Matt M Posted November 10, 2019 Report Share Posted November 10, 2019 (edited) Tonight while coming home from a trip on climbout the high lo vac annunciator light came on. My vac pressure gauge indicated 5” and I wasn’t worried because my primary instrument is an Aspen. It then intermittently flashed then went out. About 10 minutes later I noticed my oil pressure indicator dropped into the yellow, which really draws attention to you when it’s dark. I suspected something wrong with the gauge and continued on until I saw my oil temp gauge and CHT peg to the max. I also noticed the fuel pressure gauge fall slightly. Fuel gauges worked fine the whole time. I have an EDM 700 in the aircraft and none of the CHT readings from that were above 350 degrees, and oil was 179 degrees. It didn’t make any sense. My wife was watching the gauges and then smelled a burning smell which caused her to panic and we ultimately diverted. At one point I swear I saw the oil pressure gauge show 0, however I was focused on getting the plane on the ground. The engine ran fine the whole time, prop was staying at 2400 rpm and EDM never alarmed. After I landed I checked the oil and I had what I took off with and didn’t see any oil in the cowl. Left the plane at the shop to look at on Monday. It seems like all this is related to some sort of electrical issues since the transducers are in the vicinity of one another, with the fuel sending units being the only ones that were working. I bought the airplane in July and today was the also today is the first time I used the heat in the plane. Could a badly routed wire against something be a culprit? Any thoughts? BTW I have an 82 M20J. Edited November 10, 2019 by Matt M Forgot ac model Quote Link to comment Share on other sites More sharing options...
DonMuncy Posted November 10, 2019 Report Share Posted November 10, 2019 Check the ground to the cluster. Easiest way is to run a temporary new ground wire to a known good ground. 1 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted November 10, 2019 Report Share Posted November 10, 2019 Welcome aboard Matt. interesting first post. Waking up rested at home... taking things in from your post... 1) congrats on diverting, and getting on the ground... 2) The smell of burning stuff in the cockpit usually leaves some marks as well... 3) The thing that stands out to me most... are the ship's gauges misbehaving... 4) the OilT gauge is driven by a thermistor... temperature sensitive resistor... they typically fail benignly with lower and lower temps until they read zero... if a wire breaks, they read zero immediately... 5) to get an oilT reading to go off scale... it sounds like some electricity is being supplied to the system that doesn’t belong there... 6) be on the look out for evidence of a shorted wire... 7) any misbehaving circuit breakers? any popped out? 8) any work done behind the panel? Drilled holes, metal bits? 9) does the JPI data ever get downloaded? It keeps a record of the voltage supplied to it... that might be interesting to review... 10) Did you notice any funny amperage readings? Sometimes the naked shunt can be source of random power when something falls on it... PP thoughts only, not a mechanic... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
PT20J Posted November 10, 2019 Report Share Posted November 10, 2019 When multiple gauges act up, look for something they all have in common. Pressure gauges read zero when the sender wire is grounded; temperature gauges read full scale when the sender wire is grounded. So, I’d look for some place where multiple wires could be shorted to ground at the same time. I’d start inside the cluster gauge unit since it’s easy to get at. The heat from the cabin heater is not hot enough to damage the teflon-insulated wiring. If the heater hasn’t been used for a long time, I have had a smell come from it for a short time when first turned on - probably just dust in the ducts heating up. But it should dissipate quickly. It’s always a good idea to check the engine compartment for any signs of trouble whenever anything goes amiss with any sender located there - flammable fluids and hot gasses abound there. Skip 1 Quote Link to comment Share on other sites More sharing options...
PT20J Posted November 10, 2019 Report Share Posted November 10, 2019 Looking through the Mooney IPC and Service Manual, it seems that Mooney used several different gauge clusters and transducers over the years. The early models used temperature and pressure transducers that were a simple variable resistance to ground type. Later models used more accurate wheatstone bridge type transducers, and some apparently required external amplifiers. I've never had to delve into the internals of the cluster gauges and I don't know what your setup is. Perhaps @M20Doc might have further details. I'd still bet it's something within the cluster since you had issues with multiple gauges. It's possible there is a regulated voltage reference or something inside, but it's hard to tell since Mooney doesn't show any details of the internals. But if you take it apart and something blew enough to make a stink it will probably have left evidence behind. Skip Quote Link to comment Share on other sites More sharing options...
