FlyingMonkey Posted August 16, 2014 Report Share Posted August 16, 2014 Hey all... I used to have low oil oil pressure readings. After having the oil pressure regulator changed to the new 2000hr TBO "mushroom" style, and the oil pressure sender relocated to the firewall with the Lockwood kit (with dual ground wires), my oil pressure has been great, a steady 45psi after the engine warms up. Lately my oil pressure has started to indicate lower, around 20-30psi when warm, even though it starts up at the normal 70psi or so. I checked all the grounds the sender wires, and they are all good. Then by accident I found the oil pressure came up about 5psi when I turned off the landing light (just an 11.5 Watt Soraa LED) on the ground. I then found that if I shut off my avionics master on the ground the oil pressure went up to almost 45psi -- normal for what I have been seeing. So clearly this is an electrical problem. Is it just a ground issue, or the sender wire being too small (it's tiny, probably 24ga), the gauge going bad, or something more serious like the alternator not able to keep up with the electrical load I'm putting on it? On the ground at idle I show 13.8V on the voltmeter. Here is what I have plugged in and usually run in flight: Dynon D100 Garmin SL40 Radio Garmin 496 Garmin 327 Transponder TruTrack Digiflight IIVS Autopilot & Servos Soraa 11.5W LED Landing Light Factory Beacon & Position Lights iPad 2.1A charger in the 12V accessory socket Factory analog tach and small gauges The only recent changes I have made are the autopilot installation (which I'm guessing is a bit of a power hog), and running the landing light all the time while flying. But surely other CTSW and CTLS have more stuff than this that they power like EMS, etc. I have a spare oil pressure gauge identical to the installed one I could put in to test, is that worth it or is the problem obvious to somebody reading this? I also might try flying with the autopilot turned off to see if that changes things. Now that I know it's electrical and not a "true" oil pressure problem It's not worrisome, but I would certainly like to have accurate oil pressure readings, and confidence my alternator is not weakening, especially since I'm planning to fly 1400nm to Page in October! Link to comment Share on other sites More sharing options...
Jim Posted August 16, 2014 Report Share Posted August 16, 2014 You need to post this on the Dynon forum. Sounds like either a ground loop or something's wrong with your D100. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted August 16, 2014 Author Report Share Posted August 16, 2014 You need to post this on the Dynon forum. Sounds like either a ground loop or something's wrong with your D100. Why blame the D100 right away for a problem with an analog oil pressure gauge not attached to the Dynon in any way except that they are both on the electrical system? Link to comment Share on other sites More sharing options...
chanik Posted August 16, 2014 Report Share Posted August 16, 2014 Because the Dynon ought to be able to compensate for voltage droop to the senders which are basically just variable resistors. They do not, I am well aware, but that is just poor design on their part. Link to comment Share on other sites More sharing options...
Jim Posted August 16, 2014 Report Share Posted August 16, 2014 What Chanik said... Link to comment Share on other sites More sharing options...
Tom Baker Posted August 16, 2014 Report Share Posted August 16, 2014 Guys, the Dynon D100 doesn't have oil pressure, it is all flight instruments. He has the small analog oil pressure gauge. Andy, check the grounds again. Check the capacitor. It sounds like a ground loop issue. Link to comment Share on other sites More sharing options...
chanik Posted August 17, 2014 Report Share Posted August 17, 2014 Ah, right, The D120 is the engine stuff. Analog gauges are almost all uncompensated. The variable resistor (sensor) throttles the current from a battery through the coil connected to a needle, called a d'arsonval movement. So lower resistance means more current but so does higher battery voltage. That's not a ground loop, just voltage rise on whatever ground rail the sender sits on (almost always connected as the sender to ground and the meter from positive rail to the sender). Run the landing light and measure with a DMM from the sender ground to battery -. I'd bet it floats up. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted August 17, 2014 Author Report Share Posted August 17, 2014 Ah, right, The D120 is the engine stuff. Analog gauges are almost all uncompensated. The variable resistor (sensor) throttles the current from a battery through the coil connected to a needle, called a d'arsonval movement. So lower resistance means more current but so does higher battery voltage. That's not a ground loop, just voltage rise on whatever ground rail the sender sits on (almost always connected as the sender to ground and the meter from positive rail to the sender). Run the landing light and measure with a DMM from the sender ground to battery -. I'd bet it floats up. Buried in that electrical engineering speak I don't really understand well, is there a corrective course of action? Link to comment Share on other sites More sharing options...
chanik Posted August 17, 2014 Report Share Posted August 17, 2014 Well, ultimately you need to fix the ground connection. You can tighten all your ground bolts like Roger recommends and use stabilent or caig labs electrical lubricants or, if you give up, run a separate ground wire directly to the battery from the negative side of the sensor. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted August 17, 2014 Author Report Share Posted August 17, 2014 One of the sensor grounds goes directly to the connection where the battery negative cable attaches. Is that sufficient, or does it have to go directly to the battery post? Link to comment Share on other sites More sharing options...
Anticept Posted August 17, 2014 Report Share Posted August 17, 2014 It shouldn't matter because it is such a small distance, but we've seen weirder. Just run it to the negative terminal to at least see if you should be worried about the sensor or something else. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted August 17, 2014 Author Report Share Posted August 17, 2014 I will recheck all the grounds and move the sensor ground to the terminal and report my findings. All my electrical stuff has been pretty good and stable, but oil pressure indications have been troublesome since day one of my ownership. Is that gauge particularly vulnerable to electrical conditions? None of my other gauges are having issues. Link to comment Share on other sites More sharing options...
