tach wire general comments concerns

People measure AC voltage, not current when looking for a tach wire.  An ocilloscope would be the "best" way to see a tach wire, but a meter that reads frequency is more practical - you can buy one at Sears for $25.  Because of the ease and cheap price tag every remote start installer should have a frequency meter in their box.

I've never seen an aftermarket remote start that wouldn't work with a 5vdc square wave - the only thing that is important is that the signal goes from ground to a point higher then the switching threshold of the alarm - usually between 0.7vdc and 3vdc.  I have never seen a tach signal reach anywhere near 20,000khz and I've seen plenty of them down around 11hz.  I guess it is possible if you use a cam angle or a crank angle signal to get close to 20Khz but both sensors usually have abnormal pulse trains that make them less then ideal for pulling tach signals.

I would order the sources the complete opposite.

Best: Fuel injectors - every car has them and they all operate virtually the same way.  There is typically only one pulse per revolution but that is more then enough resolution for a remote start. Heck, I've ran two step ignition cuts solely off of fuel injector signal.  If the fuel injector signal has a high enough resolution for individual cylinder ignition cut at 6500RPM the remote start will be fine.  The other nice thing about fuel injectors is if you use a frequency meter like mentioned above every sequential fuel injector car will read the exact same reading - something like 11hz at 1000rpm and the reading will be relational throughout the entire RPM band.

Better: Ignition - again, all cars have them, but some cars utilize different switching methods (as well as different spark methods) that may create more noise on the ignition line.  The noise may lead to reliabilty issues. 

If all else fails:  RPM - It's not uncommon for RPM signals to actually be AC voltage (created by a rotating magnet).  I've seen this on GMs, Subys, and Nissans (all with my scope).  A system looking for DC pulses will struggle with a sine wave.

Are we confused now?  :)

What kind of meter is this that can be purchased at Sears??  Model number, name??? 

Thanks

Rich

Just to be clear, not all cars have an ignition system. Diesels will not have a coil.

Also, i wouldn't say the injector is the "best" place for a signal. There are some cars they simply won't work well on. Example's, Dodge Caravan and some Nissan V6. I've had some Nissan that it won't even learn on. Using the injector wire on a 3.8L in a Caravan is very irratic. IMHO the tach signal is best, coild second, and injector when all else fails.

I know i'll catch heck for this statement but personally i have the best luck with not using a tach signal at all but going voltage. Out of the thousands of RS i have done i'd say 50% are voltage. They never come back with an issue. I can however remember quite a few with tach that have. Reason for this can be...

The tach wire connection bad

The tach disconnected by a service tech(had this one many times)

The tach wire touches a hot part and melts

The tach signal is weak or incorrect

The tach wire shorted out thru the firewall hole

Being one that gets sent out in the field to correct other installers mistakes i see it all.

The Sears meter I have is a 3482139 - It's a great car meter because it's cheap and it has auto ranging.  It's not fast enough to do certain things (like measure door lock pulses) but for the price it's a great meter to have.

http://www.sears.com/shc/s/p_10153_12605_03482139000P?mv=rr

It retails for $30 but you can get it cheaper on sale - I'm almost positive I got mine 50% off during one of their big sales.

I never meant to imply that fuel injectors would be great on every vehicle - I've just had the most luck on the widest range.

I've never seen any issues with idling - that can't be a good thing!