Increasing CHTs

[DanH]

With the CPI or EM-5 we can default the extreme ends of the MAP scale (shorted or open failures) to 0 MAP advance so you'd only have the base RPM setting of around 25 degrees total. (snip)

The EM-5 uses an external MAP sensor and will show an error code in the programmer and turn on the check engine light if there is a open or shorted sensor.(snip)

I'm not sure why any manufacturer would have 43 degrees programmed in on a Lycoming EI or why it would be designed in such a way to advance if the MAP signal is lost. Scary IMO.

I did some checking in reference to a open (or high resistance, low V) MAP signal with a Megajolt controller for an EDIS-based system. Like the above, a failsafe would require a user input to default the low manifold pressure (high manifold vacuum=low V) end of the ignition map to base timing. Easy to do; in the case of the Megajolt, just set some low figure (10", maybe 15" HG) as the lowest MP line, and enter base timing (20 or 25 degrees) for every RPM in that line. Now if the MAP sensor circuit craps out, you get base timing.

That's the open failure. Ross, check me; is there any practical reason to worry about a shorted failure? We're all setting the base timing with high manifold pressure, so a shorted sensor (5V signal) shouldn't make any difference.