I'm posting this in an effort to save some of you MFI freaks from the same kind of expensive suffering I am now enduring. I just hurt my new 3.0 liter MFI motor through a very stupid mistake on my part. Here is a photo of the damage, just to kind of get started:
This is the aft side of the #1 cylinder, eroded away after the head gasket let go. The head is similarly damaged. It was actually blowing hot cumbustion gasses out forcefully enough to blow a hole through the adjoining chain box as well.
So, what caused this? In a word, "detonation". I believe the A/F ratio was going lean enough to cause severe enough detonation to seperate the head from the cylinder, on this, the least supported side of #1.
So how did it run so lean, after all of my work setting the A/F ratio with the LM1? Simple, in retrospect. I changed mufflers. Not just a little change, but a wholesale change, from an old Leisritz sport to a pair of M&K "track" mufflers. My old Leisritz was (unbeknownst to me) slowly giving up the ghost. A baffle or two finally let go a couple of days before an Alfa club track day I was to attend, and it was sounding like a Jake brake on a diesel truck under acceleration. So, wanting to run that track day, I put on the only mufflers on hand - the M&K's.
What I failed to do was to re-tune the MFI pump for the now much freer flowing exhaust. I had changed from a stock single out to a sport muffler years ago and did not have to re-tune, but this was a far more dramatic change in flow. A crapped out (probably enough to reduce its flow) old sport muffler to the very free flowing track mufflers. I should have known better. I should have hooked the LM1 back up and remeasured the A/F ratio. But, it was going to be "just for one day..." Expensive day...
Anyway, I've got the whole thing torn down and have inspected for "collateral damage" (pistons, cylinders, and heads, rod bearings, etc.). Everything else is just fine. I already have a replacement head and cylinder on the way. So, while I sit back and lick my wounds, I hope you guys can learn from my mistake.
MFI is a "dumb" system. Unlike CIS or Motronic, there is no mass airflow sensor, no feedback loop; nothing at all to "tell" the pump how much air is going in. That part is up to us, the tuners. Hell, even the lowly carburator is "smarter" than MFI; increasing air flow draws more fuel. Not so with MFI. And I knew that. I'm pretty upset with myself. Damn good thing I'm in good with my engine builder...