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Fuel Sensor(s) question


2FlyAgain

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The fuel flow sensor on my aircraft started to get erratic.  The engine continued to run just fine.  I also have had issues with bad ground connections.  For the last two flights, it simply read 0.0 the entire flight.  This didn't seem to be a safety issue.  

 

Today as I was taxiing to the run up area, I got a high fuel pressure warning.  This has never happened before.  It was about 7.4 (7.5?) psi for a minute or two.  Then, it returned to normal.  I did a brief run-up to check the ignition circuits and it was still fine.  I taxied back to the hangar and shut down the engine.  I started the engine a couple of hours later.  The fuel pressure slowly climbed to 5.0 psi and after maybe 5-10 minutes settled at 4 psi.  

 

I have the new style fuel pump and read on another thread that it produces a higher pressure of up to 7.2 psi.  So, the momentary spike does not seem problematic from that perspective.  No, my engine monitoring settings have not been updated.

 

Is there likely to be any connection between my fuel flow sensor issue and the fuel pressure in general?  Is any thing else that I should check before flying again...?

 

Thanks in advance!

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Yes there could be.

First before any thing else tighten all 5 ground points. Everything in the engine compartment (4) and the 1 inside. Tighten them tight and they are considered hand tight, but wrench loose. In other words you have to put a wrench on each one especially the one that goes from the engine side firewall into the instrument panel side of the firewall.

 

If you have the new pump make sure you reset the max pressure and the yellow zone on the Dynon. max is 7.2 psi and I would set the yellow alert at 6.8. The normal pressure on this new pump can be any where from 3.5 to 6 psi with a majority around 5-5.5 psi.

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About electrical connections.

 

I have had a series of what I thought were continuity failures on several sensors on my CT. I blamed the connector, because I'd pinch the connector, clean it, apply conductivity goop and so forth and all would be better for a while.

 

Recently, I had occasion to change two female connectors. I noted that in both cases, the crimp of that connector to the wire was faulty. In fact, these looked like they were done by a flat jawed, common plier, not a crimper as we think of it. That may have been done when the firewall blanket was installed after production, I don't' know. After the connector was exchanged for a new one and joined with a proper crimp, I'd had no more trouble.

 

So, while you are checking for grounds, it might be worth your while to check the crimp. Most connectors use a plastic insulator that makes seeing the crimp difficult or at least not obvious. A gentle tug on the wire or some other test may give you confidence it is properly crimped or reveal it is not.

 

The bottom line is the ground circuit, like all circuits, involves the entire path, not just the ends.

 

My dad had a corn planter monitor that was intermittent and drove him crazy. After long frustration he finally went down every inch of the wire and found the electrical wire was butted together and covered with insulation which made it look good and it touched often, just not always. It must have happened during manufacturing. Splicing the wire fixed the problem.

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  • 6 months later...

Hello,

 

I have some tricky fuel pressure issues.

1. On take off the readings now can go down to red (2.2 psi) with audio alerts. Previously they stayed at about 4.9 psi +-2

2. They used to sit aroun 4.8-5 psi during cruise. Now varying between 3.1 and 4.8 psi. On start up they could go to above 5 psi, not anymore

3. I also notice that during taxi the fuel flow sometimes goes down to 0 liters per hour (very briefly) before going up when increasing power from idle. I did not notice this before

4. During cruise I noticed that depsite constant MAP I can see varying fuel flow displayed between say 15 and 21 liters (4 to 5.5 gallons) per hour when I expected it to stay reasonably constant on about 18 liters per hour (5 gallons) - as previously observed +- 0.3 g/h

5. Looking at SavvyAnalysis, previously during WOT take off the fuel flow was arount 8 gallons per hour, now I have recordings of max 6 (one flight) and max 7.6 (other flight) gallons per hour only (I believe recording intervals are 10 seconds, hence maybe it varyies as per cruise)

 

This first occured after a nice and normal 3.5 hour flight followed by parking at remote airfield overnight.

When tanks are full to top then both venting pipes on winglets can leak fuel when on ground - I assume normal

 

I have now changed the fuel pump

I have now changed the VDO fuel pressure sensor to a new one and it was worse (generally lower on start up and taxi down to yellow caution zone), hence changed it back to the orginal one for time being

Could install the solid state Kavlico one but still waiting for FD to give me Kavlico setting updates for Dynon, but no answer thus far

I'm not sure anymore it is the sensor alone given fuel flow observation and reading the grounding potential issue above

 

The engine seems to run fine.

 

The low warning pressure state usually appears on WOT when taking off and acceleration is full on just before or when rotating.

I'm not sure what else needs checking now.

 

Reading above ("First before any thing else tighten all 5 ground points. Everything in the engine compartment (4) and the 1 inside. Tighten them tight and they are considered hand tight, but wrench loose. In other words you have to put a wrench on each one especially the one that goes from the engine side firewall into the instrument panel side of the firewall.")

 

Where are the ground points I should check please? Can the Fuel Flow and Fuel Pressure readings be influenced by the same issue?

 

 

Thanks for your help, suggestions, or observations.

 

Matt

CTLS, 912 ULS Carbureted, Dynon Skyview

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