How many Volts to trigger an injector ?

prebordao · 09-06-2013, 03:10 AM

To the motronic gurus out there:

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

prebordao · 09-06-2013, 06:09 AM

bump

E Sully · E Sully's Garage

The injectors run on @ 12V, battery voltage.

prebordao · 09-06-2013, 06:26 AM

thx

rick-l · 09-06-2013, 07:35 AM

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.

3.2 Engine Stalling - Stumped

E Sully · E Sully's Garage

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

rick-l · 09-06-2013, 08:10 AM

Quote:

Originally Posted by E Sully

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

E Sully · E Sully's Garage

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.

rick-l · 09-06-2013, 09:20 AM

Quote:

Originally Posted by E Sully

The injectors are powered with battery voltage from the DME relay.

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.

Quote:

Originally Posted by E Sully

, just do not leave them connected for an extended period.

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.

prebordao · 09-06-2013, 09:23 AM

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

rick-l · 09-06-2013, 09:27 AM

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.

prebordao · 09-06-2013, 09:31 AM

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

sundevil64 · sundevil64's Garage

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

E Sully · E Sully's Garage

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.

911pcars · 09-06-2013, 10:53 AM

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

HawgRyder · HawgRyder's Garage

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

E Sully · E Sully's Garage

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.

911pcars · 09-06-2013, 02:34 PM

Quote:

Originally Posted by E Sully

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

E Sully · E Sully's Garage

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.

911pcars · 09-06-2013, 03:23 PM

Quote:

Originally Posted by E Sully

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