Focus 9 OBD+ DME worth it?

[Tom]

@FTECH9

Does anyone know if the Focus 9 Sports DME is able to run low-impedance injectors (2.7ohm) without adding resistors? I haven't seen anything that suggests it can, but seems like it would have been a logical upgrade. Sent an email to Joe as well, but thought I'd ask here in case anyone here knows. I didn't follow the development/discussion on RL, so checking to see if this is something that's already come up....

[Latitude48]

From a post by Joe on Feb 18, 2025 regarding the new Mark 2 Sport DME:

"Injector Driver
Second, the injector driver is also completely redesigned. It is now a standard "peak-and-hold" driver rather than the factory "Peak-and-Modulated Hold" driver. This should solve compatibly issues with modern low inductance/resistance injectors."

[Tom]

From a post by Joe on Feb 18, 2025 regarding the new Mark 2 Sport DME:

"Injector Driver
Second, the injector driver is also completely redesigned. It is now a standard "peak-and-hold" driver rather than the factory "Peak-and-Modulated Hold" driver. This should solve compatibly issues with modern low inductance/resistance injectors."

Thank you for that! I'd still love to hear from Joe on the current draw capability without resistors. Not sure if the quirky "peak and ripple' waveform of the factory DME can cause other issues that he's referring to, or if this means his hardware can flat out deliver the current needed for a 2.7 ohm resistors without resistors? I just don't want to burn out the DME, so admittedly being extra cautious...

[Tom]

I found some of his discussion on this very topic and am comforted that he seems to say his injector driver chips can handle low impendence injectors. He also explained that the DME delivers a pre-programmed 1.25 amps to the Peak opening, and that the real question is whether that's enough/correct for the low-impedance injectors you want to use. I suppose I could run them and find out, since I don't generally see specs on peak/hold current requirements? But would love to better understand his 1.25 amp comment. Does the driver chip deliver the same 1.25 amps regardless of resistance in the injector, or try to? I'm not sure how it could with a high-z injector since the fixed battery voltage would seem to put a limit on how many amps can flow through an injector with, for example, 16 ohms of resistance... And so, I'm questioning whether I correctly understood his comment?

[NCGermerican]

I found some of his discussion on this very topic and am comforted that he seems to say his injector driver chips can handle low impendence injectors. He also explained that the DME delivers a pre-programmed 1.25 amps to the Peak opening, and that the real question is whether that's enough/correct for the low-impedance injectors you want to use. I suppose I could run them and find out, since I don't generally see specs on peak/hold current requirements? But would love to better understand his 1.25 amp comment. Does the driver chip deliver the same 1.25 amps regardless of resistance in the injector, or try to? I'm not sure how it could with a high-z injector since the fixed battery voltage would seem to put a limit on how many amps can flow through an injector with, for example, 16 ohms of resistance... And so, I'm questioning whether I correctly understood his comment?

Hey Tom -

Do you have a link for the injectors you might try out? I've been wondering the same thing. It would save a lot of time and headache if the F9 DME could handle more modern (cheaper and readily available) injectors.

It would also be great if he designed the Focus ODB software to change the FQS setting from the laptop app as opposed to manually changing it on the DME.

I'm powering my Innovate AFR gauge through the pigtail connection on my F9 DME, so I get AFR readings on the Focus ODB software - I could log a few runs to see if FQS setting 2 (-3% fuel) could help offset the insanely rich tune from the Lindsey Racing chips.

I'm also still patiently waiting to see when he releases the MAF kit. It will be between his kit and going full stand alone (MaxxECU + Kroon harness).

[Tom]

I found some of his discussion on this very topic and am comforted that he seems to say his injector driver chips can handle low impendence injectors. He also explained that the DME delivers a pre-programmed 1.25 amps to the Peak opening, and that the real question is whether that's enough/correct for the low-impedance injectors you want to use. I suppose I could run them and find out, since I don't generally see specs on peak/hold current requirements? But would love to better understand his 1.25 amp comment. Does the driver chip deliver the same 1.25 amps regardless of resistance in the injector, or try to? I'm not sure how it could with a high-z injector since the fixed battery voltage would seem to put a limit on how many amps can flow through an injector with, for example, 16 ohms of resistance... And so, I'm questioning whether I correctly understood his comment?

