1993 Buick Park Ave. 3.8L. Warning lights: service engine soon, inflatable restraint. Codes: throttle position sensor.
Question = the engine got hot in my 1993 Buick Park Ave.w/3.8L V-6 and spun the crank everything else worked great! so i bought a used engine that is low mileage and runs excellent and had my mechanic remove the old engine and install the new one and ever since he did the in dash warning gauges (oil pressure,temperature and charging) are inoperable. Ive already checked Fuses,checked wiring visually,cant find any problem HELP ME!!! also leaks oil really bad w/oil fill cap installed no leak without cap.

Answer: He either forgot to hook something up, like a ground wire. Or the used engine you bought is not exactly the same as what you had. Different sensors, even if plugged in, sometimes won't work on different vehicles. If your car had been oil pressure gauge in the used engine had oil pressure light, then those sensors would be different. I same goes for the temperature sensor. Depending on the year the engine the internal wiring of the alternator may not match the car.

As for the oil leak, when you have the oil fill cap on, the engine is allowed to build crankcase pressure and oil will leak out of what ever gasket is bad. With the cap off, you are relieving that pressure and keeping the oil from leaking. Check to make sure the PCV valve is installed. If it is not the engine will suck oil and burn it very quickly. I would not drive around without the oil fill cap installed, as that can cause drive ability issues and eventually oil will come out of the fill hole which can catch fire on a hot engine.