Testing VRO Alarm Without Pulling Oil Hose

[WernerF]

Maybe there a few left who still use the VRO for oil mixing.

If you do so, it's crucial that the VRO alarm is functional. So the alarm should be checked on a regular basis. This is normally done by running the engine from premix fuel, pulling the oil hose, and waiting for the alarm tone to come. But this introduces a new possible failure source and thus the engine needs to be run from premix until proper oil consumption is verified.

My suggestion is to trigger the VRO alarm electrically. This can be done with the following very simple circuit (just a few $). You don't even need a printed circuit board.





Test procedure:
1. If the engine is hard to start, start engine and warm up a little to make it start easier later. Stop engine again.
2. Turn the key switch in run position. The normal initial tone should sound.
3. Connect the alarm tester shown above to +12V (red or red/purple cable) and the tach signal (gray). After about 15s the VRO alarm should sound (very quick tone, because the inserted tach pulses are 500Hz = 5000rpm). Disconnect the alarm tester again.
4. Without turning the key switch back (as this would reset the alarm), start the engine and let it idle. Now the alarm tone should be the typical 1/2sec on and 1/2sec off tone.
5. With the next VRO pump stroke (latest after 1 minute) the alarm should stop.
Test done.

 

[boobie]

Re: Testing VRO Alarm Without Pulling Oil Hose

A mtr will idle for a long time on just straight fuel. Just don't go above 1200 rpm. Look and see what the new E-Tecs do when they run out of oil.

 

[Greg_E]

Re: Testing VRO Alarm Without Pulling Oil Hose

Nice job! No danger of running the engine without oil. It seems like a much simpler and safer way to check the VRO alarm circuit. Once you have the tester built it would be a simple and much quicker way to test.

Does this actually test that the sensor in the VRO is functioning by "tricking" the sensor which then sets the alarm, or is it just simulating an alarm condition by bypassing the sensor?

 

[WernerF]

Re: Testing VRO Alarm Without Pulling Oil Hose

Yes, it's actually the movement of the oil flow sensor that mekes the alarm stop in step 5. Without oil the alarm would continue.
The only thing tricking this test method would be that the oil flow sensor is not moved by the oil flow but somehow is moved by the pump strokes directly. I can't imagine that.

I don't know much about the E-TEC's oil system. But I'm pretty sure it's more complicated and my test method won't work with the ETECs.

 

[Greg_E]

Re: Testing VRO Alarm Without Pulling Oil Hose

You seem to have this figured out.When I get a chance I'm going to make one of these. This is so much easier and than the old way. I would think that this would be a valuable piece of test equipment for any repair techs that still work on these engines.

Thanks.

 

[Greg_E]

Re: Testing VRO Alarm Without Pulling Oil Hose

On your wiring schematic R6 is labeled 100R. Is that 100 Ohms?

If I understand you correctly, your test circuit sets the alarm, and normal operation of the oil pump and sensor clears the alarm. If there was a malfuntion of the pump or sensor or air in the line causing the sensor not to move, the alarm would not clear. Is that correct?

 

[WernerF]

Re: Testing VRO Alarm Without Pulling Oil Hose

Yes, R6 is 100 Ohms. It's just a protection in case the alarm tester is connected directly to 12V. Note that the bridge rectifier inside makes the circuit polarity-independent. I had a set of red/black cables in the drawer, but the colors are unimportant. The LED must be red because of the voltage drop. I'm pretty sure you can use a 2N3904 for the BC547 (NPN) and a 2N3906 (PNP) for the BC557 transistors.

You can test the alarm tester by connecting it to a 12V source in series with a 1kOhms resistor (as shown in the schematic). If you have an oscilloscope you can monitor the voltage across the 1k resistor. If you haven't connect a loudspeaker in series to the 1k resistor. You should be able to hear the 500Hz pulses off the speaker.

 

[WernerF]

Re: Testing VRO Alarm Without Pulling Oil Hose

If I understand you correctly, your test circuit sets the alarm, and normal operation of the oil pump and sensor clears the alarm. If there was a malfuntion of the pump or sensor or air in the line causing the sensor not to move, the alarm would not clear. Is that correct?

Yes. But if the oil pump or the oil flow sensor is the only fault in the VRO system, you don't have to test it, because you would get an alarm in any case. The problem is that meanwhile your VRO might have developed a second fault (e.g. a broken tach wire) and now isn't able to generate an alarm at all.

