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Adding a Check Engine Light/Debugging Poor Oil Pressure


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The background is that I believe my 96 Sunsettter was born with a carbed engine of some flavor, this has been replaced with a Monsoon 320. This was done 780 hours ago, so not recent. Because of this, there are no warning indicators on the dash. 

Anyway, when I put the boat back into the water this year, as I was pulling into the slip the oil pressure gauge dropped to zero. Obviously that stopped the opening weekend activities. The next day, armed with my meter, I found a bad connection in the cannon plug between the ECU and dash. Because I don't have any warning lights/buzzer, I'm reliant on my gauges, and those have proven to not be reliable. I'd like a little bit of redundancy for issues like oil pressure or over temp. 

From my research it looks like in the bundle to the dash, there should be a BRN/WHT wire from the ECU (MEFI 2). My question is how does this output work? Is it 12V+ when there's an issue? Or is it a switched ground? Guesses on current it can carry, I'm looking to add a light and beeper to this, probably less than 100ma. 

If anyone's interested, here's how I debugged my oil pressure indicator issue:

https://imgur.com/a/UrGmJbr

 

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I'm pretty sure mine doesn't have a lamp, and I never even thought about it not having one.  I just checked, and my OBD connector doesn't have a wire in position E.  If it had one, it should run (as Brn-Wht) to ECM J2-31 (MIL).

The manual says that the ECM grounds the wire for an MIL indication, but doesn't say how much current it will handle.  I would assume that 100 mA is a reasonable amount.  I would probably just put a buzzer in the engine compartment and not bother with a lamp on the dash.  MIL should be on in a key on, engine off situation, so it is easy to test your installation.

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Well maybe I am misremembering - boat is still in hibernation.  But I did get the warning buzzer (under the dash?) when the oil pressure dropped to zero with the old gauges.  And isn't the ECM sending out 5 volts?  I thought I saw that in the MEFI manual.

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1 hour ago, Eagleboy99 said:

Does your boat not have a Malfunction Indicator Lamp (MIL)?  My 99 does. 

Nope, unfortunately no light. 

35 minutes ago, justgary said:

I would probably just put a buzzer in the engine compartment and not bother with a lamp on the dash.  MIL should be on in a key on, engine off situation, so it is easy to test your installation.

I like this idea. Fast and easy. 

12 minutes ago, Eagleboy99 said:

And isn't the ECM sending out 5 volts? 

On what? The dash is just a direct reference between the sender and gauge. The gauge is just reading resistance between the reference and ground. I didn't investigate the switch that runs to the ECM, would make sense that's a 5v signal that's pulled to ground with the switch closed from low pressure. 

But you do/did have a buzzer under the dash? Maybe mine is just dead, I'll do some digging around this weekend and see. 

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16 minutes ago, mexicoke said:

On what? The dash is just a direct reference between the sender and gauge. The gauge is just reading resistance between the reference and ground. I didn't investigate the switch that runs to the ECM, would make sense that's a 5v signal that's pulled to ground with the switch closed from low pressure. 

But you do/did have a buzzer under the dash? Maybe mine is just dead, I'll do some digging around this weekend and see. 

I most definitely have a buzzer.  You are driving along and all of a sudden... BEEEEEEPPPPP and zero oil pressure. Scared the crap out of me.  Instant shutdown.  My wife would ask "What kind of bird is that?" LOL  Check the MEFI manuals on the Bakes or M2O sites - they have lots of diagnostic info like pull ups etc.

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6 hours ago, Eagleboy99 said:

I most definitely have a buzzer.  You are driving along and all of a sudden... BEEEEEEPPPPP and zero oil pressure. Scared the crap out of me.  Instant shutdown.  My wife would ask "What kind of bird is that?" LOL  Check the MEFI manuals on the Bakes or M2O sites - they have lots of diagnostic info like pull ups etc.

If your buzzer doesn't sound every time you turn the key on, it isn't the MIL circuit doing it.

The MIL circuit is open collector.  You can hook your buzzer's + side to 12V and the - side to the MIL circuit and it will sound when the lamp should be on.  If you want it quieter, use 5V instead.  I have a few buzzers sitting around, so I just might try this one myself!  I'm thinking I would put the buzzer directly at the ECM so I can pin it to J2-32 and 12V easily, it will be protected under the ECM cover, and that will help tone it down a bit.

I just checked this buzzer, and it seems maybe loud enough for under the hood (maybe), and draws about 20 mA at 13.8 VDC.

https://www.allelectronics.com/item/sbz-324/3-24-vdc-beeper/1.html

SBZ-204 is not nearly loud enough at 13.8 VDC.

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1 hour ago, justgary said:

If your buzzer doesn't sound every time you turn the key on, it isn't the MIL circuit doing it.

But it does.

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1 hour ago, Eagleboy99 said:

But it does.

Good to know.  Since it scared you, I assumed that you never hear the buzzer.

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10 hours ago, Eagleboy99 said:

But it does.

So your alarm goes off and the gauge on the dash drops to zero? 

That would be very concerning, it's two different sensors both showing zero oil pressure. What ended up being the issue?

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@mexicoke - From your original post, what viscosity oil are you running, GM small blocks can have very low oil pressure when warm at idle and if the gauge is not that accurate a close to zero reading may result.  You might simply get a brass T, a threaded pressure gauge and compare dash to actual.  From an engine diagnostic perspective, I do like to verify electronic gremlins with some level of mechanical comparison when possible so I am not chasing a ghost or the wrong ghost.

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1 hour ago, Woodski said:

@mexicoke - From your original post, what viscosity oil are you running, GM small blocks can have very low oil pressure when warm at idle and if the gauge is not that accurate a close to zero reading may result.  You might simply get a brass T, a threaded pressure gauge and compare dash to actual.  From an engine diagnostic perspective, I do like to verify electronic gremlins with some level of mechanical comparison when possible so I am not chasing a ghost or the wrong ghost.

I'm running 15w40. Haven't been up to full operating temp this year, last year when cold, at idle, the dash would show ~40-50psi, when hot would drop down to ~20psi. Above idle, when warm was in the 40-50 range. 

I cannot find my mechanical oil pressure gauge, it's somewhere in my garage. I like the idea of testing the accuracy of my sender/gauge combo. I likely have a tee in the kit, just got to find the damn thing. 

 

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