Technical fuel injector question

[deth2u]

I have a set of 350cc injectors 3ohm going into my mitsubishi v6, replacing my 210cc 13ohm set. My question is since these are lower impedence injectors, they will draw more current at 12.whatever volts. How will this affect operation? I was thinking about running in-line resistors to bring them back to factory specs. If they draw more current, while the car puts out enough to operate at 13 ohms, will that fry the injectors?

 

[dsmturboawd]

probably. they're not engineered to handle that many ohms.

 

[QuickerDSM]

Originally posted by deth2u
I have a set of 350cc injectors 3ohm going into my mitsubishi v6, replacing my 210cc 13ohm set. My question is since these are lower impedence injectors, they will draw more current at 12.whatever volts. How will this affect operation? I was thinking about running in-line resistors to bring them back to factory specs. If they draw more current, while the car puts out enough to operate at 13 ohms, will that fry the injectors?

Electronics are not my strong point, but they make injector driver converters for people in your situation. I think you'll pull too much load on your drivers (the ecm) and fry them. Lower ohm load = greater current pull = fried computer driver. I don't think it's as easy as just installing resistors in-line or everyone would be doing it.

Someone please correct me if I'm wrong because I'm curious about this.

Mike

 

[deth2u]

Originally posted by QuickerDSM
Electronics are not my strong point, but they make injector driver converters for people in your situation. I think you'll pull too much load on your drivers (the ecm) and fry them. Lower ohm load = greater current pull = fried computer driver. I don't think it's as easy as just installing resistors in-line or everyone would be doing it.

Someone please correct me if I'm wrong because I'm curious about this.

Mike

I called RC engineering...the tech guy didn't know.

I'm also curious. I'll go to radio shack and build a board with resistors on it, but I'm unsure how that will relate to the fuel flow.

Any of you senior members want to step up to the plate on this one? thanks

 

[QuickerDSM]

Originally posted by deth2u
I called RC engineering...the tech guy didn't know.

I'm also curious. I'll go to radio shack and build a board with resistors on it, but I'm unsure how that will relate to the fuel flow.

Any of you senior members want to step up to the plate on this one? thanks

Well I was half correct. The load induced on the injector drivers is roughly 4 times greater with a low Z (low ohm) injector so it would eventually kill your pcm/ecm, but the injectors themselves would probably fail first.

Check out the FAQ section of this link for more information on this subject. This guy also sells an injector converters. http://www.acceleronics.com/

Good luck,
Mike

 

[deth2u]

$375?!? yeah right

I think i'll engineer something.

I think i can use an amplifier on the injector signal with the alternator as a power source, diodes to protect the ecu. I have to look at the MPFI schmatic to see how this will work.

 

[Redsand187]

It is posible to wire resistors inline with the injectors to raise the over-all impedence. Many people have done it. I know a lot of the turbo 3g guy's do it, so they can run factory DSM injectors.

Without the proper impedence, your injectors will pull more current through the ECU, about 4 times as much, and you will fry the ECU. Not eventually. Most likely with in the first few minutes of operation.

 

[KenTSIII]

Just wire in an injector resistor box from something like a 3000gt or something.

 

[krustindumm]

Resistor mod is popular on 92+ Honda's to run "tiny" DSM 450's. Just wire in a resistor box from another car (85-91 FI honda's have them, usually mounted on driver's side strut tower). Can also use 10ohm resistors, but they usually don't take underhood temps/chemicals well.

Major problem is that the 3ohm injector is designed for a constant voltage, square waveform pulse. The 13ohm is a peak and hold, it gets full voltage to open, then a reduced voltage to hold open. So when you use a 3ohm with a p&h output you may have some minor problems. Usual complaints are hard hot starts and slight hesitation, but IDK how much of that is from the differences or from the tuning.

-Dustin

 

[deth2u]

Originally posted by krustindumm
Resistor mod is popular on 92+ Honda's to run "tiny" DSM 450's. Just wire in a resistor box from another car (85-91 FI honda's have them, usually mounted on driver's side strut tower). Can also use 10ohm resistors, but they usually don't take underhood temps/chemicals well.

