Weird Misfire

[bobyknish]

So, a little bit of backstory:

1991 300zx, pistons crushed valves in April 2016 due to a ramey Z idler stud breaking. I bought a rebuilt engine off craigslist, and swapped it.

When I bought the new engine, it came with mismatched phase 1 injectors. I figured I'd just replace them all with my broken engine's injectors, since they were all new.

BUT,
Just recently I was looking at the heads and block for identification, in an effort to fix a misfire/running rich/vacuum leak, when I noticed that the heads on the new engine were 10Y heads, or 93-96 NA heads.

Here's where I am now:
I have phase 1 injectors (1991 fuel rail) installed on the lower intake manifold (phase unknown) with Phase 2 heads.

The car's symptoms are:
-Vacuum leak from around plenum area, but exact location is unknown
-The car runs slightly rich, as the rear bumper is getting coated in blackness
-there is a slight misfire that can happen on either bank of cylinders at any random time (true dual exhaust)
-hunting idle

Injectors and coil packs all ohm out correctly, spark plugs are correct with no obvious wear, fuel rail insulators are fine, plenum gasket has been replaced 3 times trying to solve this issue.

Only CEL code is 35 (egr delete)

Any ideas?

[Hijacker]

Have you checked timing? Also, have you done any other work such as new cams, ECU reflash, etc?

[bobyknish]

Timing is perfect at 15 degree (done with spark plug wire), and to my knowledge the engine is otherwise stock, except for minor bore, since it had brand new pistons when I bought it

[Challenger266]

I suggest replacing the plug wires, cap, rotorn and crank angle sensor. The random misfire could be a result of worn ignition parts or the CAS ( crank sensor) throwing funky readings. If that doesnt do it, mas air flow, then O2 sensor. Either running rich from the misfires or its getting incorrect data from maf or o2 sensor.

[DCaff300ZX]

I suggest replacing the plug wires, cap, rotorn and crank angle sensor. The random misfire could be a result of worn ignition parts or the CAS ( crank sensor) throwing funky readings. If that doesnt do it, mas air flow, then O2 sensor. Either running rich from the misfires or its getting incorrect data from maf or o2 sensor.

The VG30DE and DETT do not use a cap and rotor, they use coil packs on each spark plug.
However, the basic ideas you suggest are correct in checking the CAS connector and coil pack connectors for continuity.
Also a huge suspect and that fits your issues is the Idle Air Control Valve, IACV. The connectors get brittle and/or corrode, the hoses also, and the unit itself is also notorious for failure but sometimes can be coaxed back into life.
The Power Transistor Unit (PTU) harness connectors and also the Coolant Temp Sensor (CTS) connectors also can cause issues due to corrosion.
Time to have some Z fun!

[bobyknish]

So today I was examining my old lower intake plenum when I noticed that it did have a casting ID number.
So my current running engine has 10Y heads and a 30P lower intake manifold.

I have a strong suspicion that the vacuum leak is coming from where the manifold mates with the heads.

Any idea on where to go from here? All my engine management stuff is phase 1, only the heads are phase 2