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tneker

oil pressure safety kill switch

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Working on conversion to megasquirt after OE ECU fried at Road America last fall.  Wondering what the general consensus is around utilizing an oil pressure sensor safety switch to kill fuel injectors and try to save motor.  We don't typically have oil starvation issues so while intrigued about the approach, don't want to create a problem trying to solve a problem we haven't had.

 

Thoughts? 

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57 minutes ago, tneker said:

Working on conversion to megasquirt after OE ECU fried at Road America last fall.  Wondering what the general consensus is around utilizing an oil pressure sensor safety switch to kill fuel injectors and try to save motor.  We don't typically have oil starvation issues so while intrigued about the approach, don't want to create a problem trying to solve a problem we haven't had.

 

Thoughts? 

Our hot oil pressure at idle is very low, like 15 or less, but the high RPM pressure is 60+ or so and we ran this engine over 3000 miles last year.

My concern is that you would end up shutting off your engine any time you were at idle (creeping behind a pace car, driving in the pits, etc.) and it would be a huge nuisance.

I think a bright red light tied to a pressure switch is a better way to handle this. 

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I use a Hobbs switch set at 30 psi to turn on a very bright shift light if the pressure drops below that. The light is on at idle and pit speed but off while at race pace.

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39 minutes ago, mender said:

I use a Hobbs switch set at 30 psi to turn on a very bright shift light if the pressure drops below that. The light is on at idle and pit speed but off while at race pace.

 

Same, but 20 PSI.

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The Hobbs switch has been around forever and works fine, but since you already have the MS you can be a bit more sophisticated. For one thing instead of an on off switch use a pressure sensor, the GM pressure sensors are quite cheap and integrate well with the MS. Now that you have a channel for oil pressure you can do lots of things with it. You can log it so you can look back and see if you are getting starvation in the corners. You can send it to a digital dash and eliminate a mechanical gauge. You can set up an alarm that you can send to a digital dash or turn on a warning light, and that alarm you can apply conditions so it is only active over a certain RPM or the alarm pressure varies with RPM, this would eliminate the problem of low pressure at hot idle triggering the alarm.

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The electronic dash I made for our car knows RPM, oil pressure,  and a bunch of other things.

If the RPM is above 1500 and oil pressure is below 7.5psi per 1000rpm the "oh poop" light goes on.  We get a few blinks as the oil gets low, well before serious issues.

Our "Oh poop" light is a 1W red LED aimed at the driver's face.  Previous sane LEDs have been ignored.

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1 hour ago, mhr650 said:

The Hobbs switch has been around forever and works fine, but since you already have the MS you can be a bit more sophisticated. For one thing instead of an on off switch use a pressure sensor, the GM pressure sensors are quite cheap and integrate well with the MS. Now that you have a channel for oil pressure you can do lots of things with it. You can log it so you can look back and see if you are getting starvation in the corners. You can send it to a digital dash and eliminate a mechanical gauge. You can set up an alarm that you can send to a digital dash or turn on a warning light, and that alarm you can apply conditions so it is only active over a certain RPM or the alarm pressure varies with RPM, this would eliminate the problem of low pressure at hot idle triggering the alarm.

 

This. On my beloved neon oil pressure only activated above a certain RPM. I also set the alarm above a cut out point that would kill the engine. It is important to be able to log what your real running oil pressure is before just picking an arbitrary number. We used a ms3pro ecu and an AIM dash. if you did have a good oil leak it could save an engine. 

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21 minutes ago, erich said:

The electronic dash I made for our car knows RPM, oil pressure,  and a bunch of other things.

If the RPM is above 1500 and oil pressure is below 7.5psi per 1000rpm the "oh poop" light goes on.  We get a few blinks as the oil gets low, well before serious issues.

Our "Oh poop" light is a 1W red LED aimed at the driver's face.  Previous sane LEDs have been ignored.

 

What is doing the math and compare functions?

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12 minutes ago, red0 said:

 

What is doing the math and compare functions?

I use my Race Capture to do the exact same thing. I use various degrees of logic to take data from the sensors and output to a single, very large warning light. You basically write a little piece of code to make it do what you want. I'm sure some of the other, more expensive loggers don't require you to be a computer coder, but it's not that bad.

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I have done this, you can be fancy with a sensor or just use a switch.

 

1.

Take the brightest light you can find and connect to the ALED/WLED/FIDLE signal. I believe those signals pulls low so you need
12v -> Light -> megasquirt.

 

2a

Take a oil pressure switch (5psi?) and connect to megasquirt input such as FLEX. 
Easy and cheap.

2b,
Connect an oil pressure sensor (0-100psi) to your SPAREADC channel. This either requires a pullup from VREF or some have internal ones. I would recommend the one autosportslabs sells.
Better than the switch since you can log oil pressure and also set a more exact limit. You can also factor in RPM.


