FlyingMonkey Posted December 7, 2015 Report Share Posted December 7, 2015 Hey all... Since I got my CTSW, I have battled oil pressure indication issues. My oil pressure is fine at startup, then degrades over the course of operation. Once warmed up, my oil pressure indicates 20-30psi, sometimes as low as 15psi. I know it's an indication issue, because if I switch off the avionics master the pressure immediately jumps 10-15psi. I have: * Checked and tightened all grounds, and even added a ground wire from the sender direct to the negative battery terminal * Replaced the oil sender (twice). * Relocated the sender to the firewall using the Lockwood kit. * Replaced the oil pressure gauge (I had a spare factory gauge). I really thought replacing the gauge did it; oil pressure was rock stready at 45-50psi at all times once I changed it out. That lasted for about a year. Coming back from Page I noticed it indicating 30-40psi, and the last couple of flights it has been even worse, 15-25psi. Again, switching off electrical devices brought the pressure back up. I'm kind of at a loss for what is going on here. I know it's not reading correctly, but not having accurate oil pressure indications is not a really safe way to fly. Any ideas? Link to comment Share on other sites More sharing options...
Roger Lee Posted December 7, 2015 Report Share Posted December 7, 2015 I hate to say this, but try another sender. Link to comment Share on other sites More sharing options...
FredG Posted December 7, 2015 Report Share Posted December 7, 2015 Andy, do you have a way of monitoring charging system voltage when you turn off the avionics master? (It can't think of a way that turning off the avionics master would affect indicated pressure if it weren't affecting voltage.) Also, do I remember correctly that you have an analog oil pressure gauge? Link to comment Share on other sites More sharing options...
cdarza Posted December 7, 2015 Report Share Posted December 7, 2015 Well, the timing of your post is just perfect for me.... I too once again had a flight last Saturday with the analog gauges (not just the oil pressure) bouncing all over the place. (Sorry i am not able to offer a solution- haha) I too wish this recurring problem could be solved. I hope the day does not come that i do have a issue with the oil pressure and simply blame a bad grounding or bad gauge and ignore a potentially big problem. In my case, i believe it was a bad ground? As i wiggled the ignition switch(key) the CHT and oil tempwould move erratically. Oil Pressure would hit red line - then down to 70.....50..... 30 back up to red line.....etc etc. https://youtu.be/2UTY-zz-E10 Link to comment Share on other sites More sharing options...
FlyingMonkey Posted December 7, 2015 Author Report Share Posted December 7, 2015 That's right Fred, analog engine gauges. The problem is I don't have all of the indications that the D-120 & Skyview users have. I only have oil pressure, volts, oil temp, and CHT. Certainly all you need to run a Rotax engine, but it makes it harder to troubleshoot. The analog voltage gauge will still indicate with the avionics master off, you have to turn off the bus master to kill it. IIRC I usually see about 13.8-14.0v with everything turned off, and about 13.0-13.2v in flight with everything running. Those numbers have been consistent as long as I have owned the airplane. cdarza, my gauge is not "bouncing" between values, or jittery at all. It's buttery smooth, and the pressure number will just slowly leak down lower over time. It did scare me one time by going from ~30psi to about 10psi in a few seconds, but as soon as I landed (I was in the pattern) and switched off the avionics it climbed back up to about 40psi. Roger, the senders are pretty inexpensive and I can pop another one in, especially now that it's on the firewall and easy to get to. But just as a thought experiment, if that didn't cure the problem, where would you look next? I guess it could just be that the sender is failing and needs higher voltage than normal to read correctly. If that is not it, it's going to be something electrical and probably a little harder to find. Curt, where are you?!? Link to comment Share on other sites More sharing options...
Rich Posted December 7, 2015 Report Share Posted December 7, 2015 Andy, Possibly battery or battery connection? Link to comment Share on other sites More sharing options...
