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Ongoing oil pressure indication errors


FlyingMonkey

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I have had intermittent oil pressure indication errors since I bought my CTSW. I have had the the sender replaced (twice), the sender moved to the firewall using the Lockwood kit, checked and tightened all grounds, added dual ground wires to the sender to different ground points, and most recently crimped a new ring terminal on the sender signal wire. Each time the problem seems to go away, then a couple of weeks later the pressure starts creeping down again.

 

Today in the pattern the pressure slowly dropped from 35psi (it was already a little lower than the normal 40-50psi) to less than 10psi and at one point almost zero. I landed immediately. On taxi the pressure came back up a few psi.

 

The big clue came when I switched off the avionics master...the oil pressure immediately came up to almost normal. I started playing with various switches. Every time I switched something off, the pressure would come up a little, when switching things on it would drop a little. None of the other engine gauges showed any changes. So it's definitely electrical, and isolated to oil pressure.

 

One weird thing I noticed was that increasing rpm would sometimes cause the pressure to slowly drop a little. It seems the alternator should put out more voltage and make the pressure read up a bit, but I don't really understand electrons. Maybe the electrical system putting out more RF noise?

 

So what's going on here?!? I have a space factory gauge and could swap it out, that's about the only thing I know to do at this point. I could replace the sender again, but twice seems like enough on that...

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What type of oil pressure instrument? Electronic or D'Arsonval?

 

You might have a bad regulator rectifier. The more you load it, the more it seems to aggravate indications.

 

Another thing to look at is the fact you lose indication all together. Do you have a bad instrument? Vibration can loosen connections, which will definitely amplify the effect of voltage swings as a bad connection acts like a high resistance ground.

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Hi Andy,

 

This is very indicative of a bad ground. You may have tightened a couple, but may have missed the one you need. A poor sender connection could also be to blame, but my money rides on a ground.

Right now the sender has two grounds, one directly to the battery with a AWG 10 wire. I didn't think you could get a better ground than going direct to the battery...

 

I will recheck all the grounds and put some solder on the sender wire terminal connection to ensure a good connection. If these two items fail, what's next? As I said, I have a spare factory gauge...maybe the ground connection in the gauge is bad?

 

Anticept, I have the small factory UMA a analog gauges, not an EMS. Crimping a new terminal on the sender wire fixed it for a couple of weeks, it was perfect. Maybe it really is as simple as it vibrating to a bad connection. A recrimp + solder and some heat shrink for wire support might be worth a try.

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Try this first; Put a separate ground wire to the gauge and check it. This was what was wrong with one I fixed 4 years ago. Took me a couple of hours to figure it out. The meter said it had a ground it was just not a good one. A poor ground even though it's there will cause this type of fluctuation.


 


It has to be one of these. A bad sender, a bad wire connection, a bad ground or a bad gauge. Just rule out each. You may need to start back at square one and touch and look at every component. It may be a PITA, but that may be the only way to find it. Don't take what you did before as an exemption and check it all.


 


One last thing to do is to put an inline pressure gauge in and run it.  I personally haven't seen or heard of a real engine pressure problem. It has always been the external issues listed above.


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It wouldn't hurt to clean the grounds on the avionics switch and any other grounds in the avionics wiring all the way to the battery. It may be that load has an intermittent poor ground and is trying to go to ground through the oil pressure system. Electrons don't care which way they flow, they simply go from high pressure to low pressure, to use a water analogy.

 

Maybe you said, but does the gauge fluctuation seem heat related, as in when components warm up? Does the oil pressure look OK right after starting up but as the avionics or other gets used does the problem start showing up? I don't mean when the engine gets warm, I mean the avionics.

 

You say you were in the pattern. Were you using the radio a lot? How about if you are out flying somewhere and not using the radio a lot - what happens to oil pressure?

 

I take your word that you've checked the oil pressure system wiring thoroughly, but is it conceivable that when you do this you're wiggling or moving other wiring that is the real problem and it seems to be fixed for a bit but not permanently?

 

I suppose while you're at it you could clean all the instrument grounds, but to find the right one I suppose you'd have to check them one at a time.