Roger Lee Posted August 17, 2014 Report Share Posted August 17, 2014 You have a couple of options. First you could put a mechanical gauge on and just double check to make sure it is only a sensor issue and not real. Real oil pressure problems are fairly rare. You have an open port with a plug screw in it right in front of the oil pressure sender. It is 1/8" x 27 NPT threads. This does act like a poor ground. Since these are resistant type sensors a small change will affect the output reading. One easy quick dirty way to check it is to use a wire with alligator clips. Attach one right to the sender and then to the battery neg. Then start it and check for the drop. The next place to check is to do the same thing with the wire from a good ground right to the case of the D120. Did you put any thing on the oil pressure sending unit threads when it was installed? It can cause issues like this. Make sure all grounds are tight and if you don't have it yet install the extra ground I posted a while back in the maint. picture section. Dynon does recommend many times to add a separate ground wire to the case of the D120. Easy enough to see if this is an issue with a wire with alligator clips to a good ground. None of this should take very long and it's cheap and easy. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted August 17, 2014 Author Report Share Posted August 17, 2014 You have a couple of options. First you could put a mechanical gauge on and just double check to make sure it is only a sensor issue and not real. Real oil pressure problems are fairly rare. You have an open port with a plug screw in it right in front of the oil pressure sender. It is 1/8" x 27 NPT threads. This does act like a poor ground. Since these are resistant type sensors a small change will affect the output reading. One easy quick dirty way to check it is to use a wire with alligator clips. Attach one right to the sender and then to the battery neg. Then start it and check for the drop. The next place to check is to do the same thing with the wire from a good ground right to the case of the D120. Did you put any thing on the oil pressure sending unit threads when it was installed? It can cause issues like this. Make sure all grounds are tight and if you don't have it yet install the extra ground I posted a while back in the maint. picture section. Dynon does recommend many times to add a separate ground wire to the case of the D120. Easy enough to see if this is an issue with a wire with alligator clips to a good ground. None of this should take very long and it's cheap and easy. I didn't put anything on the threads. I really don't think it's a "real" oil problem, because this is very similar to what it was doing before I relocated the sender. I also can see the pressure rise when I turn things off, so I'm very confident it's electrical. I just don't understand how grounds can "go bad" over time. I have two ground wires on it now, I will move them around and see what happens. BTW Roger...what would you consider a minimum "non-worrisome" oil pressure in normal flight? Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted August 17, 2014 Report Share Posted August 17, 2014 ,,,. I just don't understand how grounds can "go bad" over time. I have two ground wires on it now, I will move them around and see what happens. Adding dedicated grounds complicates the system and introduces more points that might leak current to ground. Link to comment Share on other sites More sharing options...
mocfly Posted August 17, 2014 Report Share Posted August 17, 2014 Andy They away I fixed the ground problem on our oil temp was to run a separate wire from the oil temp body to the db9 connector on the back of the indicator. I fabricated a collar to affix to the probe, where the ground wire was affixed. This home run scheme was eventually done to all of our sensors. On another note once I got into the wiring of the gauges I was shocked by the scheme they used. Which did not follow the diagram. I am not sure how your system is wired when you have the Dynons. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted August 17, 2014 Author Report Share Posted August 17, 2014 I checked and tightened all the grounds, and pulled all the wires from the oil sender and cleaned all the ring terminals with a very fine grade Scotch-Brite pad. Then as chanik suggested, I took one on the two ground wires I had on the sender and moved it from one of the firewall grounds and attached it directly to to negative battery terminal. Weather kept me from flying long enough to be sure, but the signs are encouraging. The oil pressure stayed 45-50psi in all conditions, and with all electricals on, including the landing light and my iPad plugged into a 2.1A charger in the accessory socket. Voltmeter showed 14v+ at anything other than idle. At idle it dipped as low as 13.2v with everything on, but popped right to 14v with just a tiny throttle blip. I will fly it again ASAP and will report if the problem is solved. I realize the ground direct to the battery is a bit of a kludge, but once I verify the issue is solved I can find a more reliable ground point for the gauge. Link to comment Share on other sites More sharing options...
Roger Lee Posted August 17, 2014 Report Share Posted August 17, 2014 Do you have the additional ground wire I showed in a post? This has made a pretty good difference for many. Where did you have the ground wire hooked up to? http://ctflier.com/index.php?/topic/1459-resolution-to-common-ct-grounding-issues/ Link to comment Share on other sites More sharing options...
FlyingMonkey Posted August 17, 2014 Author Report Share Posted August 17, 2014 Do you have the additional ground wire I showed in a post? This has made a pretty good difference for many. Where did you have the ground wire hooked up to? http://ctflier.com/index.php?/topic/1459-resolution-to-common-ct-grounding-issues/ I don't have the wire you mentioned, it might be in my near future. The two grounds to the sender went to the voltage regulator ground point and the point on the firewall that the negative battery terminal attaches to. It now goes to the voltage regulator and directly to the battery negative terminal. I did find one of my other ground points snug but not really tight, and put a little more torque on it, though I don't think it was near loose enough to be an issue. Link to comment Share on other sites More sharing options...
Roger Lee Posted August 18, 2014 Report Share Posted August 18, 2014 All grounds are considered hand tight, but wrench loose. Put a wrench on all of them and make them TIGHT. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted August 18, 2014 Author Report Share Posted August 18, 2014 Sounds good Roger, thanks. You had told me this before and I had tightened them, all of them were still tight except the one I re-tightened. I'm going to fly again to make sure the problem is resolved by the direct-to-battery ground I have now. Assuming success, I will run your two #8 wire solution and then move the sender wire from the battery to the new ground attach point on the drip tray. That should ensure better grounding for everything and especially the pesky sender. Link to comment Share on other sites More sharing options...
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