Fuel Flow Fluctuation

[westcoastoz]

I have started to see some degree of fluctuation of the fuel flow on the Dynon EMS and suspect it may be an earthing problem so will pursue that first.

Is it just a case of checking that everything on the grounding pole is tight or should I remove all the terminals and perhaps treat the connectors with some kind of electro-lube?

Any tips based on past experience appreciated.

 

Dave

[Roger Lee]

Hi Dave,

 

There are about 5 grounding points to check before you blame it on the sender itself. There are 5 grounds to check out by the battery. There is the one up above the engine mount on the battery side that goes through the firewall into the instrument panel on the passenger side. These are all loose until a wrench is placed on them and proven otherwise. (Hand tight, but wrench loose) The one through the firewall needs to have a wrench on it from the engine side and then check the ones on the inside instrument panel side. If it is the bolt type that has all the ground wires on it, make sure you loosen the front nut most of the way out until you can get a wrench on the back nut against the firewall. If it is the flat long grounding block then tighten all the screws.

 

If this fails to fix the problem then pull the sender and squirt some carb cleaner with the little red tube on the nozzle in the small pin hole on the sender 4-5 times to clean it out of any old fuel.

 

If both these fail toss the sender and buy a new one. It is about $35-$40

[westcoastoz]

Hi Dave,

 

There are about 5 grounding points to check before you blame it on the sender itself. There are 5 grounds to check out by the battery. There is the one up above the engine mount on the battery side that goes through the firewall into the instrument panel on the passenger side. These are all loose until a wrench is placed on them and proven otherwise. (Hand tight, but wrench loose) The one through the firewall needs to have a wrench on it from the engine side and then check the ones on the inside instrument panel side. If it is the bolt type that has all the ground wires on it, make sure you loosen the front nut most of the way out until you can get a wrench on the back nut against the firewall. If it is the flat long grounding block then tighten all the screws.

 

If this fails to fix the problem then pull the sender and squirt some carb cleaner with the little red tube on the nozzle in the small pin hole on the sender 4-5 times to clean it out of any old fuel.

 

If both these fail toss the sender and buy a new one. It is about $35-$40

 

Thanks Roger,

Am going to the hangar today so will try tightening the earth (which is the bolt type) and see if there is any improvement.

 

I relocated the fuel pressure sender to the firewall quite some time ago and that is working fine however as your know, the fuel flow sensor is very difficult to access, so am hoping that is not the problem.

 

Dave

[Roger Lee]

Hi Dave,

 

You may have a .2-.4 normal fluctuation.

[Mike]

We have just had a 912 with fuel fluctuations on a digital gauge it turned out to be the valve unit in the mechanical pump had broken free from the casing didn't cause any running problems just fluctuations on the gage

 

 

 

So presumably the fuel was being sucked and blown on every pump stroke, so that the poor sensor impeller was sending mad pulses to the computer?

 

 

 

Mike

[westcoastoz]

We have just had a 912 with fuel fluctuations on a digital gauge it turned out to be the valve unit in the mechanical pump had broken free from the caseing didn't cause any running problems just fluctuations on the gage

 

 

Mike

 

Mike & Roger.....thanks for your input.

The fluctuations I am getting are up to 3L/hr (0.7 US gallons) so hopefully it is only an earthing problem. I expect the fluctuation in the case you mentioned would have been vastly more...?? I share a hangar with an RV7 which had a Dynon F.F. sensor go haywire (it was indicating in cruise anything from zero to 60 L.P.H.) so had to be replaced.

I cleaned and re-tightened all the earth points last week and intend flying today, so will see how it goes. I am dreading having to pull out the F.F. sensor as it is very inaccessible.

 

Dave

[Mike]

I have updated my post with some pics i know personally of 2 pumps doing this in the last couple of months one caused the engine to stop the other just caused fuel flow reading fluctuations both were on engines of around 1000 hours

 

Mike

 

 

Mike & Roger.....thanks for your input.

The fluctuations I am getting are up to 3L/hr (0.7 US gallons) so hopefully it is only an earthing problem. I expect the fluctuation in the case you mentioned would have been vastly more...?? I share a hangar with an RV7 which had a Dynon F.F. sensor go haywire (it was indicating in cruise anything from zero to 60 L.P.H.) so had to be replaced.

I cleaned and re-tightened all the earth points last week and intend flying today, so will see how it goes. I am dreading having to pull out the F.F. sensor as it is very inaccessible.

 

Dave

[Roger Lee]

Hi Mike,

 

Glad you found the problem as they certainly can be frustrating.

 

This is also why I have always recommend putting a separate in line mechanical test gauge on pressure issues to check to see if it is a real engine issue, a sender or a cockpit gauge. A mechanical gauge should have been able to detect this problem.