Major problem is that the 3ohm injector is designed for a constant voltage, square waveform pulse. The 13ohm is a peak and hold, it gets full voltage to open, then a reduced voltage to hold open. So when you use a 3ohm with a p&h output you may have some minor problems. Usual complaints are hard hot starts and slight hesitation, but IDK how much of that is from the differences or from the tuning.

-Dustin

That should be easily fixed with a voltage regulator...since the results would be linear with constant voltage, the car can be tuned from there. Gonna hit radio shack tomorrow and get to work. What if the injectors were wired directly to the alternator, using the ECU only as a baseline signal, and using the alternator as an amplifier

Fuel injectors are current sensitive to standard operation, right? more current, more duty cycle, more fuel?

 

[steve]

I'm not an expert but I have done a little reading and searching.

The injector you measured at 3 ohms is considered a low impedance injector. the 12 ohm injectors are considered high impedance.

Injectors can be driven several ways. The high end drivers are peak and hold mode (people often incorrectly call a low impedance injector peak and hold) and more common drivers are saturation mode.

Peak and hold mode drivers apply full battery voltage (high current) to the injector to quickly open it and then reduce the voltage (and current) to hold the injector open.

Saturation drivers don't have the ability to reduce the reduce the voltage, they just turn the power on to open and off to close.

Both types of drivers need to be matched to the type of injector they are driving so the the correct current is used for the injector coil.

Inductors, like the coil in an injector, resist changes in voltage. So when a voltage is first applied to a coil it takes time before the full voltage is seen. The lower the impedance the faster the voltage rises. The faster the voltage rises the faster the magnetic field is generated and the injector opens.

DSM ECU's, like most ECU's, use saturation drivers designed to work well with high impedance injectors. On the turbo cars, to get better performance from the injector a low impedance injector is used with a current limiting resistor. The DC resistance of the high impedance injector and the combination of a low impedance injector plus the resistor is about the same so the current the ECU saturation driver has to sink is the same but the voltage rise time on the low impedance injector is faster.

I think Krustin got it backward. Most P&H systems use low impedance injectors to get the fastest open and close times and it's the low impedance injector that needs the reduction in voltage to avoid burning out the coil.

Back to the original question. You need to get some high wattage non-inductive 10 ohm resistors to use those low inpedance injectors on your car. Using them without the resistors can cause both the injector coil and the ECU driver to burn out. The resisters need to be at least 10 watts and non-inductive since you don't want them adding any additional delay in the injector seeing their operating voltage. Putting them in a heat sink will help them last.

The easiest solution might be to get a resister pack from a 3000GT VR4.

Steve

 

[deth2u]

Originally posted by steve
I'm not an expert but I have done a little reading and searching.

The injector you measured at 3 ohms is considered a low impedance injector. the 12 ohm injectors are considered high impedance.

Injectors can be driven several ways. The high end drivers are peak and hold mode (people often incorrectly call a low impedance injector peak and hold) and more common drivers are saturation mode.

Peak and hold mode drivers apply full battery voltage (high current) to the injector to quickly open it and then reduce the voltage (and current) to hold the injector open.

Saturation drivers don't have the ability to reduce the reduce the voltage, they just turn the power on to open and off to close.

Both types of drivers need to be matched to the type of injector they are driving so the the correct current is used for the injector coil.

Inductors, like the coil in an injector, resist changes in voltage. So when a voltage is first applied to a coil it takes time before the full voltage is seen. The lower the impedance the faster the voltage rises. The faster the voltage rises the faster the magnetic field is generated and the injector opens.

DSM ECU's, like most ECU's, use saturation drivers designed to work well with high impedance injectors. On the turbo cars, to get better performance from the injector a low impedance injector is used with a current limiting resistor. The DC resistance of the high impedance injector and the combination of a low impedance injector plus the resistor is about the same so the current the ECU saturation driver has to sink is the same but the voltage rise time on the low impedance injector is faster.

