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Hi, I have a 1991 Nissan 300zx I purchased from a gentlemen who used it as a drift rig. I have engine swapped it as the one it came with had a thrown rod bearing. The new engine has 3-5k miles on it but had been sitting for 25-30 years. I drained all fluids and replaced all hoses and necessary wear items and it started right up and ran great after a little idle tuning. After a couple of days of driving it started misfiring and not idling correctly so I parked it and did a vacuum test and fuel pressure test which I have photos of, after some time I tried to get it home as the only issue came to be rough idle but no more misfire(just stopped misfiring)On the way I adjusted the IACV and the idle smoothed out and I had the car back running smoothly again. Did some exhaust mods(hollowed cats) and had some more great days with it (it would also shoot flames after 6k rpms and a quick shift) then one night I was cruising at 40mph in 4th gear going up a slight hill and heard a loud grinding sound sorta like the engine bound up. Rolled into a parking lot and towed it home. Since then it’s sat and I had accepted that it must’ve swallowed a valve or something requiring a engine removal again so I decided to try and sell. However just tonight I pulled the oil filter in search of any metal shavings proving my assumption and didn’t find any, I’m not sure if this means I’m in the clear but as of now I want to check 3 things. Timing, spark, and compression/valves. I understand how to check timing and spark and compression but I’m not sure what steps I can take to test the valves. I may already have an answer as well. In the pictures attached those tests were prior to IACV adjustment which could’ve been the source of a vacuum leak causing the fluctuations however the gauges were fluctuating when testing. Fluctuations were within 1-2 degrees so that could indicate a valve leak. I will retest the vacuum and finish other tests and update when I can. Thank you
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After letting it idle for a two-five minutes I pulled coil pack connectors one at a time and found that all of them changed the sound of the engine so I’m guessing I’m dealing with timing or valve train issues, fuel should still be good from my recent test. It was idling at 1500 rpms(prior to this issue I had it set at 750-1000 with accessories), I revved it up to 2000 and heard a clicking/valve grind sound from the driver side of the engine bay so I’m betting on timing. I will get a timing light and compression tester tomorrow. This car has been a rollercoaster and I just hope to get it in working order so I can store it for winter. (Winter is already here){shoutout to ALASKA for always being cold} update soon
 

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This is OP I lost access to my other account but turns out one of my exhaust valves on my driver side is either stuck, or not closing fully. Either way a new or reserviced head is needed. While attempting to warm up the engine for the compression test I did a quick paper test and put the fluctuating exhaust together with the tick at anything over 1,500rpms from the driver side of the engine as well as the cars proclivity to shoot flames when it was running and came to the conclusion that the heads gotta come off either way. Gonna end up selling it (moving state) sadly but this is definitely not the end of my Z career. ALWAYS MAKE SURE YOUR SWAP ENGINES ARE SOLID BEFORE PUTTING THEM IN. A lesson I learned the hard way.
 
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