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Pegged Oil Pressure and No RPM

Gsuit

Gsuit

Well Known Member
I'm chasing two gremlins and hope the vast knowledge on this forum can help me catch 'em...

For information my setup particulars are:

- Superior XP-360 engine
- MT 3-blade propeller (MTV-12)
- LightSpeed Plasma III ignition (red box, not the Plus) with Direct Crank Sensor

No RPM
During my first engine start I had no RPM indication on the EIS. After speaking with GRT I performed the mod on the EIS as they prescribed where resistor R22 and capacitor 103 are snipped / removed. However, this did not fix my RPM problem. I continue to read 0 on the EIS display. To reiterate, the symptoms of my problem are:

- RPM reads 0 with or without the engine running
- I've changed the Tach P/R to 1, 2, and 3 with no change (engine and electrical system were completely powered down between Tach P/R changes)

No Oil Pressure
My EIS reads 0 for oil pressure, as it should, before engine start or any engine revolution whatsoever. As the engine rotates (either for actual start-up, or just to operate the prop/engine with no spark) the oil pressure begins to climb. Quickly it passes through 30, 50, 80... and if the engine is allowed to crank, will hit 99 and peg there. Upon engine shutdown, oil pressure will eventually subside back down through the numbers to 0.
So far, I have taken the following action:

- Verified oil actually pumping to the sender by removing the hose and rotating engine until oil pumped out of hose into can
- Verified the oil pressure sender is VDO and stamped "0-5 bar"
- Verified the sender has a good ground, good wire continuity, and good signal by powering the EIS and touching the orange/black oil pressure wire to the sender body (EIS reads 0). Also I have verified a good ground with a meter.

I have a call in to GRT and have emailed them, but expect they are down for Christmas. I'm itchin to get this fixed so I can move on... hoping for a January DAR visit :D Any help or troubleshooting advice you can give would be appreciated.
 
Oil pressure issue..

Clay, cant address the RPM issue but the oil pressure.. Have you tried 1. putting a typical analog gage on the system to see what the engine pump is actually putting out; or 2. borrowing the same sending unit from a good friend that is showing proper indications to verify the condition of your sending unit. If the same good friend is willing, put your sending unit into their engine and see if it does the same thing.
If everything is kosher with your unit in his engine, I'd look at a voltage issue from the EIS side..:confused:
 
Maybe this won't help, depending on what sort of connectors are involved...

I had lots of intermittent trouble with my *fuel* pressure sender -- after MUCH debugging, it turned out to be that the faston tabs on the sender were a little bit thinner than spec, and became slightly loose when they got up to FWF temperatures. The resistances involved are very small, so even a slightly loose connection will cause erratic readings.

A drop of solder on each faston solved the problem.
 
How long have you run the engine for? The EIS will not read oil pressures above 99 lbs, but it is not uncommon for oil pressures to be at or slightly above this at engine start. Once things start warming up, the oil pressure will gradually decrease.

erich
 
Mel said:
Be careful using this method of repair. Solder is very soft and will eventually wear down and the problem will return.
Click to expand...

Do you have a better alternative in mind? I replaced the crimped fastons (even using expensive AMP models) several times and the problem continued. Soldering them was the only thing that resolved it.

Fortunately, I can secure the wires nearby so there shouldn't be much vibration.
 
....replies so far.

Thanks for jumping in on this with me, so far. Here's what I've got today -

Radomir said:
which rpm source are you using on the LSE? (which pin and off of which connector)
Click to expand...

My cable from the direct crank sensor had the D-sub installed by the avionics shop that built my wiring harness for my panel. I've been presuming it is "as spec-ed" in the Lightspeed drawing (Analog Tach RPM, pin 2). How can I verify this?

erich weaver said:
How long have you run the engine for? The EIS will not read oil pressures above 99 lbs, but it is not uncommon for oil pressures to be at or slightly above this at engine start. Once things start warming up, the oil pressure will gradually decrease.
erich
Click to expand...

I was thinking along these lines as well. After another study in one of the three operation manuals I got at Superior, I found the Oil Pressure Operating limits to read:
Normal Operating Limits 50-95 psi
Normal Idle 20 psi
Start / Warm-up 115 psi

I've got a mechanical oil pressure gauge I'm going to install tomorrow and see. I'll post back.
 
Gsuit said:
My cable from the direct crank sensor had the D-sub installed by the avionics shop that built my wiring harness for my panel. I've been presuming it is "as spec-ed" in the Lightspeed drawing (Analog Tach RPM, pin 2). How can I verify this?
Click to expand...


I believe this is the problem... IIRC you should be using Pin 6 on Input connector... ("Signal to Electronic Tach"). There's more discussion about this on the Yahoo group -- if you search you'll find some hits. The takeaway is that LSE has 2 places to pick up tach signal (electronic on pin 6 of Input connector, and analog on pin 2 of Output connector)..