3. 
Program tunerstudio 

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I would install a GM oil level sensor as a much easier method of tracking oil level. If running the PT pan (aluminum) you could cut the housing out of a gm pan and weld it into your pan at a reasonable oil level (so slosh doesn't trip it easily). Maybe wire this into the ecu if you have issues with false alarms and give it some time delay so short midcorner sloshing doesn't trip it.

 

In my experience, once you have lost oil pressure on the 2.0 2.4 engines the damage is already done. They tend to have major oil pressure loss when the rods fly out. I had a 2.0 burning a rod bearing up (hammering sound to go with it) and the engine still had decent, although a little lower oil pressure, before it got really low when the rod escaped. The other motor lost a rod all at once, accusump was still full on shutdown. 

 

All of the other ideas above are great, just trying to put it in perspective (what are you trying to prevent) given our engine's architecture. I would log oil pressure to sort out the pan baffles and accusmp needed to prevent drop outs mid corner, after that just worry about keeping oil in it.   

Edited by Black Magic

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How's that old saying go...you don't have an oil pressure problem til you have an oil pressure gauge or something like that

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23 hours ago, red0 said:

 

What is doing the math and compare functions?

It's a full custom board based on a 32 ARM cortex M4.
I've been doing mixed signal design and embedded systems programming since the late 80's so it's pretty easy for me.

The system has been in five years now.  The tech is pretty crappy, 256x64 monochrome LCD for the five displayed values (water temp, oil temp, oil pressure, battery voltage, WBO2) it can log to USB but it's pretty flaky so I never plug one in.  It also has a three axis accelerometer that could be logged.

I'm currently making a new system that's complete overkill, because why not? 

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The reason that I use a 30 psi setting is that my rpms are usually at about 3500 rpm in the slow corners, and 30 psi for 3500 rpm is about the minimum. I baffle my pan to prevent mid-corner sloshing so any drop below 30 psi lets me know that something else is wrong. No accusump, no aerated oil and no engine failures.

 

If the accusump is active, that means the oil pump is sucking air and the engine is getting aerated oil. Very few engines can tolerate aerated oil.

 

The switch and light provides real-time feedback of any oil pressure related problems, no need to check the data after it blows up. ;)

Edited by mender
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The point at which the oil pressure light comes on:

 

Oh-Shit-Moments-064.jpg

 

Immediately after:

 

accident de train gare montparnasse suite

Edited by Burningham
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20 hours ago, mender said:

The reason that I use a 30 psi setting is that my rpms are usually at about 3500 rpm in the slow corners, and 30 psi for 3500 rpm is about the minimum. I baffle my pan to prevent mid-corner sloshing so any drop below 30 psi lets me know that something else is wrong. No accusump, no aerated oil and no engine failures.

 

If the accusump is active, that means the oil pump is sucking air and the engine is getting aerated oil. Very few engines can tolerate aerated oil.

 

The switch and light provides real-time feedback of any oil pressure related problems, no need to check the data after it blows up. ;)

 

Being picky, but for those that use accusumps the device should not allow large volumes of air into the oil system when functioning properly and installed properly. Key here is that you need to plumb the accusump early into the system, and before any anti-drainback valve (if running one in the filter).  Done properly if the oil pump pressure applied is lower than the pressure in the accusump (because you sucked air), the device will push oil down into the pump and up into rest of the engine. Not sure on the dynamics of the pickup, but I would guess the accusump would fill it as well if the device had enough volume (reason to run a 3qrt). 

 

If you run one, might be worth a look to make sure you have it plumbed the right way....

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2 hours ago, Black Magic said:

 

Being picky, but for those that use accusumps the device should not allow large volumes of air into the oil system when functioning properly and installed properly. Key here is that you need to plumb the accusump early into the system, and before any anti-drainback valve (if running one in the filter).  Done properly if the oil pump pressure applied is lower than the pressure in the accusump (because you sucked air), the device will push oil down into the pump and up into rest of the engine. Not sure on the dynamics of the pickup, but I would guess the accusump would fill it as well if the device had enough volume (reason to run a 3qrt). 

 

If you run one, might be worth a look to make sure you have it plumbed the right way....

It doesn't take large amounts of air to affect the lubrication efficiency, especially when the system pressure is down.

 

By design, the accusump only works when the system is at a lower pressure, and it stays low until the accusump is fully recharged and the cycle completed. The air that is in the pickup when the oil comes back to it has to go somewhere, and we both know where that is. So even after the pickup is in oil, it still gets a shot of air. During the first part of the cycle the engine is also seeing air, not a good combo if one expects it to live. Subject the engine to this a couple hundred times a race and it might start to talk back.

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