How did this all work out then, all back in and running?
Shooter
Not quite yet. I was going to wait until then to do one post summing everything up, but I may as well update you all. SC collected and delivered the engine back no problems, super fast service. I was a little bit disappointed that they tried to charge me an extra 90 quid for shipping though, but after a discussion we compromised and I paid the shipping for one way, and SC paid the other. Ended up being £475 altogether including the shipping and VAT (I always forget to ask about VAT), instead of £350. They also didn't fully run the engine in or do any power runs, due to keeping the time on the dyno down. They hadn't explicitly promised me they would do this, but I had sort of expected them to. Bit of a bummer but no big deal.
I have the engine back now. Turns out it was the throttle bodies completely out of sync. I never touched the actual mechanisms on them, as John had advised to leave them as they were from BMW. I did however unscrew them from their mounting rails so I could paint them individually. For those unfamiliar, they simply snap together with spring loaded clips, which can be further adjusted. John recons that even just removing them from the mounting rails upset the balance, which makes sense I guess. This had the effect of essentially blocking off air to 2 cylinders, and with the higher compression the engine just couldn't fire on the other 2. I kick myself for not being able to spot this myself...
From what John tells me, it fired up first time when they put it on the dyno, but it ran horribly. After that they couldn't get it to fire at all for a while, with the same symptoms I had described to them. This was when they started playing with the TBs, and after a few adjustments, in John's words, it ran 'like a Swiss watch'. They let it run for a good while, but said that due to how well dialed in the LT cams are from BMW, they don't need to be fully run it. I expect it was also to get it off the dyno quickly.
I got the engine back safe and sound on Friday, but it's been too cold for me to even think about working on the car, but with the warmer weather coming now, I hope to have it back in by the weekend, and running hopefully early next week. I'll hold full judgement until I hear the engine start for myself, but despite the hiccups, I'm still satisfied with how SC have handled the situation.
I'll keep you all posted on progress.
Edited by Chris1992, 15 February 2021 - 09:25 AM.
but admittedly not very thoroughly as I was so certain that the issue was something bigger like cam timing or ECU gremlins. I'm still remaining apprehensive until I've actually got the engine back in the car to see for myself if it really is fixed. 
