S3flyer Posted June 9, 2012 Report Share Posted June 9, 2012 Of course, my VDO oil pressure sender got jealous with the attention I giving the fuel pressure sender issues. It failed with the typical symptoms but I have a couple spares in the hangar and promptly replaced. Oil pressure read slightly higher (mid-50s versus high-40s) with the new VDO sender but were solid for my first 1.3 hr flight. Fired up the plane a week later, oil pressure reading OK and steady on run-up. Took off, left the pattern and 15 minutes into flight, the oil pressure went up to about 75, then slowly down to 55 and bounced around 55-75 as I hung a U-turn back to the airport. Did a little trouble shooting today and I'm 99.8% certain it's the sender (again). 1.6hrs to failure has to be a new record :mad: Link to comment Share on other sites More sharing options...
Roger Lee Posted June 9, 2012 Report Share Posted June 9, 2012 That symptom can be either air in a remote mount setup for the oil sender and will work its way out or my bet is on a poor incomplete ground. Yes it is possible to have an out of the box bad sender. I was having an issue with oil temps bouncing 20F. I knew it was poor grounding so I took a #4 wire from the engine just under the carb drip tray screw and right to the battery. The oil temp no moves around 5F and is lower. Now to test a little more I'm going to run another wire from the carb drip tray screw where the other ground is and straight into the instrument panel and onto my ground screw. This will bypass all the ground wires that go every where else and just bolt under other items. I'll do this tomorrow and let people know. This should give me a direct ground for everything right to the battery and loose all the other cables that are causing resistance. Link to comment Share on other sites More sharing options...
S3flyer Posted June 9, 2012 Author Report Share Posted June 9, 2012 Don't have the remote mount. Could air in the system still be a possibility and, if so, any guessing on how long it may take to work itself out (an hour flight or two). Link to comment Share on other sites More sharing options...
Roger Lee Posted June 9, 2012 Report Share Posted June 9, 2012 If it is mounted on the engine then it isn't air. It can be a ground or a bad wire connection where the wire is crimped onto the connector on the sender. I would also highly recommend you tighten all the grounds in the engine compartment and the one in the instrument panel before you go an do anything else. They are hand tight and wrench loose until proven otherwise. By the way, does the pressure change with adding and subtracting throttle? If it does then it is a loose ground or loose connector. Link to comment Share on other sites More sharing options...
Runtoeat Posted June 9, 2012 Report Share Posted June 9, 2012 Roger, you say if oil pressure changes with changes to throttle, then it is probably a loose connector or bad ground. I'm familiar with most engines showing lower oil pressure at low rpm's than at higher rpm's. Should one expect to see the Rotax oil pressure remain pretty constant, no matter what the engine speed might be? Side note - my oil pressure runs just into the yellow which is around 25psi. Due to this, I temporarily installed a mechanical pressure gage at the turbo oil port on the face of the oil pump plate. The mechanical gage reads 20psi higher than my panel gage. I suspect my sender is bad. Link to comment Share on other sites More sharing options...
Safety Officer Posted June 10, 2012 Report Share Posted June 10, 2012 Hi Dick, What I think he is trying to say is if the oil pressure is around let's say 50 psi while at idle and then you advance the throttle and the farther you advance the throttle the lower the pressure goes and it may go down to 20 psi and when you pull back to idle the pressure comes back up to 50 psi. That is a bad ground because our temps and especially our EGT and CHT probes work on mili volts and the slightest resistance change to the ground changes their readings. Poor grounds and connections cause big changes and usually not just a few psi or F. If you have a low reading all the time or only a 3-5 drop then it probably is the sender. If the temp or psi pegs out high then you lost the connection. The first start oil pressure on the Rotax is usually higher than it is after it warms up. Mine is around 63 psi on start then drops to 54 after warm up. My bet is your sender is bad. Link to comment Share on other sites More sharing options...
Runtoeat Posted June 11, 2012 Report Share Posted June 11, 2012 Hi Roger, your explaination helps me do some trouble shooting. A rise in pressure is seen when backing off the throttle so I'll recheck my grounds which I haven't done lately. My oil pressure is in high 20's and low 30's most of the time while at cruise. My quick look-see with the mechanical gage showed that the panel gage was reading about 20psi low. Due to squirting oil from poor temporary fittings, the test was ended without giving it a good try. I'm going to go back and install the mechanical gage with good fittings this time and see what's what. I'm thinking same as you - suspect a sender not working right but will look at my grounding. Link to comment Share on other sites More sharing options...
Roger Lee Posted June 11, 2012 Report Share Posted June 11, 2012 I'm with the Safety Officer. The sender is most likely bad. Link to comment Share on other sites More sharing options...
Runtoeat Posted June 11, 2012 Report Share Posted June 11, 2012 Woof........woof! (Just sharing a joke with the Safety Officer.) Link to comment Share on other sites More sharing options...
S3flyer Posted June 11, 2012 Author Report Share Posted June 11, 2012 Given the failure possibility of the sender, I'm considering permanently installing 1.25 inch mechanical gauge as a backup. Anyone done this? Link to comment Share on other sites More sharing options...
