I've read the manual on this but I'd like to know other people's experiences. This engine comes stock with a dropping resistor that comes between the injectors and the 12v supply. It looks like this:
Another way is to put the resistors between the injectors and the Megasquirt. Which is better in your experience?
I know that the Megasquirt can use PWM but I've heard it doesn't work as well in this mode.
All the maker's installations I've seen have the resistors on the +12v feed. If you wanted to use that resistor pack on the ground side, you'd be restricted to one injector driver.
You could use 4 individual resistors, of course. I'm not sure if it would make any difference which side of the injector the resistor is fitted.
If you are using an MS with a V3 PCB, you can drive the injectors directly. My Rover V8 has factory low impedance injectors, and I made the decision to remove the resistors and used PWM. Since there are good reasons to do so and the rather complicated injector drivers were designed specifically for this. It's run like this for 7 years and many miles with no problems.
If you intend using sequential injection (MS3X), you will need the resistors - or add a peak and hold board. Or change the injectors to a suitable high impedance type.
jsmcortina wrote:I suggest leaving the factory resistor pack in place.
James
Interesting. I started out with B&G code, and they were fairly persuasive in the instructions that PWM was a better way. So I simply did what I was told. Be interesting to do a direct comparison. Theory says a resistor isn't going to work as well - same as with any electric motor. It reduces the peak torque over PWM - so must make the injector react more slowly to a command from the driver.
jsmcortina wrote:My logic is that it is good enough for the OEM here and the cars are designed to do tens or hundreds of thousands of miles. So why change it?
James
By that criterion I'd have stuck with the original Lucas ECU on my Rover and not gone to MS.
But I'm glad I did - it goes far better with MS that it ever did when new.
In my opinion, all three usual low impedance injector drivers have pros and cons.
The inline resistors are cheap and easy to install but they limit somewhat the usable range for both pulse width and battery voltage (fine for OEM applications).
The PWM peak&hold drivers on the MS board extend on the range and are also cheap (already included) but they have the potential of generating noise and they need tuning as well as having a fixed setup (not adapting to battery voltage or injector characteristics). They also have a very high number of components and use a large footprint (a significant part or the V3.0 and V3.57 board is used for just 2 drivers).
The linear peak&hold drivers (such as on my boards) have the disadvantage of a slightly higher cost but they drive the injectors in the most appropriate way and adapt to the voltage condition and injector impedance through current detection. They are much more compact than the MS drivers but there's a significant heat output that has to be taken into consideration.
With high impedance injectors, you simply need saturated drivers, i.e., drivers that are fully on (full battery voltage) for the duration of the pulse. That's what is on the MS3X (and Microsquirt and MS3Pro).
I should add that the current sensing P&H drivers on my board will work with high impedance injectors which is not the case with resistors and non current sensing drivers. So for a setup which could go from low to high impedance injectors, they would be useful. For a setup that will stay with high impedance injectors, they are an unneeded expense.
Thanks, everyone. I think I'll just stick to using the stock resistor for now. I've never built one of these things before and I should probably try to keep it simple.
