cant figure out the EST. Any suggestions?? I appreciate any input!!