Did a big project and put a motor from a rusty 2003 into a clean 2004. Motor ran fine until I started the car back up for the first time. Have thrown camshaft sensors, MAF, knock sensor, injectors, plugs, throttle body, and now I’ve recently tried pinpointing it as the time chain. With that still not working I’ve realized I’m out of ideas. The car will start and run for about 5-10 minutes and slowly choke itself out. I cannot rev it past 2500 rpm’s. And I have to slam my foot to the floor to get the needle to move at all really. There’s a small amount of blueish smoke coming from the back and it smells very rich. The only code I can get anymore is a p0300. I was just wondering if anyone has ever had something like this happen. The engine also has good compression and I used a smoke detector to find vacuum leaks, to no avail. I know it’s a long read but any suggestions could really help right now. Thanks in advance everyone, sorry if I’m light on info didn’t wanna write a novel in one post.

 

When it's running during that initial startup before it chokes does it sound like it's running normally?

P0300 is random misfire, you didn't mention anything about spark plugs and coil packs. Are they the ones from the donor engine, old engine?

Typically when I swap a motor I keep ALL the sensors from the original motor if I knew it wasn't throwing any error codes on the old setup. By adding a bunch of other newer sensor to the mix it makes it INCREDIBLY difficult to pinpoint issues since it could be almost literally anything.

If it doesn't run normally on the initial start I would suspect the flywheel/flexplate didn't get clocked to the correct position on the crankshaft (it only installs one way, it will literally bolt up in any configuration but you MUST align the dowel on the crankshaft to the detent on the flywheel/flexplate or the crank sensor reads wrong).

Or you have bad cam/crank sensors, if they're not genuine Nissan or Hitachi (the OEM manufacturer) sensors then replace them, swap the original ones back in.

Since it smells like it's running rich I would suspect the flywheel/flexplate didn't get clocked properly. Was it removed from the engine?