Hey Tom -

Do you have a link for the injectors you might try out? I've been wondering the same thing. It would save a lot of time and headache if the F9 DME could handle more modern (cheaper and readily available) injectors.

It would also be great if he designed the Focus ODB software to change the FQS setting from the laptop app as opposed to manually changing it on the DME.

I'm powering my Innovate AFR gauge through the pigtail connection on my F9 DME, so I get AFR readings on the Focus ODB software - I could log a few runs to see if FQS setting 2 (-3% fuel) could help offset the insanely rich tune from the Lindsey Racing chips.

I'm also still patiently waiting to see when he releases the MAF kit. It will be between his kit and going full stand alone (MaxxECU + Kroon harness).

Well, I'm being a lazy because I happen to have a set of the old Vitesse 55lb Siemens injectors and would love to try them. I'm going for a street friendly mostly stock set up with AFM, etc. but even with a 3.8bar FPR, I can't fuel more than 12psi with the stock injectors. I gathered from comments Joe made on RL that the drivers on his DME are capable of handling whatever current is needed, but my understanding breaks down when he talks about needing to match the driver's current output to the current requirements of the injectors. I can't find that kind of info on these NLA injectors. And I don't understand the peak and hold design (peak and ripple in the case of the factory dme) well enough to make an educated guess. If the factory DME, which supplied 1.25 amps peak current works with these injectors as long as resistors are used, and the Ftech DME can source enough current for any injector, does that mean these injectors are ok without resistors on the Ftech dme? I know @FTECH9 has lots of irons in the fire, but still hoping he sees this and sheds a bit more light. I'm guessing there are lots of old left-over 55lb siemens injectors in garages that could be put to great use if plug and play compatible with the Ftech dme....

As for programming, I've been burning my own chips in TunerPro, using an Ostrich 2.0 EPROM emulator. It's remarkably easy and opens up a world of opportunity. Changes to fuel pressure and injector flow rates is literally one cell to edit...

[BasHenneman]

I found some of his discussion on this very topic and am comforted that he seems to say his injector driver chips can handle low impendence injectors. He also explained that the DME delivers a pre-programmed 1.25 amps to the Peak opening, and that the real question is whether that's enough/correct for the low-impedance injectors you want to use. I suppose I could run them and find out, since I don't generally see specs on peak/hold current requirements? But would love to better understand his 1.25 amp comment. Does the driver chip deliver the same 1.25 amps regardless of resistance in the injector, or try to? I'm not sure how it could with a high-z injector since the fixed battery voltage would seem to put a limit on how many amps can flow through an injector with, for example, 16 ohms of resistance... And so, I'm questioning whether I correctly understood his comment?

Hey Tom -

Do you have a link for the injectors you might try out? I've been wondering the same thing. It would save a lot of time and headache if the F9 DME could handle more modern (cheaper and readily available) injectors.

It would also be great if he designed the Focus ODB software to change the FQS setting from the laptop app as opposed to manually changing it on the DME.

I'm powering my Innovate AFR gauge through the pigtail connection on my F9 DME, so I get AFR readings on the Focus ODB software - I could log a few runs to see if FQS setting 2 (-3% fuel) could help offset the insanely rich tune from the Lindsey Racing chips.

I'm also still patiently waiting to see when he releases the MAF kit. It will be between his kit and going full stand alone (MaxxECU + Kroon harness).

For the sake of modernty, best go for the MaxxECU with a harness from Kroon or me

I’ll make a post here soon with some info and updates about that! I’ll also start providing support througj Carpokes!

