Using Garmin G3x Lean Assist

[Max Clark]

I'm trying to figure out how to properly use Lean Assist with the G3x Touch. What exactly am I looking for to determine that I'm -50° LOP? The first cylinder, the last cylinder, the largest delta, the lowest delta?

https://support.garmin.com/en-US/?faq=WN2VewqSN41ZE3ZOaDiis6

My experience with the JPI EDM 730 was the engine monitor doing the work and automatically choosing the cylinder for you. Reading through their manual (https://www.jpinstruments.com/wp-content/uploads/2012/06/PG-EDM-730_830-Rev-A-02-JULY-2009.pdf) I understand that I was using the LAST cylinder to peak.

Page 22:

Upon reaching cruise configuration, use the LeanFind mode to identify the correct cylinder to reach peak EGT (for rich of peak this is the FIRST to peak, for lean of peak this is the LAST to peak). To change from one method to the other, just after activating LeanFind, hold STEP and LF and the other method will be momentarily shown: ROP or LOP. Release buttons after other method appears.

Page 27:

Lean Find-Finalizing the Lean Of Peak Mixture: The Scanner® Information Area displays the degrees below peak for the last (or richest) EGT to peak, giving you precise information necessary in setting the final mixture. Adjust the mixture to achieve the desired value below peak (using the digital EGT readout) or before engine roughness occurs. Caution: do not lean to the point where the engine runs rough. Note: the peak EGT value encountered during leaning can be recalled by holding the LF button. Tapping STEP exits the lean find mode and automatic scanning resumes.

Is this what I should be doing with the G3x?

[varlajo]

I lean to the point where the lowest delta meets my requirements, e.g. for 50 LOP lean to -58..-61..-50..-57 or some such. 

[Marc_B]

From my understanding, you don't routinely need to find the exact degree of LOP, but rather use fuel flow calculation applicable for your compression ratio to define %HP on the LOP side.  So I've always been a fan of the big mixture pull to the LOP side and just set the fuel flow once you've set your appropriate MP/RPM for cruise.

https://www.google.com/search?client=firefox-b-1-d&q=LOP+fuel+flow+calculation+site%3Amooneyspace.com

 

[varlajo]

2 minutes ago, Marc_B said:

So I've always been a fan of the big mixture pull to the LOP side and just set the fuel flow.

 

Totally agree, once you get to really know your engine. Took me a while to map fuel flow at various altitudes and to get used to some of my engine's quirks. 

[Max Clark]

1 hour ago, varlajo said:

I lean to the point where the lowest delta meets my requirements, e.g. for 50 LOP lean to -58..-61..-50..-57 or some such. 

If I’m following you’re using the last/richest cylinder to find LOP

[varlajo]

1 minute ago, Max Clark said:

If I’m following you’re using the last/richest cylinder to find LOP

Correct, the last cylinder to reach the desired LOP or ROP delta, which is not necessarily the last cylinder to peak. 

[Pinecone]

If you are leaning from ROP to LOP, you want to lean until the LAST cylinder peaks.  Then lean until that cylinder is the desired delta from peak.  When the last cylinder peaks, all the rest are already LOP.

What I do is a BMP (Big Mixture Pull) to a fuel flow that is well LOP.  Then I richen until the FIRST cylinder peaks, then lean that one to the desired delta.

If I wanted/needed to run ROP, I would lean from Rich until the FIRST cylinder peaks, then richen to the desired delta (at least 125 degrees ROP).

[midlifeflyer]

 

As everyone has said, leaning ROP is based on the leanest/first-to-peak cylinder.

Leaning LOP is based on the richest/last-to-peak cylinder.

With Lean Assist systems the system compares all the cylinders during the process and identifies the first/last to peak and In some you can tell it you are trying fo ROP or LOP and it will show you the appropriate values.

For most of us, once you know the value, you just go to it.

[Pinecone]

2 hours ago, midlifeflyer said:

For most of us, once you know the value, you just go to it.

