Our TBI 454 runs an onboard diagnostics system that, combined with the engine management system and standard monitoring for gauges, requires the block, heads, intake, throttle body, and exhaust system (not to mention transmission and transfer case) to have a fair number of sensors. We decided that the best bet was to replace every single one rather than gamble that they might still work. In many cases we had no choice but to replace them since many of the old sensors had been broken. We also found that for every sensor there is also a specific plug on the wiring harness and more than a few of them were broken or cracked from aggressive removal. Unfortunately, a factory replacement wiring harness is no longer available, so we are running our current connectors, but plan on returning to Turbo City in the future to repair any wiring problems.