[FTECH9]

I found some of his discussion on this very topic and am comforted that he seems to say his injector driver chips can handle low impendence injectors. He also explained that the DME delivers a pre-programmed 1.25 amps to the Peak opening, and that the real question is whether that's enough/correct for the low-impedance injectors you want to use. I suppose I could run them and find out, since I don't generally see specs on peak/hold current requirements? But would love to better understand his 1.25 amp comment. Does the driver chip deliver the same 1.25 amps regardless of resistance in the injector, or try to? I'm not sure how it could with a high-z injector since the fixed battery voltage would seem to put a limit on how many amps can flow through an injector with, for example, 16 ohms of resistance... And so, I'm questioning whether I correctly understood his comment?

Hey Tom -

Do you have a link for the injectors you might try out? I've been wondering the same thing. It would save a lot of time and headache if the F9 DME could handle more modern (cheaper and readily available) injectors.

It would also be great if he designed the Focus ODB software to change the FQS setting from the laptop app as opposed to manually changing it on the DME.

I'm powering my Innovate AFR gauge through the pigtail connection on my F9 DME, so I get AFR readings on the Focus ODB software - I could log a few runs to see if FQS setting 2 (-3% fuel) could help offset the insanely rich tune from the Lindsey Racing chips.

I'm also still patiently waiting to see when he releases the MAF kit. It will be between his kit and going full stand alone (MaxxECU + Kroon harness).

Well, I'm being a lazy because I happen to have a set of the old Vitesse 55lb Siemens injectors and would love to try them. I'm going for a street friendly mostly stock set up with AFM, etc. but even with a 3.8bar FPR, I can't fuel more than 12psi with the stock injectors. I gathered from comments Joe made on RL that the drivers on his DME are capable of handling whatever current is needed, but my understanding breaks down when he talks about needing to match the driver's current output to the current requirements of the injectors. I can't find that kind of info on these NLA injectors. And I don't understand the peak and hold design (peak and ripple in the case of the factory dme) well enough to make an educated guess. If the factory DME, which supplied 1.25 amps peak current works with these injectors as long as resistors are used, and the Ftech DME can source enough current for any injector, does that mean these injectors are ok without resistors on the Ftech dme? I know @FTECH9 has lots of irons in the fire, but still hoping he sees this and sheds a bit more light. I'm guessing there are lots of old left-over 55lb siemens injectors in garages that could be put to great use if plug and play compatible with the Ftech dme....

As for programming, I've been burning my own chips in TunerPro, using an Ostrich 2.0 EPROM emulator. It's remarkably easy and opens up a world of opportunity. Changes to fuel pressure and injector flow rates is literally one cell to edit...

Hi Tom,

I do have “a lot of irons in the fire”, really too many and I needed to pull a few back for a while. I wish I double majored in engineering and business management. It turns out, after a certain volume of sales, my main issues are not developing technology, but strategic and operation planning.


On the subject of injector compatibility, it is understandable why there is so much confusion. This is mainly because injector manufacturers do not share technical information with any depth; that is unless you are an OE or OEM who buys a large volume and has signed an NDA. Most everything I learned has been done the hard way with countless hours in my lab analyzing the factory injector driver and reading whatever I can find on the subject.

For the Siemens 55lb injectors, compatibility with the factory DME depends on hardware and firmware:

On a hardware level, this depends on if they can function properly with the factory peak and hold current calibrations. The first key concept in low-Z injector compatibility is the injector driver ONLY cares about the current it’s supplying to the injectors. Other factors such the injector impedance (Resistance & Inductance) or the voltage supplied to them is not in any way considered. The second key concept is low-Z injector drivers have two phases “Peak” and “Hold”. The “Peak” phase starts when the DME program commands the injector “on”. This causes the injector driver to turn the transistor feeding the injectors to maximum “on” so they can charge up their inductance as fast as possible. Doing this minimizes the time it takes from the injectors being commanded on to when they actually start injecting fuel. While this is happening, the injector driver is actively measuring the current supplied to the injectors as their inductance changes up. Once the current reaches the programed “peak” current of exactly 5 Amps, it immediately switches to the “hold” phase. In the hold phase, the transistor is only partially on to restrict the current flow to the injectors. The restricted current is around ¼ of the peak current. Dropping the drive current keeps the injectors on but reduces the charge on their inductance (i.e. electromagnetic flux). This is done so when the DME commands the injectors off, the inductive charge is relatively small and thus the injectors will stop injecting fuel much faster. Generally speaking, this on/off injector delay is commonly referred to as “deadtime”.

