My friends and I recently completed an engine swap on a 2003 350z Enthusiast 6-speed. The motor was a JDM import and matches the trim of the current car. We did take off the harnesses and all the accessories (power steering, pump, alternator, starter, etc.) and used the old motor and chassis components, so those could be considered non-issues. We are leaning towards air, fuel, and spark, so I only mentioned the recent engine swap to consider electronics as well. Side note: friend is trying to keep it cheap since he is currently attending school without a job, hence the following.

1.) Explanation of problem/videos

-- When idling or being driven under 5500 RPM, the car is nearly perfect. A small, intermittent misfire sound can be heard when the hood is popped, but nothing major IMO. Under load, the car sounds like it is hitting the rev limiter at 5500-6000 RPM. This happens under load in any gear and does not change if slowly or suddenly accelerated to that point. See this video to hear the sound it makes when it accelerates to that point.

--In neutral, the car does rev higher and almost to redline, but is subject to a crackling/breaking up sound/kinda sounds like a burble tune. See this video for neutral rev to about 6500 or so.

2.) Known issues/attempted resolutions

-The following have NOT been changed: injectors and coil packs that came with the JDM motor were not changed and are currently being used. Fuel pump and wiring from chassis are the same.

-The car was sitting outside for about a 1.5 years with maybe 3-5 gallons in it. Friend added about maybe about 3 gallons of newer gas to this, so about a 50/50 mix of new and old gas.

-The only code the car throws is: P0300 "Random misfire or multiple cylinder misfires."

-The spark plugs were changed. This did not resolve the issue or code. The previous spark plugs were burnt up such that the gap in the electrode was a lot bigger. Cant remember how they looked in terms of fouling.

--My questions

-Has anyone else had this problem? I know, it seems obvious to just throw money at it to resolve it, but friend is pushing back and is trying to do it cheaply. I'd imagine the best things to do would to be adding more gas, testing the coil packs and injectors, and making sure there are no vacuum leaks, but is there a good order to this? Should we just hand it off to a shop to let them diagnose, might be better than having us try to test everything and throwing money at it?

 

Check the spark plug tubes for oil. If there's oil, replace the valve covers and change the coils. Check the harness very carefully to make sure you didn't pinch something during the engine swap.

 

I just posted about doing a JDM swap in a 2004. Where did you get the engine? I'm working on getting the engine out right now and haven't purchased the new one yet. I'm thinking about going with JDM Engine Zone. I'm also curious at any other 'heads up' notes you might have. Did you pull the engine out and leave the trans in? Or did you pull both out together? Good luck with the swap.

Thanks.

 

when we first got the replacement motor, SOME of the spark plug tubes, spark plugs, and the bottom of the coil packs were covered in oil. Unfortunately, i cannot remember which ones. That being said, we did replace the plugs and coils, so unless the valve cover gaskets are non-existant, I don’t think it would be an issue this early on when the new motor has less than an hour of run time.

 

hey, I’m unsure of where my friend got the motor from specifically, but it was a local engine importer place.

some heads up:
-keep the old US motor and all the accessories (pumps, starter, etc.)
-the accessories on the JDM motor don’t match up with the US harness, as in they have different connectors, so basically you’re gonna have to strip the motor to a long block then use the wiring harness and accessories from a US motor.
-the starter needs to be relocated to the passengers side. The JDM motor he got had the starter on the drivers side.
-otherwise, I think everything else was fine and was just used as is.
-there’s a really annoying connector that runs above the back of the transmission. We ended up cutting and splicing it after failing to undo it.
-tbh, the two worst things about the entire swap were: A. Exhaust and B. Actually getting the motor in.

-the exhaust bolts were so stuck on, literally a two day thing for us without melting them. I think we only got them off because we were using a 4 post lift and were able to stand underneath the car while doing so.
-we did leave the headers on while putting the engine back in the car, maybe you can do it without to get more room on the sides and to avoid hitting the steering shaft, but we chose to do it because we felt like we were gonna run out of space

-*****We chose to remove a power steering line that was in front of the transmission. Otherwise, you have to lift the motor over it and it becomes awful to do. Most people leave it in though.

- I would get one of those engine lift tilters to adjust the angle of the engine while putting it in.

-*********PLEASE PLEASE PLEASE make sure your flywheel is aligned before putting the motor in. It takes 2 seconds to do while putting the flywheel on the motor, but if you don’t, the car will not start or will run extremely rough. We had to pull the motor a second time when we realized our mistake