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-   -   Fuel pressure indications on Garmin G3X (https://vansairforce.net/community/showthread.php?t=195083)

Fltnut 05-06-2021 03:39 PM

Fuel pressure indications on Garmin G3X
 
I'm new to the forum and new to the RV12, so please bear with me.
The former owner had changed both fuel pumps for a "fluctuating pressure" problem. I don't call it fluctuating, it's more like crashing. It is very intermittent during cruise @ 7500 or 8500ft. Pressure goes to 0-2 then to 7.2, maybe 2 or 3 times, then back to normal. It may do that once or twice on an hour flight. It may not happen at all during the next 5 flights.
In my feeble mind it is an indication problem since there are no other indications of a problem. Has anyone else seen this type of problem on the G3X?

Ron

rcarsey 05-06-2021 09:27 PM

I don't have the legacy RV-12, so I can't address any specifics.. but there has been a few service bulletins regarding fuel pressure, which you may already be familiar with...

See SD-00017, SL-19-09-23 and N-18-07-12

If you're not sensing any change in performance/RPM..and since you say that the pumps have already been changed in an attempt to fix the problem.. then perhaps its just a sensor problem? According to the RV12 G3X electrical diagram, you have a Kavlico 101690-000 sensor.. which only measures up to 15psi...

Does the G3X need to know which sensor you have? I assume the Van's RV12 G3X default settings file will load that in automatically. (my rationale here is that the g3x needs to know that 0-12v maps to in terms of psi)

You can also try verifying that you have good electrical connections between the 3 wires at the fuel pressure sensor and the 3 pins at the GEA24 (apparently pins 1 2 and 4 of the largest D-sub connector).

You can also try just swapping out the sensor.

RFSchaller 05-06-2021 09:58 PM

I shouldn’t tempt fate by saying this, but my original VDO fuel pressure sensor has been rock solid for 9 years and 1100 hrs. On the other hand I had to replace the oil pressure sensor. Then about 100 hrs later it went squirrely. Of course I bought another only to find out it was the lead connection. Checking the electrical contacts is definitely a good place to start.

Fltnut 05-08-2021 03:08 PM

Thanks for your responses. I flew this morning and the pressure was all over the place after flying for about 30 mins.
I'm going to order a sending unit and go through the wires when I change it.

Rrhsch 05-09-2021 05:22 AM

Make sure the fuel line attached to the sensor is not touching the cooling hose to the radiator. This can cause the symptoms you are seeing.

cactusman 05-09-2021 09:02 AM

FUEL PRESSURE HOSE* FLUSH (* Left Side of Fuel Return Assembly)
1. Place rags beneath the Fuel Pressure Sender.
2. Loosen VA-216 Fuel Return Assembly hose coupling while supporting elbow with
second wrench.
3. Place container beneath hose and remove hose from fitting.
4. With end of hose inside container, flush hose by turning on fuel boost pump for
two seconds.
Installation
1. Reinstall hose to elbow.

RV12 MM Page 13-9

(Service Sked 18-5 says Fuel Pressure Flush should be done during Annual or 100 hrs)

My top ideas for you to check:

1. Purple gasket removal on Kavlico sensor
2. Electrical connections
3. Actual fuel pressure problems to include flush of hose above, gascolator screen, screen engine fuel pump for Rotax S/B replacement, engine driven pump drain line clog

Fltnut 05-11-2021 03:58 PM

Quote:

Originally Posted by Rrhsch (Post 1524217)
Make sure the fuel line attached to the sensor is not touching the cooling hose to the radiator. This can cause the symptoms you are seeing.

That's interesting because that's exactly where a zip ty is holding the line. That just got cut.

Fltnut 05-11-2021 04:09 PM

Quote:

Originally Posted by cactusman (Post 1524277)
FUEL PRESSURE HOSE* FLUSH (* Left Side of Fuel Return Assembly)
1. Place rags beneath the Fuel Pressure Sender.
2. Loosen VA-216 Fuel Return Assembly hose coupling while supporting elbow with
second wrench.
3. Place container beneath hose and remove hose from fitting.
4. With end of hose inside container, flush hose by turning on fuel boost pump for
two seconds.
Installation
1. Reinstall hose to elbow.

RV12 MM Page 13-9

(Service Sked 18-5 says Fuel Pressure Flush should be done during Annual or 100 hrs)

My top ideas for you to check:

1. Purple gasket removal on Kavlico sensor
2. Electrical connections
3. Actual fuel pressure problems to include flush of hose above, gascolator screen, screen engine fuel pump for Rotax S/B replacement, engine driven pump drain line clog

Thanks for the trouble shooting tips.
The previous owner said that he had done the "flush". I've already done sort of a flush. I just cracked the line and let the fuel pump run while I controlled the leak in an attempt to bleed any air out of that line.

Fltnut 05-22-2021 12:50 PM

Just an update. I separated the fuel pressure line from the cooling hose and for the last 3 hrs. of flying time the fuel pres. has been stable. I'll believe it's fixed after about 10 hrs.

Sclookout 08-25-2021 08:49 AM

Update
 
Any recent updates on low or erratic fuel pressure issues? I've tried a variety of suggestions from multiple threads, poured over hours of flight log data to identify a pattern, but no joy. I'm approaching 150 hours and still disturbingly random. No change in fuel flow or rpm just that pesky alarm?


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