Below is a screen capture on my oscilloscope of the DME commanding the injectors on in terms of voltage (Yellow Trace) and the injector drivers' response in terms of current output to the injectors (Blue Trace). I have annotated the Peak and Hold phases for reference.



Note that if the new aftermarket injectors require less drive current than the factory injectors, you can install a properly rated resistor in parallel to each injector to "trick" the injector driver into thinking they are drawing more current than they are. Also, even if your replacement injectors had identical flow rate and impedance (i.e. Resistance and Inductance), this does not necessarily mean they are direct-fit replacements. For example, the 944 NA and 944 Turbo injectors have very different characteristics, but the NA and Turbo DME's injector driver is calibrated identical in terms of peak and hold current.


On a firmware level, the DME program must know a couple of things about the injectors. The main parameters are flowrate and deadtime. For flowrate, you must update this in the factory DME program. I have never actually done this, but from what I understand it is a bit convoluted. Perhaps someone with experience can chime in and provide a detailed process, ideally with a TunerPro/Ostrich setup. The deadtime must also be changed in the factory DME program, but this is not critical if it is not significantly different from factory injectors. Even if it was significantly different, if your engine is operating normally, the DME will use the NOB2 sensor to “trim” the fuel mixture and compensate. However, this closed-loop compensation is slow, and it must figure it back out on every significant load transition such as idle to acceleration. Because of this, it is better to just give the DME the updated deadtime values.


Hopefully this helps!

-Joe

[Tom]

Thanks Joe -- very much appreciate you speaking up here. That all roughly lines up with what I've been reading. Your reference to 5 amps peak current is very helpful insofar as I thought your RL post implied a peak of 1.25, which had me scratching my head. (Edit on reflection: Ah-ha! The driver supplies 5 amps, splits between 4 injectors at 1.25 each?) I take from that, the DME (yours or Bosch's) will supply current until the injectors draw 5 amps (or tries to) then back off to 1.25 amps for the rest of the injection pulse, regardless of injectors. If that's correct, then to determine if my injectors are compatible, I'd need to know their peak current level and their hold current level. And if that's correct, any tips on how to determine the peak and hold currents from the actual injectors? I'm good with an o-scope and could mock up some type of adjustable current driver or whatever -- just not sure how I'd know exactly when the injectors open/close without setting up some kind of spray rig.

I've run these very injectors in the past with in-line resistors. It was my understanding that the resistors were needed to prevent the DME from over-taxing its injector drivers, but now I'm wondering how that could be if the driver monitors current draw and limits its output regardless of injector? (Edit on reflection: with less resistance in the circuit, I imagine the driver needs to work harder to limit the output to 5 amps, which results in heat -- much like a voltage regulator heats up when driven by a voltage much higher than its regulated output.)

I'd like to figure out one way or another if the old school Seimens 55lb injectors will work on your DME without resistors, so will keep at it. In the meantime, I'm tempted to get a set of High-Z 60lb Deka injectors like these, as I believe you recommended on RL...

https://fuelinjectorconnection.com/prod ... 21EALw_wcB

I do my own chips with the TunerPro/Ostrich, so have that part covered. It's not that bad actually. There are are cells for the FQS settings, so once you calculate the overall flowrate (injector and pressure) as a percentage of the stock flow rate, you literally just scale up (or down) that one cell entry. We have a thread on how to do that here somewhere.