FlyingMonkey Posted December 7, 2015 Author Report Share Posted December 7, 2015 Andy, Possibly battery or battery connection? I don't think so. The battery cranks the engine right up, my volts show good on the gauge (about 12.6-13.0v on the battery only with engine off), and no other electrical devices are showing any problem. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted December 7, 2015 Author Report Share Posted December 7, 2015 I just ordered a new sender. I think the part number Lockwood uses for the firewall mounted sender is different from the normally engine mounted one I have, so maybe that will make a difference. If not, it never hurts to have a spare sender on hand. Link to comment Share on other sites More sharing options...
procharger Posted December 7, 2015 Report Share Posted December 7, 2015 Sender from Jegs is $41.00 is VDO 360-004 someone correct me if I am wrong?? I just got one for my HKS 700 E engine Link to comment Share on other sites More sharing options...
procharger Posted December 7, 2015 Report Share Posted December 7, 2015 912/914 Oil Pressure Gauge and Sending Units 7 KUL 94 Page 2 of 2 2. VDO VDO oil pressure sender part no. V360 003 (5 bar) is to be matched to VDO oil pressure gauge V350 040 (0 - 80 PSI). VDO oil pressure sender part no. V360 004 (10 bar) is to be matched to VDO oil pressure gauge V350 041 (0 - 150 PSI). The quickest way to identify whether or not your engine has the correct pressure gauge and corresponding sending unit is to visually verify the 0 - 5 bar or 0 - 10 bar stamped on the sending unit hex nut (see Figure 1) and assure such is matched to its corresponding 0 - 80 PSI or 0 - 150 Link to comment Share on other sites More sharing options...
FlyingMonkey Posted December 7, 2015 Author Report Share Posted December 7, 2015 Here is the one I ordered, that Lockwood said is correct: http://www.lockwood.aero/p-2214-oil-pressure-sender-for-relocation-kit-2-prong-1-for-ground.aspx It's a VDO GAV360-430. VDO's website lists that unit as 0-150psi. Link to comment Share on other sites More sharing options...
procharger Posted December 7, 2015 Report Share Posted December 7, 2015 360-004 is one prong 0-150 also 10 bar Link to comment Share on other sites More sharing options...
FlyingMonkey Posted December 7, 2015 Author Report Share Posted December 7, 2015 360-004 is one prong 0-150 also Is the one prong just ungrounded, or does it ground against the body of the sender/threads...? Link to comment Share on other sites More sharing options...
procharger Posted December 7, 2015 Report Share Posted December 7, 2015 against threads I guess at least on my HKS engine I don't know if FD uses both or not Roger will know I am sure? Link to comment Share on other sites More sharing options...
FlyingMonkey Posted December 7, 2015 Author Report Share Posted December 7, 2015 The FD senders are the two prong type with a dedicated ground wire. EDIT: Now that I think about it, the factory sender under the gearbox area might be thread grounded. Link to comment Share on other sites More sharing options...
Tom Baker Posted December 7, 2015 Report Share Posted December 7, 2015 The one mounted to the oil pump is one wire grounding through the threads. This was standard Rotax. When mounting on the firewall you need two wires one for the instrument the other for ground. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted December 7, 2015 Author Report Share Posted December 7, 2015 Thanks Tom. Link to comment Share on other sites More sharing options...
Tom Baker Posted December 7, 2015 Report Share Posted December 7, 2015 I have bench tested sending units before using a compression tester. Someplace I found a chart of resistance to pressure for the switch. I posted it quite sometime ago. When bench testing I did find some senders that would read OK at the higher pressure settings and low in the normal operating range. That still wouldn't explain why your goes back to reading normal with the equipment turned off, unless like you said the higher voltage overcomes the change in resistance. Link to comment Share on other sites More sharing options...
FredG Posted December 8, 2015 Report Share Posted December 8, 2015 Andy, if I were troubleshooting this problem, I would try, at least temporarily, to verify the voltmeter readings. The change in voltage from avionics ON to avionics OFF and its reproducible effect on indicated pressure is compelling to me. The thing that I cannot figure out is why it was OK for a while and now it isn't (again). It is consistent with a change in the sender, but having several go bad in a couple of years is odd. Good luck, keep us posted. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted December 8, 2015 Author Report Share Posted December 8, 2015 I agree Fred, it's weird. If a quick sender change doesn't have immediate results, I am going to have to do some electrical troubleshooting for sure. Link to comment Share on other sites More sharing options...
