J_B wrote:
The "racket" reminds me of an enhanced spark knock in a gas engine under revs (in park, 1800-2500 RPM). It idles smooth at or near 750, which I believe is the norm...
You can remove the FCV entirely, or just the center disc from the shaft, it won't hurt anything to pull that. Unfortunately, you aren't going to like what I have to say now.
What you describe in the quote above, is JUST like what both of my engines sounded like before they were no more. Louder diesel rattling / clatter (especially at the RPMs you mention) is what the rod bearing failure presented itself as while engine #2 was also tapping away (sounded like a sticking valve and combustion going back into the intake) at idle. The tapping might not be present in yours right now at idle, but on engine #1 for me, it idled and even drove just fine during the test drive. Less than 10 miles later, it started clattering badly, the diesel sound got louder VERY quickly, and just as I was turning the key off... The #1 rod finished inverting (after beating the cylinder to shrapnel) and punched out the oil pan.
Noises are not fuel related on this engine. You have something VERY VERY badly wrong mechanically. To protect your block, I would quit while you are ahead and plan to pull the block and take it apart outside the engine bay.
This will be a world of suck for labor, sure... But the almost 90% certainty is that if you don't, you will be pulling the block anyway to replace it... Because it will then have a hole in it. The VM Specialist can sell you the internals to repair this one before it turns itself to scrap iron.