so i installed a jdm headers n y-pipe on my 1997 nissan maxima which had vq30 wit 169k on it n after i pickd it up my check engine light came on n started flashin n scanned it n it came wit cylinder 5 misfire i checkd it n found out that the moron who put it on forgot to plug in my coil pack i did plugd it back in n changed the whole plugs 3 days later my engine blew on me on the highway which im stil to find out why. i jus dropped a new vq30 engine from a 1995 max n i started it up n it came up wit cylinder one misfire n my check engine keeps flashin when im drivin down the road same thin it was doin on the old engine, im doin the plugs n swappin out the coil pack n check the injectors, does anyone have any idea as to wat wud do that cuz i really dont wanna lose another engine

Ok, if your MIL is flashing and cyl 1 is misfiring I'm assuming you have these faults P0300 and P0301. Swap cyl 1 ignition coil with another cylinder. If the misfire follows the coil then the coil is to blame. If the misfire does not follow swap the spark plug, if the misfire does not follow the spark plug check the power/ ground to cyl 1 coil and compare it to a cylinder thats not misfirng if you find no problems there check cyl 1 with a compression gauge and compare it to another cylinder thats not misfiring and compare it to the repair manual spec. If you find no problems there, Let your engine cool down, remove your spark plugs, rotate the engine so that cyl 1 is at TDC. remove you radiator cap. Measure your coolant temp either with a thermometer or with a voltmeter back probed on the coolant temp sensor. Attatch a cooling system pressure tester. Apply 1 bar (14.7psi) of pressure and let the car sit for a long time. I ususally let the car sit overnight. Check to see if you have a drop in pressure if you do check the coolant temp again, if the temp is much lower than you may not have a leak since pressure will change with temperature but get a wire coat hanger and bend it in the shape of a hook, stick it in cylinder 1 spark plug hole since thats the cylinder thats misfiring. Check for coolant residue. If any coolant is found Remove the head, check the crankcase and head surface for warpage, if any is found have the affected parts machined, and replace your head gasket