Ironflight

Ironflight

VAF Moderator / Line Boy
Mentor
OK folks, we had a great Christmas here at the "Mikey Upgrade Facility" (actually, we did Christmas things most of the day, took the Val up into a beautiful blue, calm, cool Texas sky for awhile...and THEN rolled Mikey out for his first start after the new panel install!), culminating in the first engine run. All went well except for a lack of oil pressure. Logic tells me that this engine was running perfectly when it rolled into the hangar, and we haven't touched a thing inside, so I KNOW it has oil pressure - but the Dynon D-180 is reading "zero", even after a three minute run which included some fast idling.

I took the 'ducer off the engine and connected it to the end of an air pressure hose, then slowly cranked up the pressure to 90 psi - the D-180 showed a maximum of 5 psi - so we know that "something" is happening. My theories are:

1) 'ducer is broken out of the box - unlikely, but possible
2) 'ducer has no oil in it, and doesn't react the same to air as it does to being filled with liquid.
3) Calibration error? There doesn't appear to be a calibration factor in the D-180 for this (the "type" is selected to "1" in the setup - it's the Dynon 'ducer)

Has anyone else got a theory, or experienced this problem? Since the 'ducer has a very tiny orifice I'm at a loss as to how to fill it with oil if that is the problem. I am going to put an analog gauge on the engine tomorrow to make absolutely certain it has oil pressure.

Paul
 
Hi Paul,

I believe the transducer needs a ground path if you are using the dynon transducer. If you can get a ground to the transducer somehow, it should work if thats the problem.
 
Ground

I've got that covered Tom - thanks for the suggestion. It doesn't have a separate ground lug like the fuel pressure sensor, and grounds through the case. Just in case, I put a separate ground to the airframe when I tested it and had no joy....

next?
 
HI Paul,
Hae you tried disconnecting the wire from the oil pressure transducer and measuring the resistance from ground to the terminal on the transducer with the engine stopped and the engine running? This will let you know if the transducer is working or not. You should see a big change in the resistance while running.
 
The problem I had two days ago with my D120 was a high reading. It would go from 75 psi. to over 98 psi. jumping back and forth. The grounds all seemed ok,( I had soldered a wire to a s.s. hose clamp and grounded the other end to the engine). All I did was loosen and re-tighten the hose clamp and the presure was 65psi. on next flight. These grounds need to be good.
Ron
 
Ironflight said:
SNIP
I am going to put an analog gauge on the engine tomorrow to make absolutely certain it has oil pressure.
Paul
Click to expand...

Paul, good idea (although I agree with you, it would be bizarre if something magically happened to the oil system).

The size of the orifice would only make the reading sluggish to change up or down if the transducer is filled with air.

I think bad/wrong transducer or some scale factor needing setting.

BTW, do think about what you would do in-flight if the electronic oil pressure system tells you your oil pressure just went to zero. This is the one and only engine parameter I have mechanically backed up. I've had cars with idiot lights come one only to find out the transducer conked out. Many on this forum have had erroneous oil pressure readings in flight with various systems. The 1" round UMA gauge is a simple insurance policy against that concern.
 
pump the line full of oil

Hi Paul,

Before I started the engine the first time, I removed the oil line at the transducer and cranked the engine til oil came out at the advice of a local. I did have good pressure from the first run.

Not sure from your initial post if you did that, but thought I would throw it out there.
 
Thanks for the additional ideas - I have been sitting here thinking about running a direct ground tomorrow to make sure that I have no resistance built up in the system. I also know that I have oil at the transducer, because I took it off and it is "wet", so I'm not to worried about that.

Alex has a very good point about having to trust the single measurement - and I don't In the Val, and in Mikey's new panel, I have an oil pressure switch to drive the panel light directly - but I seem to have lost the part number of the one I used in the Val, and the one I picked up for this application doesn't seem to be working right yet....and I intend to have THAT working before we fly. Oil Pressure is the one parameter I really need to know is there in a Lycoming - everything else can be inferred if the engine is running.

Paul
 
Paul, is it possible that the unit is reading bars? That would be close to being right. There is another thread discussing something similar.
 
Paul,

I did nothing special with my ground; just put it on the common ground block.

May I suggest you check your Dynon settings? Maybe make sure the oil pressure is turned on? Just a thought, although I don't remember doing more than setting the limits.

Good luck with it.
 
Not sure

Hi Clay,

The vdo is a mechanical unit that has no sender - not sure what you are asking. I have a Dynon sender - but don't know the specs on it.
 
Solved!

Well, this is embarrasing.....:eek:

Thanks for all the ideas folks, but this turned out to be a very simple wiring error on my part. I put in the new oil P sensor and oil P switch weeks ago, and ran a couple of white wires back to the firewall. Last week, when we installed the panel, I ran the sensor wires forward through the feedthroiughs and hooked them up. When I started troubleshooting today, I thought ":Hmmm...if I disconnect the oil P switch, the panel light should go out..." so I did - and it didn't! Dang - how bad a mess have I made of this? Then the light bulb went off (in my head) - I disconnected the wire from the pressure 'ducer, and bingo - the warning light went out.

Yup - had the two reversed - the discrete switch was feeding the Dynon, and the ''ducer was feeding the light - and that didn't work very well! Took 30 seconds to fix, and all is normal. BTW, the resistance between the panel ground and engine was about 1 Ohm (on a cheap DVM that I wouldn't trust to plus or minus a couple), but it was a good thing to check.

Bottom line on this was not to over-react to a bad 'ducer - I KNEW I had oil pressure because it didn't make sense no too....oh, and of course, check the wiring first!

Paul
 
petehowell said:
Hi Clay,

The vdo is a mechanical unit that has no sender - not sure what you are asking. I have a Dynon sender - but don't know the specs on it.
Click to expand...

The link you provide also has the VDO senders we get with the GRT stuff - it's just there are several to choose from, depending on the ohm range you need. I'm not sure what range I need, but I got my oil pressure figured out.
Thanks anyway.
 
Hey Paul,

You should be able to read the resistance of the sender to determine if it is working correctly. The following table is the resistive curve for our oil pressure sender:

Pressure (PSI) Sensor Ohms
0 9.5
5 18.6
10 25.5
15 32.4
20 37.8
25 45.1
30 50
35 56.9
40 64.7
45 70.9
50 77.3
55 84.5
60 91

With the engine off for a few hours, read from teh output to ground and see what reading you get. Remember that it may take some time for the pressure in the line to go down as everything drains back.

Then you can turn the engine on and see what reading you get.

Compare these reading to what the EMS is showing you.

Let me know if you are still having problems and we can move on to more in dept trouble shooting.

Also make sure you have sensor type 1 selected from teh setup menu MORE>SETUP>SENSORS>OIL PRESSURE

Let me know.

Eric
 
That table didn't come out right on my post above. The number on the left is the pressure and the number just to the right of that is the resistance value.....just in case you were looking at it funny. ;)
 
Thanks for the data Eric - that is a useful table for everyone. Of course, it helps if we hook the sensor up to the correct wire if we want it to work...(see my post above...)

Paul
 
VDO Oil Pressure Backup

Alex got to me from across the hangar - so I will be looking to install this manual Oil Pressure backup:

2000632695466732059_rs.jpg


Not lit - just a tubing connection to the the oil pressure manifold.

Need to figure out where on the panel it is going to go........
 
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