[FTECH9]

Thanks Joe -- very much appreciate you speaking up here. That all roughly lines up with what I've been reading. Your reference to 5 amps peak current is very helpful insofar as I thought your RL post implied a peak of 1.25, which had me scratching my head. I take from that, the DME (yours or Bosch's) will supply current until the injector draws 5 amps, then back off to 1.25 amps for the rest of the injection pulse, regardless of injector. If that's correct, then to determine if my injectors are compatible, I'd need to know their peak current level and their hold current level. And if that's correct, any tips on how to determine the peak and hold currents from the actual injectors? I'm good with an o-scope and could mock up some type of adjustable current driver or whatever -- just not sure how I'd know exactly when the injectors open/close without setting up some kind of spray rig. If the injector has 2.7 ohms resistance, that roughly equates to 5amps max at 14 volts, so I imagine it's safe to conclude the peak current can't be more than 5?

I've run these very injectors in the past with in-line resistors. It was my understanding that the resistors were needed to prevent the DME from over-taxing its injector drivers, but now I'm wondering how that could be if the driver monitors current draw and limits it to 5amps and 1.25amps...?

I'd like to figure out one way or another if the old school Seimens 55lb injectors will work on your DME without resistors, so will keep at it. In the meantime, I'm tempted to get a set of High-Z 60lb Deka injectors like these, as I believe you recommended on RL...

https://fuelinjectorconnection.com/prod ... 21EALw_wcB

I do my own chips with the TunerPro/Ostrich, so have that part covered. It's not that bad actually. There are are cells for the FQS settings, so once you calculate the overall flowrate (injector and pressure) as a percentage of the stock flow rate, you literally just scale up (or down) that one cell entry. We have a thread on how to do that here somewhere.

Hi Tom,

I would love to learn how to change the factory DME program so it can support different injectors. If you could dig up the link I would very much appreciate it.


My feeling is your Siemens 55lb injectors will likely work with the factory injector driver’s default calibration of 1.25 amps per injector (5 Amp total “Peak” current). That said, it is possible to calibrate the Peak and Hold currents on our MK1 Sport DMEs (r4.0H and newer) and all OBD+ Sport DMEs. These DMEs have a single-turn POT that can adjust the Peak/Hold calibration. However, you will need a WOB2 gauge for it to work. If you have an OBD+ Sprot DME, this can be done by graphing the NOB2 Analog parameter. But if larger injectors are being installed, it is extremely advisable to invest in a good WOB2 gauge. As I am sure you agree, monitoring AFR is critical if you want to keep your engine healthy. I am writing a blog for my website that describes the Peak/Holde adjustment procedure. When it is ready I will post a link here for anyone interested.


A couple of notes from your last response:

First, the hold current for the factory DME is a little above 1.25 amps. I feel it is actually in the 1.30 to 1.35 amp range, but I have not yet done a precise measurement of it. This is mainly because the factory Bosch injector deriver uses a modulated-hold. This means I would need to integrate the pulses to get the RMS (Root Mean Squared) current ( i.e. DC equivalent current). Normally, this would not be an issue, but the factory DME has a special circuit that likely impacts this measurement. Also, the factory injector driver does not support independent Peak and Hold calibrations. The Hold current is a fixed ratio of the calibrated Peak current. Because of this, there was not much of an engineering reason to determine the exact Hold current. However, I am getting ready to start a major study of injectors and will determine this will high precision. One could read into that statement and surmise that I am actively working on fully integrated support for different fuel injectors.

Second, the effective resistance of the injectors would not be 2.7 Ohms because there are four injectors in parallel. When two identical resistances are in parallel, the resistance is cut in half. Because the 944 injectors are batch fire, the resistance the DME’s injector driver “sees” is 2.7 Ohms / 4 = 0.675 Ohms of resistance. So, using your example, the calculated current draw would be 14V / 0.675 Ohms = 21.7 Amps. Note that the injector's inductance must fully saturate (i.e. charge up) before it would flow this theoretical maximum current.

Third, I would not recommend running a resistor in series with low-Z injectors. This would limit current to the injector, but not in the way one might think. This is because any additional series resistance would only slow down how fast the injector can charge up its inductance. This would extend the Peak phase time and potentially cause a rich mixture issue at idle all the way to a possible a no-start condition if the resistance is too high.


-Joe Baumbach