I think Krustin got it backward. Most P&H systems use low impedance injectors to get the fastest open and close times and it's the low impedance injector that needs the reduction in voltage to avoid burning out the coil.

Back to the original question. You need to get some high wattage non-inductive 10 ohm resistors to use those low inpedance injectors on your car. Using them without the resistors can cause both the injector coil and the ECU driver to burn out. The resisters need to be at least 10 watts and non-inductive since you don't want them adding any additional delay in the injector seeing their operating voltage. Putting them in a heat sink will help them last.

The easiest solution might be to get a resister pack from a 3000GT VR4.

Steve

Im actually posting from the radioshack online computer. Unfortunately, all their resistors are low wattage. Thanks for the insight steve, it's really helping. If I took the resistor box from a vr-4, would it be a direct bolt on? My other concern are the wires besides the ecu. I'm wondering if they're a high enough gauge to pull more current...

 

[nc_99_99]

The easiest solution might be to get a resister pack from a 3000GT VR4.

There, somebody said it. You eclipse guys are all running low impedance injectors with an inline resistor known as a resistor pack. Like Steve said, get a 3000gt resistor pack. If you can't find that, solder in 10 ohm high amperage resistors in the + side of the circuit.

Nathan

 

[steve]

Originally posted by deth2u
If I took the resistor box from a vr-4, would it be a direct bolt on? My other concern are the wires besides the ecu. I'm wondering if they're a high enough gauge to pull more current...

With the resistor pack in place the injector circuit doesn't draw any more current than it would with high impedance injectors.
I have no idea if the resistor pack is a direct bolt on. That depends on how the power feed is wired to the injectors. The resistor pack normally gets wired on the + side of the injector circuit, each injector to a resistor in the pack and the - side of the injectors goes to the ECU.

Steve

 

[krustindumm]

how a normal resistor box is wired

[edit=forgot label]

red = power feed, 13.5v nominal

grey box = resistor box

little white boxes in grey box = resistors

4 floating white boxes = injectors

big white box = ECM

[/edit]

 

[deth2u]

Originally posted by nc_99_99
There, somebody said it. You eclipse guys are all running low impedance injectors with an inline resistor known as a resistor pack. Like Steve said, get a 3000gt resistor pack. If you can't find that, solder in 10 ohm high amperage resistors in the + side of the circuit.

Nathan

Thanks for suggesting to fry my ecu nc_99.


steve, im curious how the resistor box functions. I don't care if it's bolt on or not, i've gotten this far already
If it increases resistance, it'll draw more power from the ECU.. aren't we back to square one? also, would i have to upgrade my wires to a lower gauge to compensate for the increased load? thanks for your help again

 

[steve]

Deth,

Voltage, current, resistance and power are interelated by what's know as Ohms Law.
E (voltage) = I (current) x R
I = E / R
R = E / I
W (power) = I^2 x R

These are the basic formulas for DC.

If you have a fixed voltage and increase the resistance, the current decreases.

Just looking at the DC side, taking a injector with a 3 ohm resistance in series with a 10 ohm resistor equals 13 ohms.
For ease of calculation lets say the electrical system puts out 13v. The current through that 12 ohm injector will be 1 Amp (13/12=1.083). The current through 10 ohm resistor and the 3 ohm injector will be 1 Amp and because of the laws of physics each element in series sees that same 1 Amp.
Ohms law tells us that the voltage across those elements will be different, the resistor will see 10v across it and 3v will be across the injector.
When no current is flowing, there is no voltage drop from the resistor and measuring the + side of the injector to ground will read 13v. When the ECU completes the circuit you would measure 3v at the + side of the injector.

If you just used the 3 ohm injector without the resistor you would have 13v/3ohms = 4.33 amps flowing and 56 watts of power consumed my that injector. (compared to 14 watts in the 12 ohm injector)

Like Krustin drew, the injector circuit has battery voltage at one end and the ECU at the other end. When the ECU wants to fire an injector it pulls (using a transistor switch) it's lead to ground causing current to flow through the resistor and injector.