This ^^^^

My cruise power setting is 29.5 inches, 2300 RPM, and 10.1 GPH.  I set that and am good to go.  I do sometimes use lean assist to tweak it, but it always comes out the same.

 

[Max Clark]

11 hours ago, Pinecone said:

If you are leaning from ROP to LOP, you want to lean until the LAST cylinder peaks.  Then lean until that cylinder is the desired delta from peak.  When the last cylinder peaks, all the rest are already LOP.

What I do is a BMP (Big Mixture Pull) to a fuel flow that is well LOP.  Then I richen until the FIRST cylinder peaks, then lean that one to the desired delta.

If I wanted/needed to run ROP, I would lean from Rich until the FIRST cylinder peaks, then richen to the desired delta (at least 125 degrees ROP).

Thanks - in Garmin land this is denoted with the hollow square box on the display.

 

[DC_Brasil]

I also do the Big Mixture Pull until I feel loss of power and enrich slightly so engine runs smoothly. 

This is what I got last flight.

Mooney M20J with IO-360-A3B6D. 

[midlifeflyer]

21 hours ago, DC_Brasil said:

I also do the Big Mixture Pull until I feel loss of power and enrich slightly so engine runs smoothly. 

This is what I got last flight.

Mooney M20J with IO-360-A3B6D. 

Yeah, the technique we were taught as student pilots often produces the same result. 

[bigmo]

I hate to admit I kind of do the same thing. If I follow my 930's advice precisely, I can control things a hair bit more...but the big pull, stumble, and touch of rich get's me a 98% solution.

@DC_Brasil I just wanted to point out that 141 ktas on 7.6gph is flipping amazing! I know Mooney owners can get zealous about economy, but I mean - come on - that's unreal.

 

 

[Slick Nick]

4 hours ago, bigmo said:

I hate to admit I kind of do the same thing. If I follow my 930's advice precisely, I can control things a hair bit more...but the big pull, stumble, and touch of rich get's me a 98% solution.

@DC_Brasil I just wanted to point out that 141 ktas on 7.6gph is flipping amazing! I know Mooney owners can get zealous about economy, but I mean - come on - that's unreal.

 

 

2300 RPM!

[varlajo]

On 2/12/2025 at 7:06 AM, DC_Brasil said:

This is what I got last flight.

How do you combine Main and Electrical in one tab in your G3X? Mine has separate tabs for Main, Electrical, and Fuel, which irritates me to no end.. 

Edited February 13 by varlajo

[Pinecone]

Don't know how to combine, but I have 2 tabs.  Fuel calc and everything else

[varlajo]

19 minutes ago, Pinecone said:

Don't know how to combine, but I have 2 tabs.  Fuel calc and everything else

Curiouser and curiouser.. 

[DC_Brasil]

6 hours ago, bigmo said:

I hate to 

@DC_Brasil I just wanted to point out that 141 ktas on 7.6gph is flipping amazing! I know Mooney owners can get zealous about economy, but I mean - come on - that's unreal.

 

 

On that day I was flying quite light. Only me (200lbs) a light backpack and the fuel.

I think it was the lowest FF I've seen so far. Usually my engine runs smooth around 8.2 gph.

[DC_Brasil]

2 hours ago, varlajo said:

How do you combine Main and Electrical in one tab in your G3X? Mine has separate tabs for Main, Electrical, and Fuel, which irritates me to no end.. 

I have no idea. It came that way from the shop.

[varlajo]

2 minutes ago, DC_Brasil said:

I have no idea. It came that way from the shop.

23 minutes ago, Pinecone said:

Don't know how to combine, but I have 2 tabs.  Fuel calc and everything else

What software version(s) are you guys running?

[Pinecone]

The latest.  At least as of last fall.  And it was working this way back in the summer when the project was delivered.

[PT20J]

Some of these displays do not appear to be configured properly per the STC. Engine gauge Display Option should normally be selected as Auto in configuration mode.