Propane and carb cleaner are good ways to check. Smoke test is probably the best way. I guess if it was me I would invest in tuning and datalogging. Getting a datalog gives you good info to at least point you in the right direction if not pinpoint the problem exactly.Hmmm... after reading that I think it might be worth pulling the lower intake to replace the gaskets.
I didn’t do a smoke test, but I did spray everywhere with carb cleaner, and when that didn’t produce any results I tried spraying propane. Also no results. I’m thinking I’ll try the lower intake gaskets since it’s cheap and I have no idea what else to try.
I got the lower intake off today, no real surprises there. The gaskets were definitely blown on the rear coolant passages. The intake port areas of the gaskets seemed to be fine, but hard to tell. It was the original 34 year old ford gaskets. If there had been a vacuum leak, would it be something easily visible? Also, the lower intake just lifted right off. Shouldn't the gaskets have been pulling it to the heads making it require at least some sort of force to remove it?
I'll reassemble tomorrow. The lower had about a half inch of sludge coating all of it, so I decided to soak it in purple power and then scrub it.