Nathan was basicly correct. The 3000GT VR4 resistor pack contains 6 10 ohm high wattage resistors. On one side all 6 leads are connected to battery voltage, on the other side each resistor lead is connected to an injector. So you have one resistor per injector and one ECU driver per injector..
The DSM resistor packs have 4 resistors, one per injector.

Does this make it clearer?

Steve

 

[deth2u]

Much clearer. I thought the injectors were in parallel and each saw 12v because of that. If the MPFI system is wired in series, then voltage would be dispursed evenly. My mistake, I should've thought of that.

I'm familiar was those formulas and basic electrical theory...although i'm having a hard time finding the 6g72 MPFI wiring diagram. It isn't in the haynes manual (yet the 4g63 one is) and i haven't gotten off my ass to get a mitsubishi service manual yet.

thanks guys

 

[steve]

Do you mind telling us what car this is for?
6g72 narrows it down a bit but who knows someone might have the service manuals for your car and could provide the diagram.

Steve

 

[krustindumm]

DSM ECU's, like most ECU's, use saturation drivers designed to work well with high impedance injectors. On the turbo cars, to get better performance from the injector a low impedance injector is used with a current limiting resistor. The DC resistance of the high impedance injector and the combination of a low impedance injector plus the resistor is about the same so the current the ECU saturation driver has to sink is the same but the voltage rise time on the low impedance injector is faster.

I think Krustin got it backward. Most P&H systems use low impedance injectors to get the fastest open and close times and it's the low impedance injector that needs the reduction in voltage to avoid burning out the coil.

Are you sure I got that wrong, I haven't messed w/ it for awhile so I could be, but I was 90% sure of it. My proof, we can also derive that:

low impedance injector must disipate 1a x 3v = 3 watts
high impedance injector must disipate 1a x 13v = 13 watts

The high impedance injector must disipate more energy. Given the same aproximate external size, and that the engineers defined the correct size wire, the high impedance injector is more likely to be P&H type, to prevent burn out. The resistor box in the low impedance setup disipates the additional 10 watts.

-Dustin

 

[steve]

Originally posted by krustindumm
Are you sure I got that wrong, I haven't messed w/ it for awhile so I could be, but I was 90% sure of it.

Keep in mind I'm commenting on your statement "Major problem is that the 3ohm injector is designed for a constant voltage, square waveform pulse. The 13ohm is a peak and hold, it gets full voltage to open, then a reduced voltage to hold open. So when you use a 3ohm with a p&h output you may have some minor problems."

I think you have it backward. High impedance injectors are usually used with constant voltage, square waveform pulse (saturated) and low impedance injectors with a peak and hold waveform.

From what I can tell, P&H systems don't use current limiting resistors, the current limiting is part of the driver design.

Low impedance injectors are used to reduce the rise time of the input voltage. According to what I've read that makes the injector react faster than a high impedance injector.
The drawback is that a lower resistance coil will pass more current and you have to limit that current or risk burning out the coil. That's why low impedance injectors respond well to using a Peak and Hold driver.

My proof, we can also derive that:

low impedance injector must disipate 1a x 3v = 3 watts
high impedance injector must disipate 1a x 13v = 13 watts

During the peak, you see a higher voltage to the coil than you would running a low impedance injector saturated with a current limiting resistor. Assuming that you would use a 13v drive, for a few microseconds the low impedance injector is going to dissipate 56w. As you point out, the injector isn't going to last long at these power levels but they will quickly generate the field strength to move the solenoid and open the injector. Then the driver drops the voltage to a level needed to hold the injector open and greatly reduces the power disipation. The lower hold drive and impedance also reduces the kick when you switch them off allowing the injector to close faster.

The high impedance injector must disipate more energy. Given the same aproximate external size, and that the engineers defined the correct size wire, the high impedance injector is more likely to be P&H type, to prevent burn out. The resistor box in the low impedance setup disipates the additional 10 watts.

