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Chasing Cyl 1 Wiring Misfire; Looking for advice

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So i'm having one hell of a time with my newly build engine. After a drawn out fiasco with replacing long blocks after a botched diagnosis I discovered I had a badly hacked wiring harness causing misfires. Now with a new engine I replaced the harness with a used one I bought of ebay. Go figure the new one wasnt in great shape either, but still better than what I had.


Changing the harness fixed my issue initially but after a few days I got a P0021 code with a cyl 1 mis. After trouble shooting my self I checked my banjo filter (was already removed) and cleaned my cylinder bank A OCV with penetrating oil. This cleared up all the P0021 + accompanying codes and I went back to driving the car. Everything was functioning correctly and appeared to be normal on my AP (no knock, fuel trim normal, no roughness). After a couple days I got a P0340 code for a bad cam position sensor (bank A) and again a cyl 1 mis under building boost. I did a lot of research on this combination of codes and concluded my sensor was bad; I stopped driving the car and waited on the sensor to come in. This past Monday I replaced the bank A cam position sensor and it was a major PITA. After starting my car up after install the P0340 code was gone and the car was running perfectly, no issues. I let it idle for a bit to see what it would do and had no issues. As soon as I got in the car and reved it a bit (up to like 4k) I instantly got a rough idle and cyl 1 mis.


This was not the case before I installed the sensor, and would only get codes under hitting boost. The characteristics are identical to when my first harness was f***ed and after resetting the ecu it will idle fine with no roughness until I rev it or actually get out of the car and move the wiring harness around. FOR THIS REASON I believe it is the harness, I have also pulled the plug for cyl 1, checked the gap (0.032+/-) and installed a new stock plug with the correct gap. The plug which came out did not look bad but I replaced it out of principle; I have considered doing a compression test to make sure its nothing internal but have not yet. I also have cleaned all the connectors from the harness affecting cyl 1 (to OCV, Coilpack, Fuel Injector).


What im assuming is while I was in that region trying to install the sensor, I messed up the already shitty harness. I bought a new harness with a warranty and plan to install it as soon as I get the intake manifold gaskets in and a BPV hose which I will also be installing while im in there. Any other ideas on this issue i''d love to hear! To anybody (most people:lol:) more knowledgeable than me with tuning, could a data log help at all?




This is where I really would like advice, I've already removed the intake manifold to replace the first harness but it was with help from my mechanic at his shop which is about an hour away from me. I rather not tow my car all the way back to him to have him do the work and im very confident that swapping the wiring harness, by removing the intake manifold, is something im capable of lol. From what i've gathered + helped with its pretty straight forward. Unplug harness connections, remove battery and air intake to free up space, and removing any lines in the way of lifting up the intake manifold. From what i've learned on this topic from this site, Im planning on pulling the fuel pump fuse then starting the engine to relieve fuel pressure (in order to remove needed fuel lines) and my question to anyone who reads this is there anything else I should do/make sure of while doing this? Again I helped swap the first one so im not super worried but im just looking for any help other help on this issue.


At this point im fairly confident swapping on the new harness and getting a proper BPV (i have a 100% vent bov on right smh; Im putting on a 50/50 forge bpv) on it will solve my problem.. Planning on doing this whenever I have all the parts and time next week or weekend so any help would be appreciated in the meantime; Specifically im looking for what fuel/vac lines must be removed.

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