Roger Lee Posted June 11, 2012 Report Share Posted June 11, 2012 Everyone will find that the senders have varying life spans for sure, but you will usually get good life out of them if you remote mount the oil and fuel pressure senders to the fire wall to help cut vibration. Then wrap them in a piece of fire sleeve to help insulate them from some of the heat. Wrapping the exhaust pipes in the header wrap cloth will also help surrounding parts like senders, wiring and hose survive heat issues. Link to comment Share on other sites More sharing options...
S3flyer Posted June 13, 2012 Author Report Share Posted June 13, 2012 Went out to continue debugging the oil pressure issue but this time brought someone with a clue -- my mechanic My mechanic and Roger also spoke on the phone for a bit -- thanks, Roger! My Sting has about 5 grounds and we checked all possible combinations with good readings for all. We then loosened, cleaned and rechecked the grounds -- all good. We checked the sender wire and all seems good there. The sender behavior still was as described above, though. We replaced the sender, did the runup and my mechanic actually pulled on the wire while the engine was going to see if that caused any fluctuations. Steady as a rock, well maybe moved a PSI or two but it was hard to correlate to the pulling. Flew around the patch for 30 minutes and the oil pressure seems OK. Idle is in the mid-50s for a warm engine and cruise is in the mid-high 40s. I am probably going to run another ground just for the heck of it at my next oil change. Link to comment Share on other sites More sharing options...
Roger Lee Posted June 13, 2012 Report Share Posted June 13, 2012 Hi Dave, So your problem is fixed? Do you think cleaning and tightening the grounds did the trick? Link to comment Share on other sites More sharing options...
S3flyer Posted June 13, 2012 Author Report Share Posted June 13, 2012 I'm not declaring victory yet. I do believe the grounds were, at least, part of the issue. Cleaning the grounds has also bumped up the fuel pressure about 0.2 PSI so this indicates there was an issue there. I'm going to give it a couple more flight hours and report back. Link to comment Share on other sites More sharing options...
airhound Posted June 17, 2012 Report Share Posted June 17, 2012 Hi, mi Honeywell had been vasilating 20pts and now it spikes to the left to 0 and then rapidly builds back to 50ties. I checked all firewall side grounds with a screw driver and didn't notice any looseness and just short of disassembling, cleaning, with just 60 hours on the 2 year old configuration I was thinking about adding, if I understand your previous posts a " #4 wire from carb drip pan mounting bolt to a major ground/battery neg post". What does that do to settle thinds down? Oh and my sensor was moved 10 hours ago from engine to engine mount and never really was rock steady. What ground is there inside the panel, if any? I'm in a RANS S-19 with Dynons. Thanks for any ideas? Link to comment Share on other sites More sharing options...
Roger Lee Posted June 17, 2012 Report Share Posted June 17, 2012 Hi Doug, I just experimented with this setup in my CT and it did make a difference. Many of these bouncing temps and pressures are ground issues, but sometimes they can be just a bad sensor. To check the ground issue, use a #6 wire right from the engine closet to the battery and connect it to the battery negative. Then from the same connection on the engine or battery run another #6 wire in to the ground block. Then go fly. If the problem goes away then its a bad ground setup, loose wire, corrosion or just loose grounds. If the problem persist then it may be prudent to change the sensor. Link to comment Share on other sites More sharing options...
Jim Meade Posted June 17, 2012 Report Share Posted June 17, 2012 What do these sensors cost - $180 or so? I'll switch if convinced it is useful, but kind of hate to switch at that price range just willy nilly. Oh, well, I have a CHT rading that is bad and I will do the ground stuff but may have to do the sensor. Roger - I asked in another thread if you had any details on the LS ground buss - I'd like to know more so I could think of putting one on my SW. You and others have convinced me that plattic airplanes are asking for ground problems. Not having done a switch, I assume the sensor is right in the stream of the subject fluid? That the CHT is in the water jacket? The reason I'm asking is because I want to know if I can just swap a couple of sensors of if I need to drain some fluids, etc., first, which probably would cause me to just buy a spare and swap that way. Link to comment Share on other sites More sharing options...
Roger Lee Posted June 17, 2012 Report Share Posted June 17, 2012 The CHT and the oil temp probe are identical. If you get them from Rotax they are about $180 (ridiculous), but they rarely ever go bad. You can buy these from a different source and get them for a lot lot lot less. These are very dependable probes and are good 98% of the time. The CHT only reads metal temp and does not insert into any coolant. It is a blind hole. The oil temp probe will leak oil if taken out. The LS ground buss won't make any difference over the SW screw as it is just a different way to tie wires to the ground system. All the grounding is the same on the CT's except for just the final ground screw or buss. The thing to do is make the grounds better, changing the buss verses the screw won't make any difference. Enhance the grounds with a more direct wire. Leave the FD ground wires in place. I would leave the probes in place, just fix the ground. Link to comment Share on other sites More sharing options...
