rev counter wiring

[karan]

hi guys im new to all this malarkey and i was after some help wiring up the tacho on my defi gauges. running the Vems on a 1UZFE engine with wasted spark setup. This whole setup was previously in someone elses nissan s13 and i am putting it in my PS13 silvia at present (dont think he had the tacho running though). however i am unsure where to get a tacho signal from. I dont think you can take a 12v signal from the coils as this voltage would be too high right?

I believe bob did the loom construction etc for this car so if hes about that would be great!

cheers
Karan

[rob@vems.co.uk]

Hi mate, do you have any info on the Defi guages?
What we can do is either get the stepper motor to drive the tacho, or use a 12v pull-up via a resistor through one of the spare driver channels.
Where abouts is the car?

[karan]

hi rob cheers for the quick reply!

he broke the car as i bought the engine etc off him.
its installed in mine and is only a few hrs work off running just waiting on some oil cooler pipework.
the defi gauges are the low voltage type. I realised i actually still have a dakota digital sgi-8 interface from a m5 engined e30 that i did a cpl yrs ago so ill give this a go first.

there was no integral 02 sensor on steves car, and it currently runs horrible until it warms up.
will give the dakota thingy a go i reckon save me messing about with the vems stuff at present. Shall get some pics up in project section

cheers rob!

[rob@vems.co.uk]

No problem, its easily rectified.
If the Defi's need a low voltage there is a 5v output on the VEMS that can be used in conjunction with a resistor and a spare driver pin to give the signal the gauges need.  This works fine for most of the S13s that run VEMS (Docwra's one seems to be misbehaving so I'm going to have a look at that when he gets the car back).

[karan]

Which pin is this one rob and how do I go bout wiring it many thanks again!

[rob@vems.co.uk]

Can you put a voltmeter between the tacho wire on the Defi and ground.  If theres a voltage there then its as simple as connecting the wire to a P259 channel (see below), you can test the action of grounding by quickly bouncing the exposed tacho wire off a ground source - the faster it disconnects and reconnects the higher the RPM will read.

If there is no voltage reading we'll need to connect a voltage source, via a resistor to the tacho wire, then feed it into the VEMS like so:

But in the first instance, rather than connect to the 12v supply, you'd be as well to use the 5V output from the VEMS which is on pin28 of the larger Econoseal plug, if this gives no joy then you can splice into a +12v supply easily enough.

P259
The P259 can be your choice of any of the pins marked P259

Once thats connected its a case of setting the VEMS to drive the