Scott,
Interesting about the observations on your LSE system.
Just to expand a little:
* I was getting considerably different readings between the two units.
* The suspect unit was at ~39degrees at 1,000 to 1,500 rpm (I couldn't take any more prop blast while holding the timing light), while the other unit remained near 25 degrees.
* Maximum advance should have been limited to 34 degrees as I had the low advance curve jumper installed (not the 39 shown on the suspect unit).
* Pulling the vacuum advance connection is supposed to remove any advance due to manifold pressure. Pulling the tube made no difference to the suspect unit (the other unit was already at minimum advance). However, I am not familiar with the exact dynamics between RPM, MP, and timing.
Finally, as more substantive evidence, I manually retarded the suspect unit by 15 degrees (ie, set the timing while at 15degrees ATDC, not TDC as is usual procedure. A test flight showed the temps back to normal. I have not yet received the manufacturer's findings.
Regards
Clark
On 12/7/06, Sky2high@aol.com <Sky2high@aol.com> wrote:
In a message dated 12/7/2006 1:06:47 P.M. Central Standard Time, bakercdb@gmail.com writes:
On the 2nd leg of a long cross country trip, I noticed that CHTs were running noticeably higher than usual on climb out. After leveling off at 6,500msl, CHTs were uniformly running approximately 40+ degrees higher than normal. Upon landing, the problem was eventually traced to one of my PMag ignitions that, was going to full advance at idle (39degrees). This was a failure mode of electronic ignitions that I hadn't considered before. Given the engine seemed to be running fine otherwise, I didn't try switching off one ignition in flight, which likely would have pinpointed the problem.
Clark,
Low MAP and low RPM are exactly the low power combination that encourages electronic ignitions to fully advance the timing. Indeed, the P-Mag may be broken (always delivering max advance), but a significant advance at idle is not a good failure indication. I regularly see 34-35 DBTDC at low RPM (idle or close to idle) and my base timing is 20 DBTDC because of a CR greater than
8.7 (equivalent to your 39 DBTDC unless your jumpers also are set for a base timing of 20 DBTDC).
Perhaps the P-Mag goes to a large advance because the MAP sensor is always indicating low pressure. What happens if you set the jumpers to use RPM only for the timing? You shouldn't get much advance for operation above 2500 RPM. I have to assume the RPM sensor is working for the P-Mag to operate at all.
PS: You may have experienced the kind of condition that led me to the conclusion that I must have a display of the in flight timing for any ignition that changes the timing.
Scott Krueger AKA Grayhawk
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