Though you may be able to make this work with some pull-up voltage (kinda the way fuel pressure etc is done).
 
Last edited:
I know this sounds wierd but are you getting good manifold pressure readings? I have seen incorrectly wired MP sensors throw off RPM and Oil. Just a suggestion.
 
Here's your problem with the Tach. The output you are using is for LS tach. The output that you want to use is PIN #6 OF THE INPUT CONNECTOR (same plug as the power leads are on).
As for the oil pressure are you using the right sender? GRT sends two senders one for oil pressure and one for fuel pressure. The lower pressure sender is for the fuel and the higher one for the oil pressure. THE OIL PRESSURE SENDER IS 0-20 BAR. The 0-5 Bar is for the fuel pressure. Make these changes and all should be good.

Have a merry Christmas.
 
Radomir said:
I believe this is the problem... IIRC you should be using Pin 6 on Input connector... ("Signal to Electronic Tach"). There's more discussion about this on the Yahoo group -- if you search you'll find some hits. The takeaway is that LSE has 2 places to pick up tach signal (electronic on pin 6 of Input connector, and analog on pin 2 of Output connector).. Though you may be able to make this work with some pull-up voltage (kinda the way fuel pressure etc is done).
Click to expand...

So, the correct connection for EIS is Pin#6 of the Input Connector? If I do this will I still have to use a pull-up resistor?

Rick S. said:
I know this sounds wierd but are you getting good manifold pressure readings? I have seen incorrectly wired MP sensors throw off RPM and Oil. Just a suggestion.
Click to expand...

Manifold Pressure readings are fine.

Norman CYYJ said:
Here's your problem with the Tach. The output you are using is for LS tach. The output that you want to use is PIN #6 OF THE INPUT CONNECTOR (same plug as the power leads are on).
As for the oil pressure are you using the right sender? GRT sends two senders one for oil pressure and one for fuel pressure. The lower pressure sender is for the fuel and the higher one for the oil pressure. THE OIL PRESSURE SENDER IS 0-20 BAR. The 0-5 Bar is for the fuel pressure. Make these changes and all should be good.
Have a merry Christmas.
Click to expand...

Norman - I think you and Radomir are saying the same thing on the LS Tach problem. I'll check that today. And you're sure on the senders? I thought of this and actually pulled them to verify which one I had where... and I have them 180* opposite of what you suggest. IIRC the page that came with the senders says 0-10 for fuel - and nothing specific for oil. It does give VDO part numbers for both - but neither have part numbers stamped on them. This may be the issue for the oil pressure.
 
Don't be to concerned about how clean you make the sender. The little oil will dilute. No you don't need the pull up resistor. The tach input requires the square wave pulse from the LS unit in order for it to work. The only difference on the senders is the stamp as to their pressure rating.
 
Check allowable overrange

Gsuit said:
Ok. That bit of info, along with Norman's post, is going to cause me to switch the senders around.:D Thanks guys for the good gouge.

Is there any trick to cleaning the senders of fuel / oil. The fuel I would think has flashed off and dry, but what about the oil in what will now be the fuel sender?
Click to expand...
You should check to make sure you haven't overranged your 5 bar sensor to the extent that the sensing element is permanently deformed.

-mike
 
Don't worry about whether or nor the sender was damaged. You won't be able to check it. Put it into service and if it reads properly you win, if not you loose. I doubt it very much if you hurt it. How will you know if it reads right. No fuel fuel reading will be zero. With the boost pump on it should read about 5 to 7 psi. If it does all is well. Have fun.
 
Updates

Oil Pressure
Ok, looks like Norman nailed it on the Oil Pressure. I switched my senders around where the -10bar is on the Oil Pressure, and the -5bar is now on the Fuel Pressure. Oil pressure came up much slower, peaked at 83 and after the oil temp got above 75, settled at 61psi. Score!!

Now, the fuel pressure is 0!! I'm thinking I have myself a bad sender. When GRT is back from the holidays I'm going to order another -5bar.
Thoughts?

RPM
Still reading 0.
I verified I'm using the Digital Input for the tach, because I have no connections to the Output connector on the LS box. I would like to know for sure that my pin#6 in the D-sub on the Direct Crank Sensor cable is correct but I'm not sure how to do this. I don't have a schematic for the sensor board - just the D-sub connectors. I think the wires are correct at the board - but I'd like to know I have the right wire from the board into the pin#6 location.
Anyone have the board wiring diagram?

-PS: I taxied a little today - smooth like skating on a frozen pond :D I am soooo tempted to just head on out the the end of the runway.....!
 
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