Bill,

 

My take on what you are seeing is this:

When advancing the throttle slowly at the staging threshold of 15.5”, the controller stages. 

When it does this, the mixture goes lean.

When the mixture goes lean, the engine makes less power and the RPM decreases.

When the RPM decreases, the air volume required goes down and the manifold pressure rises even if the throttle setting hasn’t changed right then.

The increase in manifold pressure requires the controller to skip to the bins corresponding to the new manifold pressure.

 

As Ed suggests, looking at the oxygen sensor output (air-fuel mixture meter) will tell you if things are rich or lean at any given moment.  Looking at the fuel flow will be harder to interpret. 

 

Trying to adjust the staging conditions at a low manifold pressure makes it harder because the fuel flow change that occurs on staging is much more significant at low fuel flow rates than at high fuel flow rates.

 

Personally, I set the staging threshold as high as the primary injector flow rate will allow.  That minimizes the fuel flow change on staging.  At the density altitudes I have to work with, I seldom use the secondary injectors (stock 460 cc) and the engine makes more than enough power to fly safely.

 

Another thing that may be worth looking into is the RPM that the engine is running at when staging occurs.  For my controller, at least, looking at the mixture correction table address assignments page at the end of the manual, the addresses make a jump to a different part of the table at 3800 RPM.  If the system is staging at close to that RPM, then getting the system tuned may be even more difficult if the same part of the table isn’t being used every time staging occurs.

 

This makes sense to me… but I could be wrong.

 

Steve Boese

 

 

 

  

 

 

I have been working with staging for a couple of days and have my normal confusion. 

I have the Renesis engine but I have changed the red primary and blue secondary injectors to all yellow injectors.  This gives me roughly the same fuel flow capability when all four injectors are on, but a higher flow capability when only the primary are on as compared to the normal Renesis.

My staging point is set at 15 inches.  I know that is lower than Tracy recommends, but it reduces the cooling requirements while I mess with it.  I may change it later if I figure out what I am doing and get better (faster) at fixing the settings.

If I have the manifold pressure above the staging point and slowly lower it, it is a smooth transition and there is no indication that I can see or hear that the staging has changed.  BUT!

 

If I have the pressure below 15 and slowly raise it, it seems to me that the engine is trying to make a decision as I go above 15, until I get to about 15.5, then it suddenly makes a different sound and jumps to 16.0-16.5.  These bins are about 43 or 44 at 15 inches and it always jumps to 47 or 48.  The map table levels in this area are close to the same. 

I have not been able to determine if the change need is to lean or richen the mixture.  If you read the study Steve did, it would seem that it needs to richen??

I tried a suggestion I read of Tracy’s…I checked the fuel flow just below the stage point, 2.7 gal/hr.  then above the stage point.4.1 gal/hr.   This caused me to conclude that I needed to lean it, so I lowered it back down below the stage point to get started trying it and Whups! The fuel flow was still at 4+gal/hr!  I waited for it to lower but it didn’t???

 

I realize this sounds like I am rambling…..so what else is new!

 

Any insights would be welcome.

 

Bill B