Is a REAL Oil Pressure Gauge Possible

[Billroot]

One of the most annoying aspects of the wonderful XK8 is the fact that the oil pressure gauge is not really a gauge at all, it's a glorified warning light made to look like a gauge. With the oil pressure switch made, the gauge travels to 12 o'clock and stays there. Anybody wondering why the "gauge" has no numbers or units now knows the reason! Why Jaguar in their wisdom thought this was a good idea defeats me. It would not have cost them more than a few quid to put in a transducer instead of a switch on the engine and do the job properly. As it is, it simply insults the owner's intelligence.

I've been wondering - would it be possible to do a conversion and have a real oil pressure gauge? At the engine end it would be necessary to retain the switch as this feeds into the ECU and I would not want to monkey with that. However it may be possible to fit a standard automotive oil pressure transducer as well using a suitable teepeice. These transducers are quite cheap - about £35.

Looking closely at the gauge itself, it appears to be a standard stepper motor driven gauge so I'm woundering if it would actually work as a gauge if given a variable voltage input. It would need a couple of wires between the transducer and the gauge but that should not be hard - It maybe possible to find some convenient unused cores in the standard loom.

So much for my idle thoughts. Has anyone out there actually done this? If not has anyone got a spare gauge they are prepared to experiment with? I've tried sourcing a second hand spare gauge without success. Of course it would be possible to replace the gauge with a VDO one but it would not look the same. Any thoughts?

[mike020150]

Style over substance has to be the reason as much as any other possibility (like cost) for this omission. I haven't checked the details but I'd guess that a zero oil pressure signal to the ECU during engine running would cause the ECU to either shut down the engine or place it in limp home mode. If so, it's easy to imagine a product development team agreeing that the purpose of the gauge was purely stylistic redolent of Jaguar's glorious past. It will be interesting to see if you can make the gauge operate properly without interfering with the ECU signals. Mike.

[Billroot]

I guess style could be the reason and I recall that models having Sat Nav don't have a "minor instrument pack".

Looking at the wiring diagrams reveals the following:
The oil pressure warning light is a separate wire and operates when the oil pressure is <3psig = <3V
The gauge has four wires:A pair for gauge movement with a 3.7-5V pulse being supplied; a pair for feedback with 5V=0psig and 3.3V=midpoint. This strongly suggests that the gauge is capable of functioning as a gauge given a suitable variable input. I also suspect that this is a standard configuration for automotive stepper motor instruments. More research needed - contributions welcome.