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  #1  
Old 05-19-2019, 08:09 AM
chepburn's Avatar
chepburn chepburn is offline
 
Join Date: Apr 2006
Location: Ottawa , Canada
Posts: 235
Exclamation Need Help diagnosing Oil Pressure Issue

Hello,

This is a long post..... but PLEASE read it, and if you have some ideas on what might be happening ...we would appreciate the feedback

We have been trying to diagnose an oil pressure issue for the last few weeks that shows up as fluctuating oil pressures.

The first chart shows the oil pressure and oil temperature during the first event. The response of the oil temperature moving in lock step with pressure had us a bit puzzled..how much lag should there be? and worried at the same time.

We replaced the VDO sensor to see if that was the issue and flew again.


Here is the plot of OilP and Temp on the first event flight:




After replacing the VDO and taking a short flight
Pressures seemed normal:




Thinking all was OK, we took the airplane the following weekend, and all was operating normally, until ALL engine parameters went INOP at the EFIS.

That is definitely a data signal issue from the RDAC to the EFIS. We pulled the data link wire and inspected the connection, and found a significant loss of strands at the screw in connector at the back of the EFIS. Refinished the ends, laced the data wire in more places, and reinstalled.

That brings us to yesterday for the next test flight.

I was doing a local short flight near the airport to check things out again. Everything seemed nominal, until about ten minutes in, where I noticed that instead of a normal 85PSI at 23 inches/ 2400 I was at 60 PSI.
HMM. Something is up, so I executed a return to base to investigate.

The Top set of plots are oil pressure and Temp, Manifold pressure, and CHTS during this last flight.

I have also included a set of plots from last year in May, showing nominal for comparison.

After the flight, I added a mechanical pressure gauge and ran the engine up on the ground to 17MP and 1900 RPM. Oil pressure on the EFIS and the mechanical matched at 90 PSI, and I let the oil temps get to 120. (so not very hot yet)


Now the big question (s) ::::
What is happening?
IS there an impending BAD failure coming?
Could this be caused by a bad vernatherm?
Have we already damaged our engine?
Could it all be an electrical issue?




Oil Pressure and Temp problem




Manifold Pressure during oil pressure event


CHT during Oil pressure event



Oil Pressure and Temp Normal




Manifold Pressure Normal


CHT Normal
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  #2  
Old 05-19-2019, 08:43 AM
pilot2512 pilot2512 is offline
 
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Not an engine guy but I am an avionics guy. I would look at your grounds especially firewall forward.
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  #3  
Old 05-19-2019, 04:05 PM
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airguy airguy is offline
 
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Quote:
Originally Posted by pilot2512 View Post
Not an engine guy but I am an avionics guy. I would look at your grounds especially firewall forward.
Agreed - the way the pressure/temperature reflect each other so well on short time scales is highly suspicious. For one thing I don't think it would be possible, even with significant auxiliary equipment added, to get the oil temperature to legitimately vary that quickly. You've got some type of electrical issue going on with the sensing of the signals.
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  #4  
Old 05-20-2019, 05:00 AM
Tooch Tooch is offline
 
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Default sensor

I had the same problem. It was my pressure sensor.
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  #5  
Old 05-20-2019, 05:54 AM
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ColoRv ColoRv is offline
 
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Avionics. Check grounds. Check correct sensor is selected in setup.
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  #6  
Old 05-20-2019, 06:03 AM
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chepburn chepburn is offline
 
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Thanks for the input. So far the vote is electrical. I'd like to hear from some of the engine gurus on this site before we commit to another test flight.

From feedback here and knowledgeable people here at our airport the general consensus is electrical. We have checked ground paths and so far, no luck there. We are going to focus a closer look at the RDAC.

We had replaced the sensor for the latest flight, and the new sensor also shows noise...but beyond the noise the trend was downwards (to an alarming degree) So, if there is a blockage, or some other real oil pressure problem, we run the risk of very bad things happening if we decide to test fly to isolate the problem... or even high power extended runups.

General advice has been to eliminate the RDAC/EFIS path by wiring in a second indicator (either a pressure gauge or ohmmeter to read in the cockpit from a second port.

Go fly above the airport and wait for another event and compare the two indicators.

We are prepared to do this unless one of the engine guys on this site says:

NO!!! Check A and B first.....
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  #7  
Old 05-20-2019, 07:07 AM
vic syracuse vic syracuse is offline
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The safest thing to do would to temporarily place a direct-reading oil pressure gauge on it to compare the 2. Somebody at the airport should have one. If not, the local auto parts store will have one.

Vic
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  #8  
Old 05-20-2019, 07:52 AM
TS Flightlines TS Flightlines is offline
 
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I'd definitely plumb in a 'known good' mechanical gauge to verify the EFIS readings. I say 'known good' just because its a mechanical gauge doens mean its accurate. When the EFIS pressures begin to fluxuate, check the mechanical gauge. If that guage maintains its normal readings, then electrical gremlins are present. From what our avionics buddies tell us, it normally a grounding issue.

BUT test it---your plane is different than anyone else's.
Tom
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  #9  
Old 05-20-2019, 08:13 AM
BillL BillL is offline
 
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Quote:
Originally Posted by vic syracuse View Post
The safest thing to do would to temporarily place a direct-reading oil pressure gauge on it to compare the 2. Somebody at the airport should have one. If not, the local auto parts store will have one.

Vic
Absolutely !!!

I would not operate or fly the plane without a mechanical gage. You must prove it is not an oil system issue. Ground check first, do anything you can to safely get the temps up and check for deviation between the gages.

Data wise is it better to plot RPM vs O-Pressure than MAP. It will tell more about the oil system that way.

The oil pump is fixed displacement per rev, so pressure will rise with rpm until the relief is open.

Make sure your oil level is not excessive, we don't want excessive aeration of the oil. That will drop the pressure/speed curve. Easy to eliminate cold on the ground.
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