A while back we talked about how our tach and digital message center hour meters don't even come close to matching. This is wierd since both are driven by the same computer (MMDC). In my case, the tach shows 250 and the Message Center says like 120. This impacts service intervals, GPH calcs and even resale value.
We speculated that maybe the tach increments when the key is turned to the ACCY position (ie. floating with radio on).
During my January annual service and a few hours of wakeboarding, I recorded both indications before and after, and they both incremented the same number of hours, and they only incremented when the engine was turning. This is as we'd expect and hope. Normal operation.
Which leaves the question, when/how did the two numbers diverge 130 hours? Also, which one's correct? My GUESS is that the tach hour meter may be calculated INSIDE the tach, ie. if the engine's turning (needle's non-zero) the meter counts. This would mean that at sometime around the 130-hour mark, my MMDC was replaced or reprogrammed and the digital version of the hour meter was flushed. Just a guess.
This question does seem important to me, because I don't want a single point failure to wipe my hour record. If both indicators are driven directly from the MMDC, then an MMDC will kill the record. I've thought many times it would be wise to install an old-school hour meter on the engine (hotwire it to run until the current hour is reached then install and forget). Although that would probably still be wise to do, I'd feel a lot better if the tach is in fact recording its own figure independent of the MMDC (sort of independent; maybe indirectly would be a better word).
Does that make sense, or has the coffeeee beeeecome a communication barrier?
