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Low oil pressure after WOT

pogman
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MBS206 Grand Master

MBS206

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I'll check the wiring plan tomorrow.

Now when you say ALL the earth's are to the chassis, is that including the sensor ground from the ECU?

Certain items should not be grounded to the car/body/chassis, they should ground back to specific ground pins on the ECU.

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MBS206
MBS206

Modern reg stuff now, they'd have a wide input range which would push through a buck converter, it would need to be able to maintain voltage for cranking conditions (sub 9V at times). Likely runs some

Kinkstaah
Kinkstaah

Get more oil pressure sensors. I have 3 purely because trust no-one. It would be worth checking (if not already) if it happens on every shift. Like boring, 2-3 shifts at 60kph making 10kw with no

joshuaho96
joshuaho96

Easy way to verify is just use an old style mechanical gauge and go for a drive. Then you can be 100% confident if the gauge reads one thing but your sensor reads something else. Just be super careful

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pogman Collaborator

pogman

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2 minutes ago, MBS206 said:

I'll check the wiring plan tomorrow.

Now when you say ALL the earth's are to the chassis, is that including the sensor ground from the ECU?

Certain items should not be grounded to the car/body/chassis, they should ground back to specific ground pins on the ECU.

yes sorry i should of spoke better, all sensors are grounded into their specific homes in the ecu, the ecu is then grounded to the chassis itself along with the EFI relay.

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Kinkstaah Grand Master

Kinkstaah

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12 hours ago, MBS206 said:

I think definitely get a manual oil pressure gauge on it then.

Double check if it's really dropping pressure that low.

THIS.

I was losing my mind looking at the OEM gauge which does 'work' in a R34. I lost a lot of time and sanity figuring out how it works and whether I could trust it. The only downside I have now is my wiring is almost correct myself, and occasionally my working Oil pressure sensor likes to randomly spike to -11PSI once every.. oh I dunno. Hour or two? It gives an ear splitting alarm for no reason which is fun. But I know my oil pressure didn't truly drop from 45psi to -11psi to 45psi over a 0.01 second range while cruising at 60kmh in 5th gear :p

Save your sanity and know for sure!

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MBS206 Grand Master

MBS206

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Posted
2 hours ago, Kinkstaah said:

THIS.

I was losing my mind looking at the OEM gauge which does 'work' in a R34. I lost a lot of time and sanity figuring out how it works and whether I could trust it. The only downside I have now is my wiring is almost correct myself, and occasionally my working Oil pressure sensor likes to randomly spike to -11PSI once every.. oh I dunno. Hour or two? It gives an ear splitting alarm for no reason which is fun. But I know my oil pressure didn't truly drop from 45psi to -11psi to 45psi over a 0.01 second range while cruising at 60kmh in 5th gear 😛

Save your sanity and know for sure!

Oh man that sounds nasty! The fact it reads to a negative value is... Odd... That would nearly make me think is it firmware? Unless 0V doesn't equal 0psi?

Kinkstaah Grand Master

Kinkstaah

Posted
Posted

I'm honestly not sure. I wired it into the OEM ECU and my pinning the ECU and making the plug is not as perfect as the OEM would otherwise be. This is via the Torque app for ODBII. You can set an alarm, but you can't set a timed alarm. It would be nice to set the alarm threshold for being under X psi for 0.2 seconds or something like that to filter this out.

I also noticed the OEM R34 gauge has very specific intervals it sets itself to. I.e 1-2-3-4 bar, and it rounds down. So if you say have 27psi oil pressure hot, the OEM gauge will read 1 bar at idle. (GM incredibly specify 7psi per 1000 RPM so 1 bar is double what is 'needed')

This terrifying notion is what lead me to get 3 oil pressure sensors and gauges :P

  • 2 weeks later...
pogman Collaborator

pogman

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So didn't get around to installing a manual oil pressure gauge and then decided to take the car for a cruisey drive to a cars and coffee and brought the laptop along with to get another log using more gears to see if its an oil pressure issue under acceleration or after.

image.thumb.png.afd468ce11077f70612e64a2ca63de13.png

this log has 3 gears of WOT where as previous had 2 and the oil pressure dropped once on the brakes, and the same again happens here which is interesting as it shows it can hold oil pressure while under acceleration but once slowing or just the lower RPM after a pull pressure drops.

I will be chucking a manual oil pressure gauge on to confirm but so far this makes me feel it is not an electrical issue. Something else i realised is the pressure sensor also is giving temperature information and the temp stays steady the whole time which makes me feel like the sensor itself is showing a true pressure reading.

GTSBoy Grand Master

GTSBoy

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Posted
2 minutes ago, pogman said:

Something else i realised is the pressure sensor also is giving temperature information and the temp stays steady the whole time which makes me feel like the sensor itself is showing a true pressure reading.

Not in any way a logical conclusion.

Also, looking at those logs, I struggle to see how that much oil pressure can go away that fast unless you are sucking air into the pickup.

Meanwhile the ECU voltage is chucking a huge wobbly which seems to be tied to the throttle position. 100% throttle results in decreasing voltage.

It's a mess.

pogman Collaborator

pogman

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9 minutes ago, GTSBoy said:

Not in any way a logical conclusion.

Also, looking at those logs, I struggle to see how that much oil pressure can go away that fast unless you are sucking air into the pickup.

Meanwhile the ECU voltage is chucking a huge wobbly which seems to be tied to the throttle position. 100% throttle results in decreasing voltage.

It's a mess.

Ok interesting i guess ill wait till using a manual gauge before making assumptions.

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