I have a 2002 trailblazer LS with a 4.2 I6. Truck ran perfect, but developed a rod knock.

So I purchaced the same year engine from a salvage yard with lower miles and installed it. Now it cranks but will not start.

I hooked up my EFILIVE tuning software and get these codes even immediatly after they are cleared.

-P1681-Control Module throttle position(tp) system
-P1635-5 Volt reference 1 circuit

Truck cranks but will not start, I smell fuel from the tail pipe, and both the CEL and Reduced engine power lights stay on.

Keep in mind, the truck had no lights or peoblems at all before I swapped the engine so I am not sure what could be the problem.

I swapped throttle bodies between the motors and still nothing.

Any help and ideas would be appreciated.

 

Double check all your connections and make sure you re-connected all your grounds. Its possible that something appears to be pluged in but did not click all the way. Physically check them.

Those are the only 2 codes showing???

 

was the replacement motor a complete drop in or did you swap over your sensors, injectors, plugs, coils etc?