P0340 from hell

[LordFlash]

Sorry for a long post but I am in need of some help.

so I bought a non running 05 LGT sedan. Previous owner did head gaskets and mixed up the cam caps and the cams seized in the head. So I bought a set of ej204 heads from mag engines. As far as I could tell the heads were identical to the usdm heads with the exception of the combustion chamber being a bit smaller. 
so I rebuilt the engine.  Put the new heads on and it wouldn’t start and gave a p0340 camshaft code. New ( known hood used) cam sensor doesn’t change. So I discover the JDM heads had only 2 triggers on the cam reluctor instead of the USDM 3. So I change the camshafts. Starts right up and runs great. Problem solved? No.

As soon as the engine reaches operating temp or if you try to drive it engine stalls and code comes back. Change with another known good used cam sensor. No change. So I follow the FSM and go through all the diagnostic steps everything checks good. So I assume damn I have a bad ecu. So I took the engine out and put it in a different 05 legacy GT (same car just a wagon this time. Andddddd... Boom same problem. So I rebuilt another engine and put it in the sedan, ran great, no check engine light, sold it to my nephew who drove it until he hit a dear.
 

the code followed the engine So it must be something attached to the engine right? So I proceed to change the wiring harness, AVCS solenoids, AVCS sprockets, cam sensors. All have no effect. So I figure maybe is a ground issue. I install additional grounds nothing fixes the issue. At this point I figure “damn JDM heads are different some how”. So I rebuild a new long block put it in this second legacy and it runs great no code. So I now bought a third legacy GT, this one has a rod knock. So I rebuild the heads from that car, put the shortblock in that car and the exact same code and symptom up. I thought well it could be something on the same circuit pulling down voltage and or causing interference, so I replaced the throttle body and TGVs. The JDM heads I thought were the problem are now in my daily driver and have zero problems.
 

to summarize, this code has followed the engine into 3 different cars. the only parts that have yet to be changed (at least one or more times), are the shortblock, fuel injectors, wastegate solenoid, knock sensor.. 

im a decent professional mechanic, and I think I do well at diagnostics but I have no flipping idea where to go from here besides OHMing the injectors to see if they are causing some weird EMI through the power circuit.

[LordFlash]

One more tid bit. The car runs and drives beautifully if the driver cam sensor is unplugged. It’s been in a car I loaned to a friend for the last 18 months.

[rhino6303]

This is a big longshot (applies to different years), but you could check the clearance for the cam sensor. There is a TSB with the procedure and part numbers for spacers.

https://static.nhtsa.gov/odi/tsbs/2014/SB-10052498-5734.pdf

[LordFlash]

Yeah that thought crossed my mind a few months back. I don’t think that could be it because the problem has followed the shortblock. I’m basically resigned to putting a new shortblock in the car. I don’t understand how it’s the problem but ever car this block has been in has had the problem until I change the shortblock. I’ve heard of a Subaru with this problem before and it turned out that the cam had become magnetic. But I’ve changed the cam and heads. 

[rhino6303]

Did you change the wire harness from the ecu to the engine compartment? This is different from the engine harness.

[LordFlash]

The longblock has been in 3 separate cars. I did not swap the entire chassis harness or ECU when the engine was transferred from one vehicle to the next.

[rhino6303]

A couple of other thoughts to try. It might be electrical interference. Clear the code, pull the connector off the alternator and run the car to see if it comes on. A p0340 fault should come back pretty quickly.

A faulty starter with high resistance may also cause interference during cranking enough to throw the fault.