Matt M Posted November 10, 2019 Author Report Share Posted November 10, 2019 Thanks. It was very odd. I think if I didn’t have the engine analyzer I would have been more concerned. Still flying over the pine barrens of southern NJ when it’s dark is not something I want to do with odd engine indications. Now the airplane is an hour away from my home base so there is not much I can do to troubleshoot. I am at the mercy of the mechanic there. Quote Link to comment Share on other sites More sharing options...
carusoam Posted November 10, 2019 Report Share Posted November 10, 2019 Where did you leave the plane, Matt? We May know a few people in the area... might be able to help you get back and forth as well... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Matt M Posted November 10, 2019 Author Report Share Posted November 10, 2019 8 minutes ago, carusoam said: Where did you leave the plane, Matt? We May know a few people in the area... might be able to help you get back and forth as well... Best regards, -a- I left it at Ocean County. Need to give Oceanaire a call in the morning. Luckily the FBO was still open waiting for a jet to come in after hours, so we weren’t stuck out in the cold waiting for our ride. I am based out of Woodbine so it’s not bad to get there. 1 Quote Link to comment Share on other sites More sharing options...
Matt M Posted December 27, 2019 Author Report Share Posted December 27, 2019 (edited) So the verdict was a loose connection that came through the firewall for the engine gauges. They said there is a barrel connector and when they moved the connector they could replicate the problem. They sprayed contact cleaner and fixed the problem. Edited December 27, 2019 by Matt M 3 Quote Link to comment Share on other sites More sharing options...
carusoam Posted December 27, 2019 Report Share Posted December 27, 2019 Great follow-up, Matt! Best regards, -a- Quote Link to comment Share on other sites More sharing options...
PT20J Posted December 28, 2019 Report Share Posted December 28, 2019 Thanks for the follow up. So often we don’t get “the rest of the story” and don’t get to learn from other’s experiences. Skip Quote Link to comment Share on other sites More sharing options...
Matt M Posted December 3, 2020 Author Report Share Posted December 3, 2020 I went up tonight to get my night currency. On climb out I noticed my fuel pressure was lower than normal and then noticed my oil pressure was barely in the green and cht and oil temp were abnormally high. I had this same problem a year ago which caused a deviation to another airport. The shop investigated and determined it to be the cannon plug connector. They sprayed some contact cleaner and all was well. I picked the plane up and everything was good to go. Well what I didn’t test last year when I picked it up was turning the panel lights on. I didn’t put two and two together at the time that the panel lights were the cause. I haven’t used them since then. All my flying was during the day. When I turned them off tonight the gauges returned to normal. Turning the panel light rheostat brighter causes them to fluctuate. Pressure gauges go down, temp gauges up. Turn the lights off and all is well. Thoughts? Bad ground connection on the back of cluster gauge assembly? I will troubleshoot by hooking a temp ground wire to the back of the cluster panel and see if I can replicate problem. Matt Quote Link to comment Share on other sites More sharing options...
carusoam Posted December 3, 2020 Report Share Posted December 3, 2020 Hey Matt! Sounds like a grounding issues... If you have the challenge identified as the panel lights rheostat... the world of problems just got smaller... Certain ground wires have a tendency to go missing, break down, get loose, or suffer corrosion... Panel lights draining electrons to the panel may be interfering with electrons trying to escape from the other instruments... The panel itself may be mounted on rubber vibration dampers... so... it could be a rate of grounding issue... the engine, the air frame, and the instrument panel...all need to be connected together really well... Hopefully you can chase this without having to run the alternator... Do you have the wiring diagrams for your ship? These may help with finding where the usual grounds might be located... Might want to start with measuring resistances... or adding a wire from the panel to the airframe... just to test... PP thoughts only, not a mechanic... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
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