Not a typical LOP Ops Question

[schule]

During my nice long trip to Alaska I had time to experiment with LOP and have a question.

At 8500' the GAMI spread is right at 1 GPH, however at 12500' the GAMI spread is right at .7 GPH.  #2 is the richest and #3 is the leanest in every test.  

This only allows me to go to around 10-15 degrees LOP before the #2 EGT starts to rise and the engine gets rough.

Is it normal for the GAMI spread to decrease with altitude?

 

-Mark

[Cruiser]

there may be some difference due to power levels. You should probably do a GAMI check at both low and high altitude at the SAME POWER SETTING. IF the spread is different there may be an intake air leak to one of the cylinders.

[Parker_Woodruff]

What make/model engine do you have?

[KSMooniac]

Quote: schule

#2 is the richest and #3 is the leanest in every test.  

This only allows me to go to around 10-15 degrees LOP before the #2 EGT starts to rise and the engine gets rough.

 

[schule]

Scott what you are saying makes sense.  The #2 always is the first to peak and #3 is always the last to peak.  So with #2 established as the leanest and #3 as the richest; #2 starts to run rough around 50 degrees LOP on that cylinder with #3 at 10-15 degrees best case.  The #1 & #4 get about 30-40 degrees LOP prior to #2 running rough.

I have a NA IO-360 A3B6.  I am trying to take any ideas on previous lessons learned before going to the mechanic with a blank check.  Are leaks in the induction difficult to find?  Could it be the magnetos or spark plugs?

I like the idea and options created by saving around 2 GPH LOP vs safely ROP, but I do not want to kill the engine if it is not properly set up.

[Shadrach]

Your posts contradict each other regarding which cyl are peaking 1st and last. 

[KSMooniac]

I would definitely check for induction leaks first.  You can do this by lightly pressurizing the induction system by using a filtered shop vac blowing through the ram air inlet (if you have this) and tape-off the air filter box.  You might need to get creative with some cardboard and duct tape to make an adapter for the vac hose to fit.  Make a bottle of soapy water solution with dish soap, and liberally spray all of the joints at the cylinders and the sump.  You should see action plainly enough, and perhaps even hear a whistle if the vac is placed far enough away.  An air compressor could be used as well at a low setting.

You could clean all of the injectors as well with Hoppe's #9 (gun cleaner) and make sure they're not clogged, but this is less-likely than an induction leak unless you've done tank work recently or otherwise have deteriorating sealant or other crap in your fuel system.  Be careful about contaminating them with shop rag lint after they are clean.  A magnifying glass, lots of light, and compressed air are useful too.

Next you could clean & gap all the spark plugs AND check their resistance levels between the center electrode and the input side where the spring from the lead contacts it.  They should be nominally around 1000 ohms, and be replaced if they are 5000 ohms.

Finally, check the ignition leads for obvious defects.  If you mags haven't had a 500 hour service on schedule, then maybe you should get that done as well.

Good luck!  It is worth the effort.

 

[John Pleisse]

My favorite:

metallurgy  (m?'tæl?d??, US  'm?t ? ?l??d??) http://www.mooneyspace.com/help/luna/IPA_pron_key.html' target="_blank">
— n
	the scientific study of the extraction, refining, alloying, and fabrication of metals and of their structure and properties
metal'lurgic
— adj
metal'lurgical
— adj
metal'lurgically
— adv
metallurgist
— n

[BigTex]

You might want to think about having your injectors tuned to tighten up your GAMI spread.  If you're a member of EAA you might want to watch a nice webinar that Mike Busch with Savvy Aviation did on leaning basics.  Here's the link:  http://www.eaavideo.org/video.aspx?v=994986557001

 

[rahill]

Quote: schule

Scott what you are saying makes sense.  The #2 always is the first to peak and #3 is always the last to peak.  So with #2 established as the leanest and #3 as the richest; #2 starts to run rough around 50 degrees LOP on that cylinder with #3 at 10-15 degrees best case.  The #1 & #4 get about 30-40 degrees LOP prior to #2 running rough.

I have a NA IO-360 A3B6.  I am trying to take any ideas on previous lessons learned before going to the mechanic with a blank check.  Are leaks in the induction difficult to find?  Could it be the magnetos or spark plugs?

I like the idea and options created by saving around 2 GPH LOP vs safely ROP, but I do not want to kill the engine if it is not properly set up.

[schule]

All,

Thanks for the ideas.  I will start checking the spark plugs and go from there.  Thanks for the clarification that FIRST to PEAK = LEANEST (#2) and LAST to PEAK = RICHEST (#3).

After months of waiting it is nice to finally have my bird home where the real learning can begin.

-Mark

[Lionudakis]

I'd start with checking for induction leaks, something you can do yourself, as KSmooniac stated how.

Dealing with spark plugs, I bought a spark plug tester last year, it shows a lot, regardless of impedances, or condition, actually seeing the spark with airpressure applied shows how the pug is operating. I now routinely clean, gap and test, as part of my regular maintenance and have found several that were sparking different than the rest or not sparking where they were supposed to be, especially important running LOP