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Oil Pressure Guage


sf4018
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The last track day the oil pressure suddenly maxed out while on track.
So I got a manual oil gauge, plugged it in the engine and ran it, it was perfect. Engine is fine.

I then got a new oil pressure sensor and harness and swapped them out. Ran the engine, it maxed out again. Not a sensor issue.

I unplugged the oil pressure harness while running and the gauge froze in the position it was in (almost max).

I’m stumped what the problem could be.

Anyone have any inspiration?

 

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15 minutes ago, Pokey said:

I'll ask the obvious as I excel at that, fluid filled gauge, or was one at one point?

It's the original Caterham oil pressure gauge, dunno what type.

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I’m pretty sure it’s an electrical wiring gremlin somewhere at this point. Here’s the electrical wiring for the oil pressure sensor…E3BDC000-D0EE-4D6A-9722-CB1F3B9FDB9D.thumb.jpeg.8e27ede186705df9669226c777e0cbb4.jpeg

Not sure what the point of the 5V reference is, but the 5V, 12V and GND are testing ok. What I didn’t know until I researched the schematics is the feedback also goes to the ECU as well as the gauge (strangely via the tach), and also the unused connectors on the engine harness on the left side near the oil filter can be used to connect the oil pressure signal and a GND to something.

The signal WN52 is reading 7-8V, which is not possible for a device that can only put out 5V, so there has to be a bad ground or something like that somewhere.

Grrr.

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Not sure if it’s still true, but at one point the Caterham electrical OP gauges were known for failing or reading incorrectly.  Mine did, and I took the advice at the time and replaced it with a mechanical gauge.  No issues since.

 

Steve

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The drawing above shows 4 wires (12V supply, GND, Signal, 5V Ref). The sensor itself only has 3 wires - 12V, GND, Signal). The weird circular connector that connects the engine harness to the sensor pigtail has 4 wires on top, 3 wires on the bottom. What the heck is the 5V reference wire for? It seems the signal feedback is adding 5V, so instead of 2V (2.8 Bar) on idle it's showing 7V (off the scale)...

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2 hours ago, Croc said:

How does your wiring compare to the wiring diagram put out by the factory?

 

Pages 216 and 217 have the Duratec harness for a 420.

 

 

The drawing I made is based off of that, it’s factory wiring still. I find it hard to read without drawing it up.

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Here’s the oil pressure feedback when powered by a portable battery…

 

…it’s stable and the correct voltage level.

 

Here’s the oil pressure feedback connected to the normal supply from the car…


…it’s all over the place!

 

The ground seems solid at the connector - it stayed close to 0v to chassis and 0 ohms. 
The 12V though seemed a little erratic between 12V and 14V. How solid is the 12V supposed to be?

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9 hours ago, sf4018 said:


The 12V though seemed a little erratic between 12V and 14V. How solid is the 12V supposed to be?

 

Mine moves within 12V to 13V range.  Never known it to go above that other than the time the alternator was on its way out.   

 

How/where did you hook in the separate 12V battery? 

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5 hours ago, Croc said:

 

How/where did you hook in the separate 12V battery? 


I used the spare oil pressure sensor connector cable…it has 3 wires, 12V, 0V and signal.

666C899B-73D6-40CA-A477-635862675D1B.thumb.jpeg.789dbe36fa5e56ba13fd5bc4663abd60.jpeg

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Just for closure, it turned out to be a broken 12V (GO) wire in the engine loom somewhere near or at the oil pressure connector. The broken wire worked when the engine was not running (which made troubleshooting confusing) but with the engine running the vibration caused it to open and close, creating noise for the oil pressure sensor. I suspect my crappy dressing up of wiring in that area with the long pressure sensor cable combined with 130mph winds blowing it around was probably the cause.  That area seems pretty exposed. I've ordered a new engine loom, hopefully the engine doesn't have to come out to swap it out. 

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