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Cojaken
09-10-2021, 07:11 PM
I recently ordered and fitted a new replacement VDO fuel pressure sensor part # 41215, for my 3500EM non-S. I did this because the fuel pressure reading became erratic after about 270 hours.

The new fuel sensor reads way too high, over 10 psi running on the electric or mechanical pump.

I know the non-S systems don't allow you to pick the sensor type, but the calibration values are in the ENGINE.AFC file.

Here are the appropriate numbers from mine:

FUEL_PSI.NUM_CAL_PTS, 11
FUEL_PSI.DISPLAY_VALUE_1, 0
FUEL_PSI.AD_VALUE_1, 48
FUEL_PSI.DISPLAY_VALUE_2, 10
FUEL_PSI.AD_VALUE_2, 55
FUEL_PSI.DISPLAY_VALUE_3, 20
FUEL_PSI.AD_VALUE_3, 91
FUEL_PSI.DISPLAY_VALUE_4, 30
FUEL_PSI.AD_VALUE_4, 118
FUEL_PSI.DISPLAY_VALUE_5, 40
FUEL_PSI.AD_VALUE_5, 141
FUEL_PSI.DISPLAY_VALUE_6, 50
FUEL_PSI.AD_VALUE_6, 175
FUEL_PSI.DISPLAY_VALUE_7, 60
FUEL_PSI.AD_VALUE_7, 214
FUEL_PSI.DISPLAY_VALUE_8, 70
FUEL_PSI.AD_VALUE_8, 244
FUEL_PSI.DISPLAY_VALUE_9, 80
FUEL_PSI.AD_VALUE_9, 272
FUEL_PSI.DISPLAY_VALUE_10, 90
FUEL_PSI.AD_VALUE_10, 304
FUEL_PSI.DISPLAY_VALUE_11, 100
FUEL_PSI.AD_VALUE_11, 353

Do they look correct for the 41215 VDO sensor please and if so, do you think the new sensor could be bad?

I’ve checked the ground connection at the sensor and the back of the 3500EM and both are good.

My airplane is an RV- 9A with a carbureted O-320. The previous sensor read about 2.5 psi on the mechanical pump and about 5.5 psi when the electrical pump was running.

Colin

Shawn McGinnis
09-14-2021, 07:59 AM
The calibration is correct for a VDO 0-30 41,215.

If you disconnect the measurement wire and measure the voltage that the EFIS is providing what are you getting?

I've also seen people that have clogged reducer's causing issues.

Cojaken
09-15-2021, 09:56 AM
Thanks Shawn. I measured the voltage supplied and the resistance across the disconnected sensor at zero pressure.

The resistance is 9.5 ohms.

The voltage on pin 8 of the Engine Sensor connector on the back of the 3500EM is 4.157 V

The voltage at the sensor end of the brown wire is 4.15 V

All measurements with the engine not running.

Do any of these measurements explain the high pressure readings?

Shawn McGinnis
09-17-2021, 12:03 PM
Those numbers seem fine. Can you verify that 0-2bar stamped on the hex of the sensor?

Cojaken
09-17-2021, 01:31 PM
0-2 bar is stamped on the hex of the sensor

Shawn McGinnis
09-20-2021, 02:20 PM
Is the ground path shared or directly back to the EFIS?
Does the gauge read 0 psi before the engine is started or after cracking open the fuel system to release pressure?
How high does the pressure go if you just turn on the boost pump without the engine running?

Cojaken
09-21-2021, 08:28 AM
It is not easy to physically follow the ground wire, so to eliminate this as a potential problem, I ran a new temporary ground wire directly from the sensor to the 3500EM case. The behavior was the same.

The gauge reads 0 psi both before the engine is started and after cracking open the fuel system to release pressure.

The pressure goes to 9.4 psi with the boost pump on without the engine running. This is a little lower than before because I adjusted the shift, which is now 3.6.

Also, the 0.3 psi AD_VALUE read from the calibration screen is 25 and the 9.4 psi AD_VALUE is 207. That surprised me a little because it doesn't seem to correspond with the values in the ENGINE.AFC file. Maybe I am interpreting that incorrectly.

I sourced another sensor locally to try to eliminate the sensor as the problem and the behavior is the same, so I went back to the one I purchased from AFS.

Shawn McGinnis
09-21-2021, 02:35 PM
Seeing an adjust above 10% of the sensor range is normally a bad sign. If you drop the adjust back to 0 your previous 5.5 psi on electric boost lines up with AD_VAL 207 which is about 5.5 psi. The only odd one is the 0 psi being 25 AD_VAL.

568
FUEL_PSI.DISPLAY_VALUE_* happen to be tenths in the file.

Cojaken
09-21-2021, 05:35 PM
Thank you for the information Shawn.

I just made another observation. As you know when shutting off the master, the 3500EM switches to the internal backup battery for thirty seconds before shutting down.

I noticed that when this happens, the fuel pressure reading on the screen jumps from 0 psi to 2.4 psi and stays there until it shuts down.

Does that suggest anything?

Cojaken
09-30-2021, 12:46 PM
Shawn, thanks for our telephone discussion. As a result of our conversation, I got a Mityvac MV8510 Silverline Elite Hand Pump, adapters and a gauge and used them to check the calibration of the new VDO sensor.

These are the numbers I came up with and loaded on the 3500EM:
FUEL_PSI.DISPLAY_VALUE_1, 0
FUEL_PSI.AD_VALUE_1, 26
FUEL_PSI.DISPLAY_VALUE_2, 10
FUEL_PSI.AD_VALUE_2, 80
FUEL_PSI.DISPLAY_VALUE_3, 20
FUEL_PSI.AD_VALUE_3, 120
FUEL_PSI.DISPLAY_VALUE_4, 30
FUEL_PSI.AD_VALUE_4, 165
FUEL_PSI.DISPLAY_VALUE_5, 40
FUEL_PSI.AD_VALUE_5, 190
FUEL_PSI.DISPLAY_VALUE_6, 50
FUEL_PSI.AD_VALUE_6, 210
FUEL_PSI.DISPLAY_VALUE_7, 60
FUEL_PSI.AD_VALUE_7, 250
FUEL_PSI.DISPLAY_VALUE_8, 70
FUEL_PSI.AD_VALUE_8, 275
FUEL_PSI.DISPLAY_VALUE_9, 80
FUEL_PSI.AD_VALUE_9, 300
FUEL_PSI.DISPLAY_VALUE_10, 90
FUEL_PSI.AD_VALUE_10, 320
FUEL_PSI.DISPLAY_VALUE_11, 100
FUEL_PSI.AD_VALUE_11, 340

I now have confidence that my fuel pressure is reading correctly.

Thank you for your insight.

Shawn McGinnis
10-01-2021, 11:24 AM
Glad to hear you are fixed. Looks like a clean calibration.