 

The above are offered as observations and suggestions. I'm not a trained or experienced vehicle electronics guy so take it for what it is worth. Those problems can surely be aggravating.

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Try this first; Put a separate ground wire to the gauge and check it. This was what was wrong with one I fixed 4 years ago. Took me a couple of hours to figure it out. The meter said it had a ground it was just not a good one. A poor ground even though it's there will cause this type of fluctuation.

 

It has to be one of these. A bad sender, a bad wire connection, a bad ground or a bad gauge. Just rule out each. You may need to start back at square one and touch and look at every component. It may be a PITA, but that may be the only way to find it. Don't take what you did before as an exemption and check it all.

 

One last thing to do is to put an inline pressure gauge in and run it.  I personally haven't seen or heard of a real engine pressure problem. It has always been the external issues listed above.

 

 

I think you are right.  I'm confident it's not an actual engine issue, but if it can't get this resolved I will go there.  

 

I'm going to put a better terminal connection on the sender wire first, that is easiest.  If that doesn't work I'll look into the gauge end and run the separate gauge ground as suggested.  Then replace the gauge, then the sender again.  After that I'd have to start getting more esoteric.

 

BTW, when I replaced the sender I used the VDO sender because it was cheaper...is there any advantage to using the more expensive Honeywell sender? 

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It wouldn't hurt to clean the grounds on the avionics switch and any other grounds in the avionics wiring all the way to the battery. It may be that load has an intermittent poor ground and is trying to go to ground through the oil pressure system. Electrons don't care which way they flow, they simply go from high pressure to low pressure, to use a water analogy.

 

Maybe you said, but does the gauge fluctuation seem heat related, as in when components warm up? Does the oil pressure look OK right after starting up but as the avionics or other gets used does the problem start showing up? I don't mean when the engine gets warm, I mean the avionics.

 

You say you were in the pattern. Were you using the radio a lot? How about if you are out flying somewhere and not using the radio a lot - what happens to oil pressure?

 

I take your word that you've checked the oil pressure system wiring thoroughly, but is it conceivable that when you do this you're wiggling or moving other wiring that is the real problem and it seems to be fixed for a bit but not permanently?

 

I suppose while you're at it you could clean all the instrument grounds, but to find the right one I suppose you'd have to check them one at a time.

 

The above are offered as observations and suggestions. I'm not a trained or experienced vehicle electronics guy so take it for what it is worth. Those problems can surely be aggravating.

 

Jim, pressure does not seem to be a problem at startup, it's always 70+ immediately and then comes down over time.  Once the engine is warmed up a few minutes the pressure will settle.  If it settles over 40psi it will be fine the rest of the flight, but if it comes down to around 30psi I know that it will probably continue to degrade if i go fly.

 

I will admit that when we crimped the terminal on the sender wire last time we were rushed and used a lesser quality terminal because it was close at hand.  I think doing that over again and getting it really solid is a good place to start.  If that doesn't cure things I will take your suggestion and check all the connections I can lay my hands on.

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You seem to have a connection somewhere that degrades under some circumstances as it gets warm. I'd look at anything that warms up differently from flight to flight, and that might include the avionics system if you fly 80 miles one day and never touch the radio and stay in the pattern another day announcing every leg. You got to quit talking in the pattern. :)

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You seem to have a connection somewhere that degrades under some circumstances as it gets warm. I'd look at anything that warms up differently from flight to flight, and that might include the avionics system if you fly 80 miles one day and never touch the radio and stay in the pattern another day announcing every leg. You got to quit talking in the pattern. :)

 

Maybe I'll just turn off the radio to be safe.  ;)

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Ground

This is what i got a couple weeks ago.  The gauges were fluctuating quite alot so i was prepared for a gauge malfunction issue rather than an emergency one.  Sadly this happens alot on my CTSW but i gotta check the grounds and clean the terminal more often.

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This is what i got a couple weeks ago. The gauges were fluctuating quite alot so i was prepared for a gauge malfunction issue rather than an emergency one. Sadly this happens alot on my CTSW but i gotta check the grounds and clean the terminal more often.

