Lean mag check

[carusoam]

Thanks Paul!

I just learned something about my JPI and my mag timing from your post. 

Best regards,

-a-

[bradp]

Thank you professor Paul - I learned a lot by reading your posts.

 

[bradp]

Follow up question for koropates- how would a induction leak on cyl 3 look different on the monitoring data compared to a spark / ignition issue? 

[kortopates]

4 hours ago, bradp said:

Follow up question for koropates- how would a induction leak on cyl 3 look different on the monitoring data compared to a spark / ignition issue? 

An induction leak is an entirely different kind of anomaly - a mixture anomaly as opposed to an ignition anomaly. In a normally aspirated engine like your J, it will manifest itself when MAP is much lower than ambient atmospheric pressure, such as idle, and pretty much disappear when MAP equals ambient, such as WOT. One test for this is in our write up on Savvy Flight diagnostic using a 10" MAP reduction and comparing EGTs. But I really don't like this test. We use it because its the only test that works in carbureted engines but for fuel injected engines like your J I much prefer using gami sweeps. The gami sweep test is much more reliable, understandable by our clients and much more conclusive. The test is done by comparing baseline gami spreads done at WOT and low altitude compared to gami's done with no other changes except MAP is pulled back 10". RPM is used to reduce power to no more than 65% power to avoid higher than 65% power at low altitude. If there is an induction leak you will see that cylinder move to a much leaner ranking amongst its peers in very significant ways - such as from one of the richest to a lean outlier. If the cylinder is already one of the leanest in the WOT baseline, it may get so lean it flames out before the richest cyl peaks. Its generally very obvious. One of the big clues that gets us to suspect a leak is a higher than normal idle MAP, such as 15+" and an engine that won't idle smoothly at a slow idle. See the last page of this Savvy article on the principal behind the induction test but the article is using the basic test of 10" MAP drop in cruise that I dislike. https://www.savvyanalysis.com/articles/in-flight-diagnostics

Edited July 12, 2017 by kortopates

[carusoam]

I'm learning new things every time Paul posts something!

Best regards,

-a-

[wishboneash]

Thanks for posting all this info, Paul. A real treasure trove of useful information!