Anticept Posted December 8, 2015 Report Share Posted December 8, 2015 We had these sensors going bad often too. That's why I took the time to rewire mine to accept the new slimmer style. Haven't had one fail yet. Anyways, none of this makes sense with the context provided, so I am going to disregard your previous replacements and consider this an incident of it's own, as that's the only way the effect of the avionics switch can even begin to make sense. I want you to get a voltmeter, and set to volt mode, and turn everything on in the plane that you can with engine running. Touch the grounded side of the indicator, and touch the negative battery terminal. If you read anything other than a fraction of a volt, you got a dirty ground that is only showing problems when enough amperage is pushing through it to cause voltage drop. There is one single bolt that goes through the firewall that everything grounds to, and thereafter all the way up to the battery could be the cause. The other thing to consider, is what another poster said in another thread: interference. That's a little more difficult to diagnose, as you will have to separate the wires from each other, or run some temporary jumpers. I'm trying to think of other tests. Did you save the old sensors? Link to comment Share on other sites More sharing options...
FlyingMonkey Posted December 8, 2015 Author Report Share Posted December 8, 2015 We had these sensors going bad often too. That's why I took the time to rewire mine to accept the new slimmer style. Haven't had one fail yet. Anyways, none of this makes sense with the context provided, so I am going to disregard your previous replacements and consider this an incident of it's own, as that's the only way the effect of the avionics switch can even begin to make sense. I want you to get a voltmeter, and set to volt mode, and turn everything on in the plane that you can with engine running. Touch the grounded side of the indicator, and touch the negative battery terminal. If you read anything other than a fraction of a volt, you got a dirty ground that is only showing problems when enough amperage is pushing through it to cause voltage drop. There is one single bolt that goes through the firewall that everything grounds to, and thereafter all the way up to the battery could be the cause. The other thing to consider, is what another poster said in another thread: interference. That's a little more difficult to diagnose, as you will have to separate the wires from each other, or run some temporary jumpers. I'm trying to think of other tests. Did you save the old sensors? Hey Corey... By "indicator" do you mean sender, or something else? I will check the voltage as you suggest. As I mentioned, I currently have a heavy gauge wire ground from the sender direct to the battery negative terminal, so I should have close to the same ground as I would see on a meter on the battery terminal. I think I still have one of the old senders. In any event I will have the current one once my mechanic and I remove it. Do you have a part number for the "slimmer style" sender? The one I ordered from Lockwood was a GAV360-430. It's possible I currently have a GAV360-410 in there now. When we relocated to the firewall, we did have to shave some of the rubber from inside the adel clamp...maybe that is because it was made for the smaller/newer sender? Link to comment Share on other sites More sharing options...
Anticept Posted December 8, 2015 Report Share Posted December 8, 2015 Indicator meaning instrument. Is the indicator electrically isolated from the other systems then? Or do you have two wires running from it (ground loop condition which will result in a lot of interference). Other thing to consider is positive power. I don't know how your gauge is wired, but either it is positive to sender to instrument to ground, or two legs go to instrument and then one or two goes to sender. If it is the latter case with only one wire, i want you to jumper the sender ground back to the instrument temporarily and let me know what happens. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted December 8, 2015 Author Report Share Posted December 8, 2015 Indicator meaning instrument. Is the indicator electrically isolated from the other systems then? Or do you have two wires running from it (ground loop condition which will result in a lot of interference). Other thing to consider is positive power. I don't know how your gauge is wired, but either it is positive to sender to instrument to ground, or two legs go to instrument and then one or two goes to sender. If it is the latter case with only one wire, i want you to jumper the sender ground back to the instrument temporarily and let me know what happens. Gotcha. There's a DB9 connector on the back of the gauge, and the sender, ground and power wire run through that. I will have to figure out which pins do what, which may take some wire tracing. EDIT: Here is UMA's "non-TSO instrument pinout" diagram...this may or may not be correct for my gauge: http://www.umainstruments.com/pdf/UMA_DB9-WIRING.t4g.pdf Link to comment Share on other sites More sharing options...
Anticept Posted December 8, 2015 Report Share Posted December 8, 2015 If you give me the instrument make and model, I can look up the manual for this part and tell you which pins go where. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.