Jim Meade Posted June 17, 2012 Report Share Posted June 17, 2012 I assume that neither heat transfer paste nor electrical conducitivity grease would help the sensors provide stabile readings? I'll have to go in and take a hard look at how things are wired. Better grounding is a no brainer, of course. Link to comment Share on other sites More sharing options...
airhound Posted June 24, 2012 Report Share Posted June 24, 2012 Hi Doug, I just experimented with this setup in my CT and it did make a difference. Many of these bouncing temps and pressures are ground issues, but sometimes they can be just a bad sensor. To check the ground issue, use a #6 wire right from the engine closet to the battery and connect it to the battery negative. Then from the same connection on the engine or battery run another #6 wire in to the ground block. Then go fly. If the problem goes away then its a bad ground setup, loose wire, corrosion or just loose grounds. If the problem persist then it may be prudent to change the sensor. Roger, I have a Rans, S-19....but generally what does the ground block look like.....Brass or Copper strip on the engine firewall side located the shortest distance to the starter? So, i guess disconnect the battery ground and slip the 6ga wire on as described above. If it works it should stop the gas and oli pressure gages from bouncing, is that it? and how much are the honey well oil pressure sensors? I put a new fuel pressure sensor on, which now will read 5.8 thru 6.3.....I subtract the resting reading (1.2) from the sensor and that makes those numbers come down in the green...., I subtract 1.2 from 6.3 = 5.1.........is my thinking OK here? Doug in IL :blink: . Link to comment Share on other sites More sharing options...
Roger Lee Posted June 25, 2012 Report Share Posted June 25, 2012 Hi Doug, The fuel pressure may be bouncing if you don't have a fuel pressure dampener in line like the CT's with a Dynon. If you do have a dampener it could be the ground for this too. The ground block could be a couple of screws with a bunch of white wires on them or a long wide block with all the wires attached with spade connectors. Color won't be a determining factor. It depends on how your plane was set up. The idea is to get he most direct route right to the grounds from the battery. Yours may already be that way, you need to look. FD's takes the long route and looses a little connectivity. Honeywell sensors aren't cheap, about $258. You can and should remote mount your fuel and oil pressure senders and that will help keep the vibration away and mount them very low on the firewall in the cowl where it may be a little cooler. It will just help with their longevity. A new fuel pressure sensor should not have a "resting" pressure unless you have already run the engine or it has been out in the heat for a long time to build a little vapor pressure. Are you using a Dynon panel? Link to comment Share on other sites More sharing options...
airhound Posted June 25, 2012 Report Share Posted June 25, 2012 No fuel pressure sensor damper. Should I get one from Leading Edge or Spruce? Neg block, I think I have two rows of spade ended wires, so to I screw the 6 ga wire on an empty space? I remoted the sensor aft and lower on the engine mount with the MFGs kit....Not sure why after that it would be spiking to 0, Then building back up to 50-60 psi. The fuel sensor is and the fuel pump are new.....mounted on the cross over tube between carbs. But, the tube has rubber ends, so there is shock absorbtion. So, its hot all the time here know, would that impact the resting pressure reading.....What happens if you operate with legit high pressure? Thanks! :wacko: Roger Link to comment Share on other sites More sharing options...
Roger Lee Posted June 25, 2012 Report Share Posted June 25, 2012 Hi Doug, Take the oil and or the fuel sender off the engine and engine mount completely and put them on the firewall. FD had the fuel pressure sender on the crossover tube , too. They moved it because the heat and vibration were killing them. remote mount it on the firewall in fire sleeve. Then place a cut open piece of fire sleeve wrap around the sender itself to help insulate it from the heat. Mount the sender slightly above the cross over tube. Mounting it low down on the firewall causes the 91 oct. fuel to just sit there stale and cook in the heat. It will go bad and start to clog the sender hole. It can be cleaned out sometimes, but needs to be removed and the old fuel drained out of the hose hanging down. Mounting it up above the cross over tube slightly always keeps fresher fuel in the line. I remounted mine 4 years ago up higher and have never had an issue since. The Flowscan dampener goes in the upstream fuel line just before it enters the pump and not in the out line to the crossover tube. http://www.floscan.com/html/blue/accessorydetail.php?aid=98 If you truly have high pressure and the carbs can't hold it back it will cause rough running and fuel will probably come out the carb vent tubes. Put the ground wire under any terminal screw that connects all the grounds. Link to comment Share on other sites More sharing options...
S3flyer Posted June 30, 2012 Author Report Share Posted June 30, 2012 Thought I'd report back on my oil and fuel pressure issues. First oil pressure, I do believe that the replacement sender was bad and this particular failure was not related to the grounds. My fuel pressure sender (westach, not VDO) issue of minor trending down then moving back up was the connection. Link to comment Share on other sites More sharing options...
airhound Posted August 25, 2012 Report Share Posted August 25, 2012 Rog and all, My fuel and oil sensors went bad due to vibration and heat/location....on the engine. Now that I have them off the engine they seem to acting to specs. One more thing I will do is wrap the exhausts...Rather than asking you to repeat for the umpteenth time on the technique and material to use would please direct me to that string...? Thanks Doug Link to comment Share on other sites More sharing options...
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