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John - I took the TCM advanced engine training class last July. The instructor
gave a very plausible explanation about the rough idle problem, and what
they did to fix it. It seemed that the manifold pressure (MAP) sensors were seeing wide
fluctuations in pressure at idle. The problem was exacerbated by
lightweight props such as MT. They theorized that it was due to pressure
pulses traveling back and forth within the tuned induction system at
idle. The MAP sensor was getting inconsistent pressure readings from one
crank rotation to the next. Their first effort was to modify the ECU
software to sample the manifold pressure at a particular instant when
the pressure was relatively stable. They eventually settled on the simpler solution of drilling a small hole
in the throttle plate. This smoothed out the closed throttle airflow and
solved the rough idle problem. I am a firm believer in the benefits of the FADEC system. However, I am
just about at the end of my rope in trying to acquire one. I have been
emailing and calling Mattituck, Aerosance, and TCM about getting a kit
to upgrade my IO550-N7B. I can't even get anyone to return my calls, let
alone give me a delivery date! I have a few more feelers out, and after
that, I will reluctantly go back to mags and stock fuel injection. As a fallback, I plan to start looking at electronic ignitions such as
Lightspeed. However, improving the spark timing without doing anything
about the fuel injection is only half the battle. Does anyone know of
any other EFI systems out there?
Adam Molny
Legacy #151
Installing rudder cables, teflon power everywhere!
Subject: Re: [LML] TCM vs. Electrosystems Alternator
Date: Fri, 03 Dec 2004 11:19:02 -0500
From: "John Schroeder" <jschroeder@perigee.net>
The problem has been the software and more specifically the idle
speed/performance of the IO-550. It has something to do with the mass of
the prop, but that is not the only cause IMHO.
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