How many Volts to trigger an injector ?
 

To the motronic gurus out there:

What's the voltage that tipically drives a fuel injector, like from a Motronic ?

bump

The injectors run on @ 12V, battery voltage.

thx

It is not that simple. See the two scope photos Ingo posted.

If you want to open them I have heard of using a 9 volt battery to limit the current or opening them very brielfly.

http://forums.pelicanparts.com/porsche-911-technical-forum/638355-3-2-engine-stalling-stumped-8.html#post6918768

They don't need to be limited to 9V. I have used 12v, and the manual states to check for battery voltage when testing.

If you just hook them up to a car battery you will let the magic smoke out very quickly.

The magic smoke makes them work right:)

The injectors are powered with battery voltage from the DME relay, which also supplies battery voltage to the DME on pins 18 and 35. They are triggered when the DME pulses the ground to each bank. They can be tested with battery voltage, just do not leave them connected for an extended period.
http://forums.pelicanparts.com/uploa...1378485157.jpg
http://forums.pelicanparts.com/uploa...1378485177.jpg
http://forums.pelicanparts.com/uploa...1378485203.jpg

His question wasn't "what voltage is supplied to the injectors" it was what does it take to operate them. I am assuming he wants to operate them to force cleaning solution through them.

Isn't that what I said? How long can you safely let the coil dissipate 130 Watts? In that scope photo you can see the DME does supply a full 12 volts, for 200 micro seconds.

Actually, I was just wondering what the typical operating voltage would be.
It's for a project I'm working on involving an injector.

There are two different types of injectors.

• The ones in your Porsche are low impedance and are driven by a peak and hold circuit.
• Some are high impedance and driven directly with the battery. These switch slower.

I'll be using for the protoype a Bosch injector from a Ford Focus. It's a 96MF-AB type.

I have also in a pinch used a 9v battery to trigger them after ultrasonically cleaning them.

Rick, calm down. I'm not trying to insult you. I did not say you were wrong that 9v won't trigger it for testing or cleaning. You are right that a steady 12v from the battery would not be good, but the original question was. "What's the voltage that tipically drives a fuel injector, like from a Motronic ?"
The Motronic injectors in the Porsche are typically driven by a pulsed 12v. I was just giving as accurate answer to the original question as I could.

I can't give you an official OEM answer, but in general (caveat follows), ECU-controlled actuators are energized by about 3V DC from the ECU.

If you want to bench test EFI injectors, try a trigger circuit using two AA batteries in series as your source voltage. IOW, begin with a lower voltage, then work your way up.

12 VDC will probably work, but the accompanying current might overheat the injector.

If your bench test also involves gasoline, take the necessary precautions.

MHO,
Sherwood

How about putting a resistor in series with the injector?
It would limit the current..but not the voltage.
And...arrange for a pulsed supply to open them.
Bob

Sherwood, I am dealing with one specific system in my posts, the Motronic used in '84-88 911's. Battery voltage does work, and is what this system was designed for. If you look at the Engine Management picture from the manual I posted it shows the power to the injectors is from the battery through the DME relay, and the manual states you should read battery voltage when testing the injector connectors. Not to mention I personally traced and tested every wire in my 1986 DME harness, and have cleaned and freed up sticky injectors with battery voltage.
I am sure some modern systems use different voltages from the ECU, but the Porsche Motronic system definitely uses battery voltage, and in typical Porsche style, non fused. If an injector smokes when testing, it already had an internal short.
If using different injection systems or injectors, then you would need to find that systems specifications.

Hi Ed,
Thanks for the clarification on DME injectors - caveats notwithstanding. Since not protected, are burned DME harnesses a very common occurrence?

Sherwood

The DME harness itself does not have many problems. Most of the problems arise from the chassis harnesses. A search of this site will turn up quite a few threads on where to add fuses to the Carrera's wiring harness to protect against common failures. While the system was protected well enough when built, with age, corrosion, brittle insulation from many years of engine heat, and neglect, quite a few have had wires heat up and melt the insulation fusing neighboring wires together. Timmy2 is building replacement harnesses for a reason.

Doesn't the DME harness contain the individual injector harness connectors? Or perhaps the "sacrificial" wires are within the chassis harness itself. I'm putting together a 3.2 transplant, so this is good info.

Thanks
S

The DME's occasionaly have to be repaired, mine was bad when I bought it, but seem to survive for the most part. I don't want to hijack, should return thread to Prebordao.

I open injectors briefly for testing using a 9v - I just tap the battery terminals and listen for the click. I have injectors get stuck after that sit when they come back from being professionally cleaned a time or two so I always test them before I put them in a motor.

Here are some data points.

Injectors use a solenoid i.e. a coil of wire around some metal that sucks the metal into the coil when current is applied to the coil.

A coil of wire (aka "inductor") has very little resistance except for the brief moment when current is first applied - after that it becomes a short circuit pretty much.

A short circuit get pretty hot.

In a peak hold injector, the current is reduced after the initial surge of current but not so much that the injector closes.

Sounds like an easy project to build a variable voltage pulse circuit with a 555 timer, a potentiometer and a few resistors and capacitors. May have to dig out the old 555 timer projects book I saw somewhere recently.

In high school (when IC's were new :eek:) we built led flashers with 555 timers, just have to remember how to do the RC time constant math again...:D

How many pulses per minute would be adequate?

the reason for the magic smoke with a car battery is because there is no current limiting circuitry. as pointed out 12 v on a 2 ohm resistance injector is a 6 amp fry job.

thats why the 9 v is way safer or even an old cube converter from some other device. i have tonnes of those in boxes from old electronic equipment.

Thanks for the tips. I'll start low.

It seems you started this thread to look into alternative injectors. I don't know how it turned into a good voltage to hold open the injectors for cleaning and such, as that is a different matter. All the 9v posts are well and good for their intended purpose, but the system is still a 12v input with a duty cycle that works at that voltage.
To get it onto the alternative injector subject again I will post some links to that topic.
http://forums.pelicanparts.com/porsche-911-technical-forum/327832-alternative-fuel-injectors.html
http://forums.pelicanparts.com/porsche-911-technical-forum/451721-buick-fuel-injectors-3-2-a.html
http://forums.pelicanparts.com/porsche-911-technical-forum/458371-another-buick-fuel-injector-story.html

Wow, great info on those threads.
In fact i'm looking at replacing the WUR with an electronic alternative. I'll keep you posted.

I'm confused now. From motronic injectors to 1974S with cis. The recommended replacement for the original wur is 0 438 140 129. I was lucky enough to find a used one cheap in the Used Parts Forum.
Check for PM.

Not sure if anyone has mentioned but it's very easy to burn up the coil inside an injector by hooking up directly to a battery source.

They are triggered in the milliseconds. Even tapping wire to a battery and releasing fast as you can is MANY times longer than they are supposed to be triggered causing overheating.

I've read tons of people burning up injectors on the Internet doing a DIY reverse flow cleaning job.

It's CIS but i'm looking to replace the wur with a home made electronic one involving an injector. My 001 is working perfectly. It's all in the interests of science.