That's exactly what mine looked like two days ago. It's very annoying. I know it's not a real pressure problem, but if I ever developed a real oil pressure issue, it would be masked by this ongoing issue.

 

EDIT: I didn't notice ALL your gauges are whacked. My oil pressure looks just like yours, and all my other gauges look perfectly normal.

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By the way, this discussion seem to me to be a good reason to have a sophisticated logging system in one's airplane. That way, one could hopefully analyze data and make correlations where they are logical. I hope the SkyView when I get it put in does that for me.

It has it, as long as data logging is on.

 

The D series also has data logging.

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If you have more than one gauge fluctuating it is absolutely a ground. You have one loose and need to find it.

 

Every thing my be hand tight, but wrench loose. Put a wrench on every ground. You have 5 main ones to put a wrench on.

 

I also see fluctuations from more than one gauge at the same time.  I had a mechanic install the extra ground wire from the battery to the engine.  That has not helped.  I just recently checked the four bolts that go through the firewall on the copilot's side and they are wrench tight.  I have found them loose in the past...but not last time.  

 

My question is how do I tighten the bolt that goes into the instrument panel...?  It seems very difficult to reach from the engine side.  From the panel side, there are so many wires using that bolt making that awkward as well.  I have requested that it be tightened during my last two annual inspections with no apparent improvement.  The mechanics are Rotax trained, but have very, very little CT experience.

 

Thanks in advance...!

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All that needs to be done is to have someone hold the nut in the engine compartment on the main ground wire while someone inside tightens the main screw on the inside. I usually loosen the top nut on all the ground wires so I can get to the one in the back. The LS is just a tad different, but close enough to do almost the same thing. The SW has a screw with all the ground wires piled on top and the LS has a ground block plate with lots of spade connectors on it from each wire. 

Since you have a new ground wire from the battery to the engine now run that same wire into the instrument panel and place it on the main ground screw. See this post and pictures under the maint. section.

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And the apparent winner is:  faulty oil pressure gauge!

 

After re-terminating the sender wire, we started it up and taxied around.  We knew immediately that the problem was not solved; the pressure continued to fluctuate with changes in system electrical load, and quickly dropped to 30psi.  As we taxied it went to 25psi, and we taxied back and shut down.

 

Luckily, I have a complete spare set of analog factory engine gauges, that came out of Bill Ince's CTSW when he upgraded to his Skyview panel.  He threw them into the deal when I bought his autopilot (thanks Bill!).  So we swapped out the gauge, which was four screws and a DB9 connector, it took two minutes.

 

As soon as the pressure came up on start up, I knew the gauge was the problem.  My old gauge on start up would sweep quickly up to 70-80psi, then settle very slowly over a minute or two to 50psi.  The replacement gauge had the pressure come up more slowly, but it went to 50...and stopped.  Completely different behavior.  It then stayed at 45-60psi for over an hour of flying, with the engine at everything from near idle to flat out WOT.  It was very consistent, and did something my old gauge never did...occasionally went *up* from the baseline pressure.  The first time I saw it go from 45psi to 55psi in flight, I knew the problem has been resolved.

 

I'm pretty sure this is going to end it, but I have been sure before too...

 

So the only remaining problem is that my old gauge has a built-in lighting ring for night time, and the new gauge does not.  Not the end of the world to have one gauge not light up, but it annoys my sense of order.  Does anybody know if it would be economical to have the old gauge repaired?  I'm going to call UMA tomorrow and ask about it.  If not, maybe they will switch the light ring to the replacement gauge for a nominal fee...

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So the only remaining problem is that my old gauge has a built-in lighting ring for night time, and the new gauge does not.  Not the end of the world to have one gauge not light up, but it annoys my sense of order.  Does anybody know if it would be economical to have the old gauge repaired?  I'm going to call UMA tomorrow and ask about it.  If not, maybe they will switch the light ring to the replacement gauge for a nominal fee...

 

Is the ring inside, or outside, of the gauge? If it is outside, you can transfer them legally. If it's integrated into the gauge, they will only overhaul. No instrument company does anything to gauges and instruments anymore without overhauling, due to too much liability.

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