SOLVED - Bad pump, bad pressure sender, or something else?

[Thermos]

I've seen some small variations in fuel pressure since first flight, but on the way back from Oshkosh the variations became larger and more rapid. The engine ran flawlessly for the entire trip. Turning on the electric boost pump moved the average pressure up as you'd expect, but the fluctuations didn't go away. Here's a Savvy screen grab from the last flight before I left home for OSH -



and one from the next-to-last flight before I got home -



My RV-7 flies with a Superior IO-360 engine and G3X Touch avionics, including the original Kavlico pressure senders that came with the Garmin engine sensor kit in 2016. I'm on my way to the airport to double-check fuel line connections and bleed the fuel line to the sensor manifold. If the problem still exists after that, it's either the mechanical pump or the pressure sender.

I've been through some fuel pump failure threads here on VAF and this variation doesn't present like the failures I've read about - but I'm not an expert on mechanical fuel pumps. I'm leaning toward a sensor problem since I've read that the Kavlico sensor elements wear over time. Any thoughts from the experts on VAF?

Many thanks -

Dave

 

[rv8ch]

I'm leaning toward a sensor problem since I've read that the Kavlico sensor elements wear over time. Any thoughts from the experts on VAF?

I'm certainly not an expert, but I agree with you for two reasons: 1) the speed of change in your graphs seems to indicate a sensor or wiring issue; 2) you still had fluctuations with the electric fuel pump.

 

[Halleffect]

Other than trying another sender the best way to determine the real pressure is to attach a mechanical pressure gauge at the engine-mounted pump. The current senders from Garmin are a different design (GPT 75G).

 

[hgerhardt]

I recently had an issue with the Delphi/Packard connector on my Kavlico oil pressure sensor making intermittent contact. One day I got an indication on startup of 40 psi on my G3X. Checked the sensor by teeing a mechanical gauge and then both read correctly. Reconnected everything and had a good pressure indication again. A few weeks later, same thing. This time thinking it might be electrical, I gently moved the connector around and got some wild readings. Cleaned the contacts (even though they looked perfect), and it's been fine since.

If I have another issue, I'll replace the connector. The one I have is the pre-made jumper from Dynon. You can get the connector as a crimp-yourself version from Ballenger: https://www.bmotorsports.com/shop/product_info.php/products_id/2219

 

[lr172]

Looks like noise in the sender circuit. To me, it looks less likes a sender issue and more of a ground issue or some electromagnetic interference being introduced into the wire.

No need to bleed your sensor line, as that does nothing. Also not likely to be your pump having issues. It is not their nature to rapidly oscillate 1 - 2 psi. And even if they did, it is not a problem.

 

[Thermos]

Problem solved - based on everyone's feedback to this thread (thanks!) and some information found elsewhere on VAF, it seemed most likely that the Kavlico electromechanical sensor was developing a wear spot. So, I replaced it with a Garmin GPT 75G solid state sensor and the problem appears to be solved. The Garmin sensor isn't cheap but since it's solid state, I don't expect it will need to be changed for a long time.

Dave