Fuel Flow indicating issue

[Mark89114]

I have a new to me Mooney Ovation with 310 STC and a Shadin fuel totalizer.  The transducer is mounted in a little box attached to firewall.

 

Engine starts and runs perfectly on first start of day with cold engine all indications on FF are normal. 

 

Hot starts is where I am having issues.  After shutting down for short period of time and attempting hot start, boost pump on high or low indicates NO FLOW.  I was at gas pumps, so I swore a bit and tried the different techniques for starting and did get engine started, ran like a top, but no initial fuel flow.  By the time I taxied over to hanger the fuel flow started working. 

 

I had this issue during initial annual/prebuy, MX looked at it, checked pressures, gascolator, etc. they said nothing wrong.  I flew it home and next hot start, same issue.  I had local MX look at it, they checked wires and canon plugs.  Didn't see anything.  

 

I can't image it is vapor lock as the transducer is mounted on firewall and far away from all of the "real" heat.  Someone else on MS mentioned fuel deposits and cleaning the thing as I guess it is simple.

 

Any thoughts?

 

[carusoam]

My understanding.....

The FF sensor is a spinning wheel with a magnetic pick up, I believe.

Having it stuck with deposits could keep it from spinning and registering.

I am not sure how well fuel flows around it when it is stuck, either.

It is probably easiest / most appropriate to have your mechanic remove and clean it, collect anything that falls out of it.

When it is working, what is the FF at take-off power?

I am only a PP, not a mechanic.

Best regards,

-a-

[Mark89114]

It is showing 26 gph on t/o. Again. It seems to work perfectly on cold start and after a couple of minutes after hot start does it come alive.

[carusoam]

Sounds like a vapor bubble is forming then getting stuck in the FF sensor...

Is your FF sensor wrapped in fire proof silicone insulation, like the more modern Mooneys?

Are you using the hot start procedure that circulates fuel back to the tank?

Some ideas from a PP, not a mechanic,

-a-

[shorrick mk2]

But *is* fuel recirculated back to the tank - the normal setup is a vapor return line, not a fuel return line?

[kortopates]

But *is* fuel recirculated back to the tank - the normal setup is a vapor return line, not a fuel return line?

 

Yes, on all the Continentals  when you pull the mixture back to ICO, and operate the boost pump the fuel divider prevents fuel from flowing forwards to the cylinders and the fuel pump circulates the excess fuel back through the fuel return line at the pump. The technique should be in your Ovation POH under hot start, my recollection it says you can use the high boost pump for short time like 15sec or the low boost pump for twice as long. See you POH or better yet, get a copy of Continentals Operators manual for your engine - that's were it came from. ​Earlier K's didn't get that wisdom added to the POH but its their in the Continental Operators manual and really helps.

Don't try that on a Lyc though as it will flood the engine.​

 

​

[Guest]

Continental continuous flow fuel injection and Bendix RSA systems are quite different. Continental fuel pumps have a vapour return system which returns approximately 50% of the consumption rate back to the fuel tank, Bendix does not.

Turning the fuel pump to "High" on a Continental system will kill the engine, while on a Bendix it only raises the fuel pressure with no operational change to the engine.

As stated above on a Continental system the airframe boost pump can be used to cool the engine fuel pump while the mixture is in ICO.

Clarence

[shorrick mk2]

On my Ovation when pulling the mixture back to ICO with boost pump the fuel divider certainly doesn't prevent fuel running to the engine as it will keep running...

[N177MC]

.

[Guest]

On my Ovation when pulling the mixture back to ICO with boost pump the fuel divider certainly doesn't prevent fuel running to the engine as it will keep running...

The airframe fuel boost pump when left on will cause a Continental engine to continue to run despite the mixture control being pulled to ICO.  This is completely normal.

Clarence