I installed a 92 engine in my 90 model Q45. the engine started and sounded fine it just would not stay cranked with out giviing it constant gas and there was a weird noise comming from the air intake (mass air flow meter housing). It sounded almost like a car sounds that needs a muffler job eccept instead of hearing the noise from the tail pipes it was comming from the air intake chamber. My machanic said I needed a knew mass air flow sensor. I was told that the 92 engine would not install in my 90 car with out changing the electrical wiring from my old engine. I do not know if this true to this day and if that's the reason why I am hearing the weird noise comming from the air intake (a boubly sound if that makes any since) or if I really need a mass air flow meter. I would like a second opinion from someone who knows before I go out and spend hundreds of dollars on a sensor simply on a mechanics guess tommorow.

MAF should be compatible from 90-96. I'd suspect an air leak - someone else will answer soon, but from what I've heard the 90-93s are easily swapped w/o wiring modifications.

Heath

Does your Q have TCS or not and is the installed engine TCS?This would be the only reason you would have to change the harness and that involves just 2 wires under the plenum as well as swapping plenums.

where's the plenum on the Q45? what does TCS mean. I assume that my machanic knows what and where this is. if this was not switched would it make the sound I was hearing?

Here is a picture of a plenum – gets the air into the cylinders . I hope your Mechanic has a shop manual?TCS means traction control system.The first pic is a plenum with TCS.

This pic is a plenum without traction controll.If it is a TCS then check under the yellow-circled area in the previous post and insure that a Y shaped hose is solidly connected.

It sounds like you need to visit a Nissan or INFINITI dealer, preferably the latter and have the system checked with the Consult tester. Sometimes when major engine work is performed something gets put back wrong and the tester will tell you if something related to engine control is at fault.