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Final Approach
I've done the GAMI lean test twice now this week in my Cardinal, both times at 9000 MSL, OAT 0-3C, WOT 21", 2300 RPM, the only difference being that in between, my mechanic kindly swapped my front and back injectors. Both times I leaned from rich to lean, and found that the various cylinders peaked at the expected indicated fuel flows, with #3 and 4 peaking first and pretty much together, then #1 and #2, with #1 decidedly first on test 1, and pretty much together on test 2. The fuel flow spread between #3 and #2 is between 0.7 and 0.9 gph (#3 has a broad peak), which is about what GAMI says is to be expected on Lycoming engines with factory injectors. The rear cylinders (#3 and #4) run leaner than the front ones, also to be expected.
What was not expected: the first time, I stopped leaning after finding the #2 peak (~7.8 gph), because the engine was running quite rough. The second time the roughness was a little less, so I continued leaning in ~0.2 gph steps. The #2 EGT continued coming down smoothly. However, starting at 7.4 gph, the rear cylinder EGTs began rising again. The rise was most noticeable on #4 between 7.4 and 7.2 gph, when it jumped from ~1340 to about 1370. All CHTs continued to inch down (though they were already quite cool, #4 was about 240).
Any ideas on what this could be due to? My mechanic says he has no clue. Again, I do not know if it would have happened on the first test as I did not continue leaning after determining the #2 peak. Since I have my JPI set to read to the nearest degree, I notice a good deal of wandering and all of my EGT values are really +- 10 degrees, but the reversal of the downward EGT trend on #3 and #4 was greater than that (#1 also showed a slight rise from 7.4 to 7.2 gph as well, but I'd say it was not significant given the wandering).
Model info: 1976 Cardinal RG, IO360A1B6, 200 hp.
What was not expected: the first time, I stopped leaning after finding the #2 peak (~7.8 gph), because the engine was running quite rough. The second time the roughness was a little less, so I continued leaning in ~0.2 gph steps. The #2 EGT continued coming down smoothly. However, starting at 7.4 gph, the rear cylinder EGTs began rising again. The rise was most noticeable on #4 between 7.4 and 7.2 gph, when it jumped from ~1340 to about 1370. All CHTs continued to inch down (though they were already quite cool, #4 was about 240).
Any ideas on what this could be due to? My mechanic says he has no clue. Again, I do not know if it would have happened on the first test as I did not continue leaning after determining the #2 peak. Since I have my JPI set to read to the nearest degree, I notice a good deal of wandering and all of my EGT values are really +- 10 degrees, but the reversal of the downward EGT trend on #3 and #4 was greater than that (#1 also showed a slight rise from 7.4 to 7.2 gph as well, but I'd say it was not significant given the wandering).
Model info: 1976 Cardinal RG, IO360A1B6, 200 hp.
Lightly pressurizing the system is easy enough (you could do it yourself) followed by a soapy water spray at each joint will reveal any leaks. A LOP mag check (even slightly LOP) at high power will reveal any ignition system weaknesses. I would complete those tasks and if nothing is found, then it is time to call GAMI and get some new injectors.
