Intermittent Xantia Tacho

[Old-Guy]

Every once in a while over the last few months, the tachometer (rev. counter) on the Green Lady, has stopped working for a while. I've seen it suddenly die at a steady 3,000 r.p.m. on a motorway trip and then suddenly bounce back into life a few miles later. It's not a major problem, just mildly irritating.

When I was underneath last week changing the clutch cable, I noticed a white nylon sensor on the back of the engine in about the right place for counting starter ring teeth; am I right in thinking this is the tacho sender?

Are there any favourite places to look for a dirty/loose connection that fits in with this fault.

[elma]

On my cars it has always been a dirty or knackered sensor. Its cable clips in above the gearbox, could be a bad connection there. Not sure if you're looking at the right sensor or not, mine have all been black with a brown connector.

[stupidxantia]

it could be the needle lift valve on the injector closest to the timing belt ... if it's diesel of course! check the connector that plugs into for corrosion ect! Mine is temperamental at times and is getting worse but I don't want to pay £140 for the replacement injector

[Peter.N.]

The TDC sensor is on the gearbox end of the engine just below the bottom of the cylinder head, there is a connector just above it and that can develop an intermittent connection, I would give it a wiggle about and see if that affects it.

Peter

[Xantidote]

I'm assuming the sensor you're talking about is the one which faces into the flywheel, not far in (diameter wise) from where the starter ring teeth are. From memory, I think my sensor is also white, held in place by a single smallish bolt (10m A/F?).

Tacho on my '95 TD started playing up 5-6 years ago, becoming more & more temperamental as time & mileage have rolled on. Basically now it doesn't work, except very occassionally I've checked the cable's grey plug & socket fixed to the top of the gearbox, but the contacts have all looked clean, so I've given up. I think there may be something in an old thread about the sensor and it's bonded-in connecting cable being the usual culprit - don't think you're the first to raise this issue. I think the sensor is NFP.

[Peter.N.]

That sounds like the one.

Peter

[Old-Guy]

Cheers Martin and Peter!

I looked in the BoL, but couldn't find any mention of Rev Counter or Tachometer, let alone a sensor! I mentally filed the info from a post long ago that the tacho worked by counting flywheel-ring teeth with a sensor.

The 'Green Lady' is one of the very last 1.9TDs without an engine ECU, built on 23/1/1996, but to '95 MY spec. so just like yours. Died again on the way home on Tuesday. Weather permitting, I'm going to remove the air-cleaner later on today to take some photos to complete a Wiki article so I can kill two birds with one stone. I'm not going to worry too much about it, just thought that if there is a simple fix I'd do it.

Guy

[Peter.N.]

No, you are quite right it doesn't mention it but on the non electronic controlled engines they are driven from the TDC sensor, even my CXs were! On a diesel the sensor has no function except for driving the tachometer, except possibly to check the injection timing.

Peter

[stupidxantia]

So TDC sensor can cause a faulty tacho??? Mine has had a recent clutch (@100k now only 106k) so I know that that area has been disturbed very recently ... I'm going to take a look around there myself (sorry for the hijack and thnx for the info guys)

[Peter.N.]

If the sensor is not removed before the gearbox it can be damaged so that could have happened to yours although I don't think that would make it intermittent, its more than likely the connector giving trouble.

Peter