A high impedance injector doesn't need a P&H driver to avoid burning it out. They have enough internal resistance to run saturated. The whole idea behind P&H is to hit the injector hard at the beginning and then reduce the drive to the min needed to keep them open. You could do that with high impedance injectors but they would be slower than low impedance injectors and you need a source of greater than battery voltage to generate the peak from.

As far as I can tell, DSM ECU's don't use P&H, they run the injector saturated. They use low impedance injectors with resistors on the turbo models to get some of the performance benefits without the cost of a new ECU using a P&H driver.

I hope this makes sense, It's way past my bedtime.

Steve

 

[krustindumm]

Alright, I was mistaken. I thought that you said/meant the P&H is used with the resistor, makes more sense now.

What cars run P&H injectors with P&H circuitry, most I have seen run resistor boxes?

-Dustin

 

[deth2u]

Originally posted by steve
Do you mind telling us what car this is for?
6g72 narrows it down a bit but who knows someone might have the service manuals for your car and could provide the diagram.

Steve

It's all in my profile. I'm still looking for that diagram if anyone can help?

 

[LaserCool]

Originally posted by steve

Inductors, like the coil in an injector, resist changes in voltage. So when a voltage is first applied to a coil it takes time before the full voltage is seen. The lower the impedance the faster the voltage rises. The faster the voltage rises the faster the magnetic field is generated and the injector opens.

...

Most P&H systems use low impedance injectors to get the fastest open and close times and it's the low impedance injector that needs the reduction in voltage to avoid burning out the coil.

Sorry Steve, but you have to go a bit past Ohm's law to understand inductors. An inductor is a solenoid, a coil of wire that generates a magnetic field when current is passed through it. The change in CURRENT, not voltage, produces a change in the magnetic field.

If you're familiar with Maxwell's laws, the differential form is del x E = -dB/dt. The first term is the curl of the electric field, and that translates to the change in current through the solenoid when you do the appropriate transformations. This is a derivative of Lenz's law, and shows that current is the part responsible for magnetic fields.

Now I mention Lenz's law for two reasons, to show where the derivative Maxwellian equation comes from, and to show why the reactance (what makes up part of impedance) comes from. The total impedance of a solenoid, such as a fuel injector, is made up of two parts: the simple resistance of the wire itself, and the reactance of the coil, which is the work it takes to create a magnetic field in the coil itself. Nature opposes changes in magnetic fields, so one has to expend energy to set one up.

The reactance is a direct result of Lenz's law, which is based in the "nature opposes ghange in magneitic fields" principle. Hence, the reactance plus resistance is impedance.

Now depending on the construction of the coil, the reactance can vary with frequency of the applied current, but is usually measured in ohms at operating frequency. One thing is defnintely true however, the current, not the voltage, is responsible for the construction of a field, and that is what is resisted.

Now, you may see oscilliscope readings for impedance using a volts scale, and that's correct. Scopes cannot read current, so usually a known resistor is placed in the circuit and a voltage drop over the resistor is read. Ohm's law allows us to calculate the current indirectly from the voltage drop across a resistor.

Capacitrs resist change in voltage, by building up charge or discharging depending upon what the change in the supplied voltage is.

Now the original question was something like "can I increase the impedance by adding a resistor in series?". The simple answer is yes, and in fact you could just add in the resistor and compute the total impedance by simple addition.

 

[steve]

Originally posted by LaserCool
Sorry Steve, but you have to go a bit past Ohm's law to understand inductors. An inductor is a solenoid, a coil of wire that generates a magnetic field when current is passed through it. The change in CURRENT, not voltage, produces a change in the magnetic field.

Your correct.

I wasn't sure that going any deeper was going to get the idea across or that I'd do the concepts justice (as you have just proven). It's far too many years since I've had anyone mention Maxwell and Lenz for me to have done as good a job explaining as you just did. In my defense, I did use current in my initial draft and went back and changed it in a state of sleep deprived stupidity.

Steve