Just installed some 650cc injectors that are low independence and I am a little confused about adjusting the PWM current limit % and time threshold. I am running Ms1 v2.2 with the flyback board installed. The manual says start the PWM current limit % at 30 and lower by 1 until the cars idle changes. I got all the way down to 5% before the car idled any different and then it shut off. I was also tapping the gas after each adjustment to make sure it still reved fine. I also messed around with the time threshold and didn't really notice much of a difference.

What is everyone running as far as these settings on low independence injectors? I have mine set at 45% and 1ms right now and the car drives fine. I just dont want to damage the injectors by not having this set correctly.

Also the stock tach is acting up since the injectors went in. I didn't touch anything else on the car but for some reason the stock tach will spaz out everynow and then. At anything above 4k it just goes all the way to 6-7k and when I accelerate from 2-3k the tack goes to 1k and sits there until I let off the throttle. If I push the gas down the tach goes back to 1 until I let off again. Any suggestions?

I did some research today and found out that running low-z injectors will cause a noisy tach signal. So can I just wire in a resister pack and set MS to run high-z injectors? I also read something about a board for MS that automatically calculates the threshold and % so you dont have to but that option was a little more than I want to put into it. My only concern with running the resister pack is idle. The threshold and % factor into the idle. What are you guys thoughts on this?

As you suggested, there are two solutions: Jean Bélanger's Peak and Hold Board and inline resistors. My professional opinion is that the P&H board is the superior option; the primary benefit being that you offload PWM responsibilities to a chip that makes duty cycle determinations on the fly. Furthermore, all of the noisy injector switching now takes place on an isolated card.

The resistors, on the other hand, reliably work. The problem is that injectors open slower since you're eliminating the current peak. This behavior hurts overall resolution and makes idling larger injectors very difficult.

I run low impedance and use the 30% mark and leave it alone.....no issues for me.

I saw the peak/hold board but the inline resistors seemed like a cheaper solution. I will have to look into it some more before I make up my mind I guess. The only problem I am having is the noisy tach signal. The car runs and idles perfect, so if I could get that problem fixed I wouldn't have to change anything.

What harness are you using? If you made your own, what type of wire is used for the tach signal?

Our wiring harness are made with shielded coaxial cable, and we advise our customers to keep the Megasquirt case from touching any chassis ground. So far none of our customers have complained about noisy tach signals, nor have we experienced it first hand.

I bought a wiring harness and tapped into all of the wires at the ECU. None of the wires are shielded. Case is not touching any metal, I find it weird that I never had 1 single spike until I switched to the new injectors.

Forgot to mention that my turbo timer displays rpms and it tapped into the RPM signal right at the ECU as works fine. Even when the stock tach starts jumping around the timer works perfect. So whats different between the 2 gauges? Maybe the stock tach is more sensitive, but when give the car any gas the tach shows 1k until I let off and the timer still works. I may try changing the settings on the injectors to see if that works.

One thing that I just thought of today. I have 2 injectors running of each wire coming from MS. Both of those wires are soldered between the connections on the plug going into the unit. Would this throw off the resistence that MS is expecting since I have it set to low-z settings? Im thinking about running a resistor pack and upgrading to the high resolution version and testing that out but Im trying to get this working first since the HR version cant control low-z injectors.

So MS has 4 injector outputs and I have 4 injectors but am only using 2 wires to transmit the signal. this is how the diagram showed to hook them up but Im wondering if this is going to impact how I install the resistor pack.

Here are a few things to consider:

Lower impedance injectors can store much more energy in them than high impedance injector of a similar inductance. Why is this information important? All of that stored energy needs to go somewhere while the injector is closed, hence the need for flyback circuitry. The flyback board, and by extension the main board, has a lot to deal with... It could also be in how the flyback board was installed (i.e. ground points, etc.).

Megasquirt only has two injector channels despite what the wiring diagrams suggest. Even though there are four pins on the connector, two pins connect to one channel and the other pins connect to the second channel.

Megasquirt does not monitor current draw or load on the injector channels. It's not "expecting" to see anything on these lines.

This configuration does not impact how you connect the injectors, nor should it impact how you connect the resistor pack. For the sake of the injector, however, you'll want one resistor for each injector (in other words, one resistor per channel will not work).

My recommendation is still the Jean's Peak and Hold (P&H) injector board. At the very least, you'll want to protect the signal from the crank angle sensor: coaxial cable with grounded sheathing is ideal, but even a twisted pair cable with one for signal and one to ground works well.

Good info. Thanks

I know the peak/hold board is the best solution at the moment and maybe when funds are a little better I will invest in that solution. I think I am just going to put some resistors on an extra injector harness I have and see how the car runs then. Maybe in a few months I will get the peak/hold board depending on how the car is running.


Also warmup enrich seems to not be working at all. Car will not run with out tapping the gas until it is fully warmed up then it idles perfect. I have jacked the warmup enrich to 150% 175% 200% and it will still lean out to 17-19 at idle when around 50*. Worked perfect before switching the injectors so not sure whats going on. Going to install resistors in the next few days so maybe that will help.

Update:

I went ahead and hooked up some resistors to the injectors and set MS to high-z settings. Car runs fine, tach works again and the warmup is working. Since then I have upgraded to the HighRes code which is running awesome by the way. Anyways I have the car tuned to 16psi and the duty cycles on my 650s are at 65%. So hears the question.. When I was running them as low-z injectors with MS at 15psi the DC was at around 45%. So Im assuming that not using low-z injectors the way they were designed and just throwing power at them with the resisters its causing them to not flow at their potential? If I were to switch to the Peak/Hold board would it lower the duty cylce of these injectors and push more fuel? Upgrading to the P/H board would be cheaper than new injectors.

I wouldn't say the injectors will flow more with the P&H board, but you will definitely have better, more precise control over them. Adding resistors to low impedance solenoids decreased their reaction time. The P&H board, on the other hand, controls these injectors as they were designed to be controlled; with a PWM current limiting routine.

This negative aspect about the resistors would probably be most noticeable at idle with large injectors. Sluggish reaction times would spell a very rough idle. I don't think you necessarily have this problem now.