About two weeks ago, in the middle of a routine drive, I noticed the tach had suddenly dropped to 0 rpms. For the next 4-5 days, the first time I started the engine (after sitting over night), the tack would operate normally for about 3-4 minutes and then for no apparent reason, the needle would drop back to 0 rpms. Now on start up, needle jumps to 1,000 rpms for just an instant then drops back to 0 rpms. When I switch the ignition on, the needle moves off of the black peg to 0 rpms. All of the other dashboard gauges are functioning.

After checking the achieves, I pulled the Engine Control Module. Looked OK. Cleaned the contacts and ground anyhow. Also pulled the dashboard instrument pack. Cleaned the contacts and checked ground. No change in the tachometer operation noted.

Using an OBD II scanner, I can monitor engine speed. From this, I have concluded that a signal measuring engine speed is being generated. Don’t know if this is indicative of a faulty tachometer or something else. Have I missed something?

Don’t know if I should replace the tachometer or not. Is there any way to check it out and determine if it’s functioning correctly?

Any comments or recommendations will be greatly appreciated.


Larry (96 XJS 4.0 Liter 6I, ragtop, 51,000 miles)

 

When mine quit the problem was the resistor in the "blob" of rubber inside the amplifier. I bypassed it using a new resistor (sorry don't remember the ohm value). Was able to fit it neatly inside the amp casing and all was well. Info regarding ohm value is in "the book".


Oh dear.... just noticed your model, sorry for misdirection.

 

I have a 96 xjs as well and the tach is for the most part dead - works intermittently - more not than anything else (the car has low miles - 35k). My mechanic has advised the best way to really solve the issue is to have the tach removed and sent off to be rebuilt and reinstalled as you cannot get a new one and these were known to have issues. I think he indicated it's about $280 to have it done if you really want a tach but for an automatic trans I'm not so sure it's a high priority item.