Citroen XM Forum

Im the same, lay the real thing out on the deck and im there, give me a wiring diagram and i could look at it for weeks and it wont help.

D

That makes me feel better!


Well I tested the brown plug and all active pins had a steady reading, however one did flutter. Pin 3A. It has a very small reading but flucuating from nothing to 0.01 I think.. Possibly the tacho sensor. I'm not sure. I traced the relevant wire to the main connecter under the LHM tank. I need to then trace it further beyond that plug, see if it goes to the sensor plug. I'm using the laid out loom and the spare engine in the garage to trace the wire routes.

Also got the glove box out, helped a tiny bit.... Most you can do is check the visible wires. They all look fine. The wires entering the car at the bulk head are nicely wrapped in tape and are held solid. Doesn't mean they are okay I suppose. I had to move the car too earlier on and the fault is very much back. No amount of ignition key wobbling stops it from occurring.

It's so frustrating, sitting in the car, the fault is there somewhere, but no idea where!! ARGH!

Keep the faith! You have solved bigger problems than this.

Rob

I would be looking for a problem similar to the one i had with my engine loom, especially since you have swapped the engine and wiggled the harness about, it seems like the signal is being contaminated with a higher voltage from the guage flicking.

D

Swap the sensor for known good or new, as already discussed.
Check all three connections between sensor and instrument.

Presuming the sensor cable is good, you could also test whether the existing sensor wiring is picking up extenal interference by shorting together all 3 sensor connections (at the sensor). This should leave the tacho needle stationary. If it still flicks about, the fault lies with the power supply to the tacho/pcb - you've already established that both of your instruments do the same thing.

That's what I'd be doing, as well as looking for stable/unstable voltages being supplied to the tachometer. A good digital voltmeter should show this.

If circuit diagrams aren't your thing, Russ, you might need a bit of help.

Few more things to check before i throw in the towel! Next is the blue dash/PCB plug to test. Also find where the black wire from the brown plug goes too. ie if it does go to the tacho sensor.

To update this saga, I think I might have found the issue, although not totally resolved, it's behaving a little better.
I traced one of the wires from the sensor plug connector to an earthing point on the engine. Used the mandarins old engine to find that, striping off the fabric wire binding. It ends up on the side of the idle stat infact.

A new earth has seen an improvement, but it's not sorted completely yet. I think my crimping is a little suspect!

Just to be sure that stat-side earthing point is a really good one, run a temporary length of cable from it to battery -ve. If it makes no difference, then the earth point was good.

Right will do. Thanks Chris.
It wasn't nessesrally the earth point itself, more the end of the wire was less than satisfactory!
All I can say is it is definitely more stable after replacing it.

Hi Russ,

I think the sensor has three connections running from it:
- signal out
- ground
- outer screening
Make sure the last two are both properly grounded.
(Accidentally grounding the first one will not do anything any harm, but should make the needle on the tacho fall to zero.)