Hey guys and gals,

(First official post here, other than the intro section!)

I'm at a sticking point with my oil pressure gauge on my V12. I've recently had the instrument cluster out and apart, following Kirby's advice on cleaning everything and I installed a redundant ground as recommended. I also replaced my oil pressure sending unit with a new one, as I was recently working in the valley of the engine on the distributor and all the other flammable bits.

After I installed the oil pressure sending unit, but before I went to work on refurbishing the cluster, the oil pressure gauge on the cluster worked correctly, but only for a day (really just one key cycle). Seeing that issue pop up again led partly to the decision to clean the cluster.

So, after cleaning the cluster, I still had no visible oil pressure indication, much to my dismay! This led to some preliminary diagnosis: I have roughly 4 volts at the spade connector on the sending unit. The sending unit does change resistance readings when the engine is running and revved/idled (Ohms, I think it may have been in KOhms, but I can't remember). I have good continuity from the connector on the instrument cluster all the way to the spade terminal, and that circuit only measures 0.4 Ohms. From what I can tell of the factory wiring diagrams, the oil pressure gauge appears to share its powers and grounds with the other gauges in the cluster, leading me to believe I may just have a dead oil pressure gauge.

My main question now is, what is the best way to test the oil pressure gauge for function, and how does one go about repairing it if there's an internal issue? I don't own a gauge tester, so I'm going to need to rig something up if I need one. I'm on a very tight budget with this car and I'd love to learn how to fix gauges like this myself. Being a Ford mechanic, I could use the skills I learn here to make money at my real job later.

TL;DR version: Oil pressure gauge itself not working; how to diagnose/fix?

 

Thread bump (sorry) because I need help!

 

Assuming the dash gauge is in question??

Its been a very long time.

Inside that vertical gauge are 2????? very fine "hair wires" that do the working thing. They break. I repaired mine way back when my eyes actually could see them, no way in hell now.

Apart from dud connections where you have been working, that is all that it could be.

Only other gremlin I strike from time to time are the 2 multi pin connectors at the bottom of each side of the cluster. The slide over pin arrangement is less than satisfactory. Green growth is also an issue, and Lemon Juice (the real stuff) is what I use to clean them, with a water rinse afterwards.

Then the Smiths sender units. We had many, many at the dealer in the day that were dead in the box, or flaky at best.

I am also unsure of the 4v you are seeing, I would expect to see 12V, and I dont have an XJS here at the moment to go look at. Sold it long ago.

 

I did notice that the copper wires to all of the gauges were very, very thin when I took the cluster apart. More out of curiosity than concern, as mine seemed to be connected, but I'll double check today and update. They're really more like threads than wires, haha.

Once I get the cluster out I'll double check the connections and screws and contacts again to make sure I didn't screw anything up.

I did just replace the oil pressure sender with an aftermarket (non-Jaguar) unit less than ten miles ago, so I would assume it should be ok, although with this car, assumptions are dangerous sometimes.

Thanks for the input so far! Any idea of how I can bench test the gauge itself? I was wondering about the 4V at the sender instead of 12V, but I know that in my line of work, modern Fords use 5V of voltage as reference for inputs and some sensors like this. Wasn't sure if Jag did the same thing or not.

 

OK,

I agree with the voltage to a point.

Most cars, including Jag went to ECUY driven gauges somewhere around the late 90's, and they do indeed use 5v reference.

The V12 of the vintage we have here, only used 5v as an ECU reference for the TPS, CTS, ATS, that I can think of at the moment.

The senders are a very weak area, and as I said, we had a box of dead from new, waiting return to Smiths, and it really was hit and miss to one that worked, or even in an ohm scale that made any sense to the dash gauge.

I used a VDO unit 360006, from a Datsun, but I believe it is now NLA. It was the only one at the time that had the reverse ohms of the Smiths. Been in there 20 years and still OK working fine that I am told.