NC Bill Posted October 13, 2014 Report Share Posted October 13, 2014 Immediately after annual (at that time 2 new carb float needles were installed and a crack in the exhaust was repaired) my fuel pressure sensor became erratic. It finally stabilized at 2.3psi for 20 minutes. Fuel flow and RPMs normal. Returned on my very next flight with same reading. Pulled the cowls and checked with calibrated gauge. Reading 1.8psi. Replaced the sensor - reading ZERO with both a/c and calibrated gauge. Replaced original sensor. Pulled the fuel line to the firewall and blew it clear - now 1 psi or less. Replaced fuel pump and finally got 3.3 psi after 2 engine starts. Flew 30 minutes home at between 1.5 and 2.3psi. Flew yesterday with same 1.5 to 2.3psi. All other gauges normal and engine runs fine. Thoughts or suggestions appreciated. Link to comment Share on other sites More sharing options...
Roger Lee Posted October 13, 2014 Report Share Posted October 13, 2014 Try putting a separate ground wire on the sender just to the battery negative for a test. I'm not quite sure about the post? You have a new sending unit and a new fuel pump? If these have both been changed then I would think poor wire connection. That said that doesn't rule out the very slim chance of another bad sender. Link to comment Share on other sites More sharing options...
Tad Olmsted Posted October 14, 2014 Report Share Posted October 14, 2014 Hello CT Flier!!! It has been a while. Roger, I ruled out a bad ground during troubleshooting. The fuel psi sender is a VDO and located on the firewall. I slaved in a calibrated mechanical gauge and determined the pump was bad. Everything was perfectly normal on the ground after the new pump install, but on takeoff it gets very low. I asked Bill to go straight and level WOT and he reports normal fuel psi. The Skyview is up to date and we still cannot pinpoint the problem. I am thinking of swapping out the VDO sensor for the 3 wire Dynon sender. I will have to run a 5VDC wire to the new sender, but PIN 18 is already in the Dynon EMS so it should be a painless mod. What do you think? Your opinion is greatly appreciated Sir. Bill, did I moss anything? Link to comment Share on other sites More sharing options...
Roger Lee Posted October 14, 2014 Report Share Posted October 14, 2014 It can be air in the system and it could still be a bad sender. If you put the mechanical gauge back inline and do a full power run-up does it stay reasonably stable? many will move a small amount from idle and first start to full cruise power. Link to comment Share on other sites More sharing options...
NC Bill Posted October 14, 2014 Author Report Share Posted October 14, 2014 Tad posted "I asked Bill to go straight and level WOT and he reports normal fuel psi." No. It reports 1.8psi or less. Link to comment Share on other sites More sharing options...
Tip Posted October 14, 2014 Report Share Posted October 14, 2014 Tad & Roger, Could it be a restricted pilot jet going to the fuel sender? Link to comment Share on other sites More sharing options...
Dan Kent Posted October 14, 2014 Report Share Posted October 14, 2014 Hello CT Flier!!! It has been a while. Roger, I ruled out a bad ground during troubleshooting. The fuel psi sender is a VDO and located on the firewall. I slaved in a calibrated mechanical gauge and determined the pump was bad. Everything was perfectly normal on the ground after the new pump install, but on takeoff it gets very low. I asked Bill to go straight and level WOT and he reports normal fuel psi. The Skyview is up to date and we still cannot pinpoint the problem. I am thinking of swapping out the VDO sensor for the 3 wire Dynon sender. I will have to run a 5VDC wire to the new sender, but PIN 18 is already in the Dynon EMS so it should be a painless mod. What do you think? Your opinion is greatly appreciated Sir. Bill, did I moss anything? Tad, Please don't take this the wrong way, as I'm hardly experienced enough to be giving advice to highly experienced LSA maintainers, but I guess I'm going to give some advice bases upon my experience, so take it for what it's worth. I have a low wing LSA, and had bad fuel pressure issues from when I took delivery of the plane (new) in Jan 2012. I was getting low reading many times, high readings occasionally, and I would say that during my flight training I most certainly hit the aux fuel pump more than the flap settings. Fortunately the engine never stumbled. About a year and a half ago, I switched to the Dynon fuel pressure gauge. I also got my 3rd fuel pump and since then I have had zero fuel pressure issues (of course I may not have had any issues previously, but was getting numerous bad readings). Just my $.02. Link to comment Share on other sites More sharing options...
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