Megasquirt Support Forum (MSEXTRA)

I currently use high imp injectors, which are currently VERY loud, however I've found some nice fuel injectors roughly the same size, however are known to atomize the fuel better which will help with my idle tuning on my MS3x. What im wondering is what are the steps to converting my system?

Do I just put resistor packs inline to each fuel injector signal wire from the MS3x? What specific settings do I change on Tunerstudio?

It's in the manual: http://www.msextra.com/doc/ms3/fuel.html#impedance

Jean

How many injector drivers do you need? If it's just two, then PWM of the mainboard drivers will work. Otherwise, I recommend the P&H board from <jbperf.com>. Big external resistors are a (very) poor third choice; only advantage to resistors is they are cheap.

billr wrote:Big external resistors are a (very) poor third choice; only advantage to resistors is they are cheap.

Evidence?

James

Just drawing on experience with stepper-motors. Some 25-30 years ago resistors ("L/R" control) was the hot setup to improve stepper performance over just limiting the drive voltage to what the winding could take. It was better, at the expense of all the power chewed up in the resistors; which was significant in larger steppers. Then along came switch-mode controllers and we could drive 5V motors with a 60V supply. Rise time in the winding was much faster, as were usable motor rpms. That was nice, steppers could finally carry load and slew fast enough to compete with more expensive and complicated servos in many applications

That's interesting but please don't generalise to injectors unless you have personally tested it.

My experience to-date is that say 3R3 series resistors offer a simple solution for low-z injectors connected to the MS3X outputs.
I have bench tested them and a customer's car is running them.

James

I know you have done extensive injector testing. For a given injector and pressure, how does the "dead time" compare with resistor vs. mainboard PWM vs. a P&H board like Jean's? With the steppers I was driving at 20-30K (full) steps/sec, well beyond what any injector needs, so I agree "high performance" may not be needed with injectors.

jsmcortina wrote:My experience to-date is that say 3R3 series resistors offer a simple solution for low-z injectors connected to the MS3X outputs.
I have bench tested them and a customer's car is running them.

What would be an even more interesting test would be to do back-to-back comparison between the resistors and p&h drivers.

Having said that, results will vary depending on the injectors and the resistor value. From comments I've had from people using my board, some injectors simply don't work very well with resistors. That seems to be the case of gas injectors (LPG and CNG) but not only those.

Jean

billr wrote:I know you have done extensive injector testing. For a given injector and pressure, how does the "dead time" compare with resistor vs. mainboard PWM

It was something like (from memory) 0.9ms vs 0.65ms

James

jsmcortina wrote:

billr wrote:I know you have done extensive injector testing. For a given injector and pressure, how does the "dead time" compare with resistor vs. mainboard PWM

It was something like (from memory) 0.9ms vs 0.65ms

James

On the moderate sized injectors (stock TR8) I've used 3.3 ohm resistors with, it's worked well.
Note OEM series resistors can often be of larger value (I've seen 5 ohms or so), so dead time could be longer than when using the 3.3 ohm value recommended by the MSExtra docs

Jean, have you ever tested your PWM P&H against the mainboard PWM? Assuming the 2.4 ohm your boards are optimized for, as I guess the mainboard ones could be more easily customized in TS for other low-Z impedances.

One thing to be careful about is that the lowish dead time when using 3.3 Ohm resistors could come from an increased closing time (together with an increased opening time). This will have an impact on an injector non-linear region and will also mean the minimum usable pulse width will be significantly higher than the dead time. Again this will be different for each injector type.

Jean

billr wrote:Jean, have you ever tested your PWM P&H against the mainboard PWM? Assuming the 2.4 ohm your boards are optimized for, as I guess the mainboard ones could be more easily customized in TS for other low-Z impedances.

My boards are not optimised for 2.4 Ohm; they will work for any injector that require a 4A/1A peak/hold current and other values can be done by changing the sense resistor (the ratio will always be 4:1 though).

And I haven't done any test against the MS V3.0/V3.57 PWM circuit. The math for doing a specific peak/hold value through PWM is quite simple. However, that will only work at a specific battery voltage. That's one of the big advantages of my boards: the current is sensed by the circuit to always provide the same peak/hold values as long as the battery voltage can allow it. Otherwise a timer is used for the peak duration.

Jean

Yeah, I understand the sense resistor can be changed, I just figure the mainboard driver characteristics can be changed easier with software, without having to open things up. Besides the advantage you pointed out, it's kind moot if you want P&H and need more than two drivers... you either need something external, resistors or a board like yours. As you will recall, I looked into building my own (low-Z) drivers, but concluded it was far more practical to purchase from you; and I have been quite satisfied.

racingmini_mtl wrote:My boards are not optimised for 2.4 Ohm; they will work for any injector that require a 4A/1A peak/hold current and other values can be done by changing the sense resistor (the ratio will always be 4:1 though).

I misread this first time around, so for clarity (for me) I'll say -
Jean's boards work fine with 2.4R injectors.

James

jsmcortina wrote:

racingmini_mtl wrote:My boards are not optimised for 2.4 Ohm; they will work for any injector that require a 4A/1A peak/hold current and other values can be done by changing the sense resistor (the ratio will always be 4:1 though).

I misread this first time around, so for clarity (for me) I'll say -
Jean's boards work fine with 2.4R injectors.

James

I should have been clearer. The board will work with injectors from the very low impedance TBI injectors that are around 1.2 Ohm up to injectors of about 3.5 Ohm (assuming a running battery voltage of 14V).

So, 2.4 Ohm injectors will work fine but anything below 3.5 should also work. That's true as long as the 4:1 peak/hold ratio is what the injectors specs call for, which is not universal but very common.

Jean

Yeah, no doubt I misconstrued the 2.4 at "middle of the range" as being "optimized for".

I'm running a total of 4 fuel injectors with my setup. What specific drivers do I need? I'm assuming this is gona be installed inline to my fuel injector signal wire? I'm also curious, but if im running sequential injection on the MS3x, the actual board doesnt support low imp?

Where can I purchase a complete kit already assembled?

http://jbperf.com/p&h_board/index.html#Buy

Does that come assembled already?

I only sell them in kits and not assembled unit. Also, the version you linked is not ideal with with an MS3/MS3X setup because you would need to bypass the MS3X and there isn't much space to install the board inside the MS3 case.

With an MS3/MS3X setup, you're much better off with this version: http://jbperf.com/p&h_board/v2_0.html#Buy. I'm out of stock at this time but I will have a final limited batch available in about 2 weeks (there will be a small price increase of about $5). However this is still sold in kit form. There maybe someone here on the forum who could assemble one for you. Maybe Peter Florance?

Jean