Retro-Renault Archive Forum Index  
SEARCH THE ARCHIVE FORUMS  •  Log in
Hello, you are currently browsing to Retro-Renault Archive which is a copy of our old forum. You cannot post replies in this forum. Please click here to go to the active website. 
 tachometer question
Author Message
JohnelP
Newbie

Joined: 17 Nov 2004
Posts: 13

Posted: Wed Jan 19, 2005 9:48 pm

Hello

I was browsing the net and I found some specs for tachometers.

I thought the tachometer reads a voltage from the computer, but it seems it takes the signal from the negative terminal of the coil.

Does the dash board tachometer receive a train of pulses from the ECU (as if it would come from the - terminal of the coil, and is converting the "train of pulses") or is a simple moving coil that is voltage controlled?
Chris H
Forum Moderator

Joined: 02 Mar 2004
Posts: 19978

Posted: Thu Jan 20, 2005 5:45 am

its pulsed from the ignition module.

Which is from the negative side of the coils L.T. circuit. Its the negative side thats switched, the positive side is a constant supply.
JohnelP
Newbie

Joined: 17 Nov 2004
Posts: 13

Posted: Thu Jan 20, 2005 7:16 am

I thought the dashboard tachometer is rather "silly". But it seems it is quite complicated. I've seen some IC for freq-to-voltage conversion, but they were quite expensive, so now I understand why a tachometer is regarded as a "optional feature" on many models from different brands, still.........
Chris H
Forum Moderator

Joined: 02 Mar 2004
Posts: 19978

Posted: Thu Jan 20, 2005 7:51 am

Its not so much complicated as expensive to add.

The electric ones are ten times better than the old mechanical ones. the Jones Chronometric is a good example, it was driven off a handy camshaft/etc and was slow to react so you knew what revs you were doing 20 seconds ago!
david3533
Site Subscriber

Joined: 02 Oct 2004
Posts: 1575

Posted: Thu Jan 20, 2005 8:03 am

the feed from the coil to the tacho in my experiance is white lead. one plug has 3 leads the other 1 the one with the 1 lead (brown) goes to the engine management, the other plug has yellow, white and black leads, yellow +ve from the ignition, white to tacho and black -ve. hope this is of use.
huwwatkins
Site Subscriber

Joined: 10 Jun 2004
Posts: 2317

Posted: Thu Jan 20, 2005 4:56 pm

Does the diesel tach work in the same way? As it takes a feed off the back of the alternator
Chris H
Forum Moderator

Joined: 02 Mar 2004
Posts: 19978

Posted: Fri Jan 21, 2005 5:30 am

yes leccy pulses but from the alternator instead. Quite funny if the pulleis the wrongs size, the tacho goes off the end etc.
Display posts from previous:      


 Jump to:   




SPIDER ARCHIVE
Powered by phpBB © 2001, 2002 phpBB Group :: FI Theme :: All times are GMT - 7 Hours