Tourmgr1

Anyone hooked up a G2X RPM feed and a Raptor shift light to the same RPM source white wire found under the dash ?
Will I have enough voltage to power both ?
TIA

spazegun2213

Turn it on and find out

I dont think the tach wire feeds voltage to the G2x, I'm 90% sure that the g2x just reads the resistance coming off that wire for the tach, so you should not have a problem.

Also, the G2x has shift lights, why would you need another?

Bill Dearborn

It is not a voltage issue. The question is whether the PCM can provide enough current to feed 3 different loads (instrument panel, g2x, and shift light) when it is designed for 1. As you draw more current through the module output circuit it's voltage output will decrease and as the current increases you will also get increased voltage drop across the wire. Not sure what the other poster meant by measuring resistance as the resistance isn't varied with RPM. The output circuit has a constant impedance and the wire has a constant resistance.

Bill

Tourmgr1

Thanks Bill,
I'll wire it up this weekend and let you know if it works.

Bill Dearborn

As long as the added loads each have a high input impedance you should be OK.

Bill

Slalom4me

I was an early adopter of the G2X and I was initially unable to
obtain a reliable trigger source for the G2X's RPM input. The tach
output from the C4 L98 distributor did not work well for driving
external devices.

After consultation with RacePak and MSD, I tried one of MSD's
products known as the Dis-Tach Driver #8913. Although marketed
for non-dist engines with multiple coil packs, it serves well as a
means of pulling a signal from the L98's electronic HEI.

The MSD Dis-Tach may be of interest to Tourmgr1. (Edited)

I have not been in touch with him for a while, but Tim at RacePak
is a superb resource. He could provide further advice in answer
to the suitability of the #8913 for Tourmgr1's purpose. Tim was
always prompt to respond to threads on the G2X forum (not to
mention emails and ph calls, as well.) A new Racepak Forum was
created sometime after RacePak merged into MSD, it looks like Tim
is now active there.

If you want to research past threads, you used to be browse topics
created in the pre-MSD/RacePak merge era at G2Extreme Forums.
Availability of the legacy forum seems to be spotty now - hopefully,
the accumulated data moves over to the new forum.

The MSD tech forum is also a good point of reference.

2008-07-22: Edited to remove erroneous information.
See explanation in following post.

.

Slalom4me

I need to retract the analogy: the Dis-Tach is NOT similar to relay.

There is no separate higher capacity circuit to drive the external
devices. I mistakenly thought I recalled wiring the #8913 to a
12VDC source but upon reviewing the instructions, I see there is
no external power source for the Dis-Tach.

Dis-Tach #8913 Installation Instructions.

.

96CollectorSport

You could use a GMR pick-up they are $40 and you just clip it around the (+) pulse wire going to a coil pack.
Here are the install instructions for the 8918.
http://www.msdignition.com/pdf/8918_89181_frm27941.pdf

Just another idea.

DOCTOR J

FYI, many GM engines with magnetic pickups in the ignition control system use trigger amplifiers
like the one below. That includes the HEI and Northstar ignitions. I haven't taken apart any of the LS-x
stuff yet (there's not much to be upgraded there) but I'd expect to find a similar circuit inside:

The 'tach output' signal for an HEI ignition (going to the ECM) comes from a design similar to the LM 1815
chip (Natn'l Semi). You see the output as an open-collector switch on pin 12 of this diagram:
http://www.thirdgen.org/techboard/at...nical-1815.jpg
The complete product tech sheets are here: http://www.national.com/ds/LM/LM1815.pdf

If the wire you are looking at using has a sqiare-wave output, it probably has a similar origin.

As such, I'd be reluctant to load up that output with external equipment, unless you KNOW it's an isolated
signal. It may draw current from the PCM 5v bus. Make a mistake there and the car might go dead
and stay that way. Look in the FSM and see if it's shown as a separate output signal from the PCM controls.
If not, you CAN still use it to drive a simple buffer transistor, and run any circuits you want from there.


ALSO:
If you only need an RPM signal for logging (and maybe a shift-light) I use the LM 2917 freq-to-volt converter:
http://www.corvetteforum.net/c4/doct...917diagram.jpg (Also Nat Semi.)

A simple 12v switch driven off the tach out gives an adequate feed signal for an RPM reading. As a bonus,
if you run a second chip as a voltage-comparitor it will drive an LED shift-light. See the manufacturer's
application sheets for detail. http://www.national.com

Any of those chips used to be $2-3 in small quantities. You do need a signal-generator to calibrate the
freq-converter. An early experimental example is here: http://www.corvetteforum.net/c4/doctorj/pix/tachs.jpg

There is a section here on older GM tach signals if you want further info: http://www.megamanual.com/index.html


It's a different topic, but if you don't need 12-channels of external data-aquisition you could look at the DATAQ
line of products. They have a little 4-ch, 10-bit A/D recorder for ~$30 (with software) that records to a laptop.
For a weekend hobby driver it's just dandy. And you don't need to leave high-buck gear in the car all the time.
Old DATAQ board: http://www.corvetteforum.net/c4/doctorj/pix/dataqsc.jpg
Main site: http://www.dataq.com/

HTH