tach, fuel injector?

you can use, tach, fuel injector, camshaft sensor, those all work.

for fuel injectors, often you want to tap into the wire that is uncommon.

howie ll wrote:

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And if you're still doing that Kia, pull the inst. panel and pick up the tach if there is one.

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oldspark wrote:

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The injector signal may have to be scaled - they may fire once, twice or multiple times per cycle - eg, once per 2 revs of sequential, once per rev if "wasted" (like a spark), or if bank fired - up to the spark rate of the engine (eg 4 or 2 times per 2 revs for a 4cyl, 6 or 3 for 6 cyl, etc).

But I'd recommend using existing tacho wires as Howie suggested, else a splug/ignition signal because many injectors are fired at fixed timing until the engine starts - eg, every 12mS (though that is only interpreted as being up to about 330RPM for an 8-cyl engine).

But injectors can change their firings per rev (RPM) whereas a spark only occurs a set number of times (multi-spark systems excluded). EG - a true sequential injector might normally fire once per 2 revs, but might increase to once per rev under high load/power to get more fuel in (if the injector does not have the required capacity).    

Things like that drive people nuts - especially those fixed in the traditional ways of engine and automotive operation.


Skip the rest unless you want extra FYI to the above.....
Old tacho's merely counted from the distributor points (spark) which fired at half the number of cylinders (ie, an 8 cylinder 4 stoke fires 8 times per 2 revs, hence 8/2 = 4 times per rev (RPM)).

But these days many are wasted spark (4 dual-coils feeding 8 cylinders) which is the same number of sparks but distributed over 4 coils (and each splug sparks twice as often as a traditional points/electronic distributor).

Then there is sequential which tends to mean one coil per splug in spark terms which translates to one injector firing per 2 engine revs.
But like spark, even single coils (like COPs - Coil On sPlug) can be fired in wasted (2x2 mode) or batch....

It is common for engines to fire splugs on both BTDCs (Before Top Dead Centres) for environmental reasons etc.
It is not uncommon for injectors to do similar. In fact some cars trigger ALL injectors at the same time (despite being in 2, 3 or 4 banks of 2 etc injectors).   

Yep - it drives many nuts!

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tedmond wrote:

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you can use, tach, fuel injector, camshaft sensor, those all work.

for fuel injectors, often you want to tap into the wire that is uncommon.

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equate wrote:

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Is there AC output on fuel injector during cranking?

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howie ll wrote:

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I'm beginning to wonder if you are capable of doing this. Asking me for a picture of inst panel removal, are you kidding? Install work 101! Most oriental cars use a printed circuit to distribute the electricity to the various gauges, warning lights etc. If it has a rev counter there will be 4 terminals at the rear, ign, ground, illumination and TACH. By the way wrapping wire round it won't do it, that's inductive follow any of these posts, remove insulation wrap your PURPLE / white wire round it, test. If it works solder and insulate. For YOUR purposes all of the above mentioned methods work and before Oldspark reams me yes it's AC from YOUR point of view. Set DMM to 20VAC, should read between 4-7 volts as you increase the revs.

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oldspark wrote:

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Crankshaft sensors are often reluctors which put out an AC signal. Just rectify it.... etc.

equate wrote:

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Is there AC output on fuel injector during cranking?

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AFAIK no injectors are AC - they are all DC.

I was saying that unlike spark, injectors may change the number of times they fire per engine cycle (ie, per 2 revs). Hence you are probably better off sensing spark.

And like spark, they might fire 1, 2, 3, 4 etc times per cycle.

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Camshaft sensors won't always work because they don't always put out stable pulse trains.  Some of them have very funky keying on them that make signals that can't easily be understood by the remote start.  I remember physically seeing the cam sensor of a VW Jetta and thinking there was no way a remote start would ever learn the signal it was gnerating!

You would be best off finding a tach wire using a frequency meter - Sears sells a Craftsman meter that reads frequency for ~$25.

When setting the meter to AC you are basically trying to read a pulsing DC signal.  The AC setting doesn't do a very good job of this and unless you've done it several times you won't have a clue what you are looking at.

howie ll wrote:

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I'm beginning to wonder if you are capable of doing this....

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I've had an issue with people referring to duty cycles as AC voltage ever since I realized that it isn't AC voltage but rather a duty cylcle (at least in most cases).

Back when I was trained at Circuit City I was told it was taught that it was AC voltage we were looking for.  Once I discovered that it wasn't AC voltage at all I then took it upon myself to "teach" my fellow installers what was really going on.  It didn't take long before I realized why they just taught people it was AC!

My big issue with it though, is that when set to AC, you can't measure anything specific.  One car may read around 1vdc and go to 2vdc near red line while another car may read 4vdc and go to 12vdc at redline.  However, if you replace the AC meter with the correct tool for the job - a frequency meter - you can then tie the measurement directly back to RPM.  For instance, most cars fuel injectors will be right around 11hz at 1Krpm and 22hz at 2krpm (and linear throughout the band).  These numbers actually represent something!

haha, now you are just being difficult!

AC = alternating current.  In the most simple form, a fuel injector can not beconsidered AC because the current does not alternate - it is either on or off.

By saying that any DC that has a duty cycle can be considered AC is saying that all DC voltages in a car can be considered AC because ALL DC voltages have a duty cycle (it may be EXTREMELY small but eventually all battery powered DC voltages will drop to 0!   :)

My two cents,

With GM's,

Avoid alternative sources for tach signal. Cam sensors, fuel injectors, etc.

We get a few jobs through my shop with SES fault codes because a r/s installer tapped onto the wrong wire.

They usually come from the stereo shops in town. The usual customer comment is, "they brought it back to the installer and they say thier install info tells them where to get the tach signal from, they are not responsible for wrong information provided, see the car dealer if you have a problem with an SES light"

Don't know why the ecm/bcm reads that there is a problem on these circuits, but it does happen.

I can't think of one GM car that has a hard to get at coil or ecm/bcm wire. 

bcae]< wrote:

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m>D.C. is a type of voltage which does NOT cross a point of reference at regular intervals.

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 I've always felt that AC means the current flow changes direction (on a regular interval).. an injector line may be pulsing its *** off, but the current direction never changes. so it's DC.

 Jim