Step 3 makes sure that the VRO counter really counts up to 8192 and then puts on the buzzer.
Step 4 makes sure that the rectifier/regulator's tach pulses reach the VRO counter because they modulate the alarm tone.
Step 5 isn't really necessary because you would have noticed a missing counter reset during normal operation.

Here is the inside of the VRO2:

 

[Greg_E]

Re: Testing VRO Alarm Without Pulling Oil Hose

Thanks for the explanation. I think people will feel more comfortable using this knowing how it works and that the VRO is being fully tested. For example, most of us, including myself would not know that the VRO counts the tach pulses up to 8192 and then sets the alarm.
In normal operation The the oil pump would be pulsed at some number less than 8192, pushing oil past the sensor closing the reed switch which resets the counter to zero. Is that correct?

In step 3 your tester injects a simulated tach signal which runs up the counter to 8192 and sets the alarm.
With the key switch left on, the alarm remains set and the tester is removed.
The engine is then started and the tach pulses from the regulator / rectifier cause the alarm to modulate at the normal rate of 1/2 sec on/off proving the tach signal at the VRO pump is good.
After 1 minute or less the oil pump is pulsed, closing the reed valve which resets the counter to zero and the alarm goes off.

If I don't have that right, let me know, But I think I'm starting to understand this.

I do have one question. Is the oil pump powered by the pulses from the crankcase similar the fuel side of the VRO pump? I assume that is the case and would explain why the VRO doesn't receive a reset when the tester is hooked up, but does when the engine is running. I'm just guessing on that.

When I get a little time I'm going to build this. This thing is cool!

 

[WernerF]

Re: Testing VRO Alarm Without Pulling Oil Hose

In normal operation The the oil pump would be pulsed at some number less than 8192, pushing oil past the sensor closing the reed switch which resets the counter to zero. Is that correct?

Correct.

In step 3 your tester injects a simulated tach signal which runs up the counter to 8192 and sets the alarm.
With the key switch left on, the alarm remains set and the tester is removed.
The engine is then started and the tach pulses from the regulator / rectifier cause the alarm to modulate at the normal rate of 1/2 sec on/off proving the tach signal at the VRO pump is good.
After 1 minute or less the oil pump is pulsed, closing the reed valve which resets the counter to zero and the alarm goes off.

Perfectly Correct. BTW C2 in the VRO circuit makes sure that even a permanently closed reed switch does not reset the counter. The reed switch needs to execute an open-closed-transition to do so.

I do have one question. Is the oil pump powered by the pulses from the crankcase similar the fuel side of the VRO pump? I assume that is the case and would explain why the VRO doesn't receive a reset when the tester is hooked up, but does when the engine is running. I'm just guessing on that.

Yes, fuel pump and oil pump are driven by the same "air motor" which is powered by the bottom cylinder's crankcase pulses.
Here is a very good explanation about the mechanical inside.
continuousWave: Whaler: Reference: VRO Fuel-Oil Mixing

Good luck!

 

[Greg_E]

Re: Testing VRO Alarm Without Pulling Oil Hose

You can test the alarm tester by connecting it to a 12V source in series with a 1kOhms resistor (as shown in the schematic). If you have an oscilloscope you can monitor the voltage across the 1k resistor. If you haven't connect a loudspeaker in series to the 1k resistor. You should be able to hear the 500Hz pulses off the speaker.

One last question.. The 1K Ohm resistor is only needed to check the tester when hooked up to the loudspeaker. The VRO has its own internal 1kOhm resistor so it would not be needed when doing the actual VRO test. Correct?
As I'm sure you can tell, my electronics skills are limited.
I think we have covered just about everything. Anyone with some basic skills should be able to build this and also have an understanding of how and why it works. Thanks again for taking the time to design this and answer all my questions.

 

[WernerF]

Re: Testing VRO Alarm Without Pulling Oil Hose

One last question.. The 1K Ohm resistor is only needed to check the tester when hooked up to the loudspeaker. The VRO has its own internal 1kOhm resistor so it would not be needed when doing the actual VRO test. Correct?

Yes, that's correct.

 

[bperkins]

Just found this thread - going shopping soon for the parts.. Thanks for this. Great way to test everything is working properly.

 

[sumocomputers]

This makes me want to hook my VRO system back up, just so I can build this cool tool.

 

[GA_Boater]

Just found this thread - going shopping soon for the parts.. Thanks for this. Great way to test everything is working properly.

It makes me want you to start a new thread instead of waking the dead. It's two years old. Please do not post in threads with no activity for 3 or more months. Thanks.