Rev counter stopped working - VX HPC (C20XE)

[tomwyllys]

Hi all

My rev counter stopped playing ball on the recent track day at Silverstone (an excellent day by the way).  

This may seem like a silly question to some, but can anyone tell me how the tacho on C20XE engined cars is wired in (its running Jenvey's)? It is the original Caterham rev counter as far as I'm aware. 

Does it take readings from the ECU or somewhere else on the engine, I.e the cam sensor unit?  I ask this as there is a wiring connector doing nothing on the cam sensor and two female wiring connectors, also redundant, sticking out from the wiring loom coming from the dash by the steering column. I'm wondering if perhaps a connecting wire  between the two has gone AWOL?  All wiring behind the dash appears to be in order. 

See photos of cam sensor and rogue wires

​Thanks in advance

[Jonathan Kay]

If you'd like a wiring diagram please send me a Private Mail with details of the car and your email address.

Jonathan

[tomwyllys]

Thanks Jonathan. Sent PM

[Jonathan Kay]

I've sent the wiring diagram for “Vauxhall engine with carbs, pre 1993 engine” from the 1998 Assembly Guide, and the installation notes for both carburetted and injected engines. There are some comments in there about unused wires which might help with identifying yours.

If anyone has a better diagram please can I have a copy too?

Thanks

Jonathan

[Paul Deslandes]

If you're running Jenvey throttle bodies then you must also have an ECU which presumably also runs the ignition as wasted spark..

If so the tacho is usually driven from a dedicated output from the ECU.  If it's an MBE I can tell you which pin.  e.g. if it's a 956 it comes from pin 13.

The cam sensor isn't used, hence no connection.

The tacho also has a 12v and 0v (chassis) connection so check these are okay too.

You can find the entire 1995 2.0 litre Vx car build manual at

http://www.fastgrandad.co.uk/page9.html

Paul

[tomwyllys]

Paul, thanks for the infomation.  Its not running an MBE but a DTA management system.  I'll have a look into this

Tom

[Paul Deslandes]

Tom

The DTA S series use pin 2 for tacho drive.

If you send me a pm with your email address I can send you the S series manual and connector schedules if of interest

Paul

[tomwyllys]

Many thanks Paul. PM sent

[Paul Deslandes]

Reply sent

[Paul McKenzie]

Those two wires (one black, one black/white) are for the low fluid indicator on the brake master cylinder cap.  The former owner probably removed the cap as they leak on trackdays when filled to the normal line, and substituted a cap without any connections (and no leaks)