Do injector and ignition coil drives require isolation?

[Healey3000]

Hi,

With respect to using "dumb" ignition coils, I see that there is some concern about having the high current drivers (ignitors) within the MS3 enclosure. That prompted the thought - should all the high-current outputs be passed through optocouplers for good measure? That would include not only spark/injectors but also things like IAC, fuel pump PWM and any solenoids.

Overkill?

Thanks.

[slow_hemi6]

Opto couplers are slow. There are definite limits to their precision. A lot of drivers contain internal protection esp if they are logic controlled. There are all sorts of high speed buffers/drivers out there much faster than an opto. These however mostly provide protection to the cpu in case of fault. The issue with coil drivers even when working correctly is they are noisy to both the main ground plane and the supply. An opto/buffer won't change that. A good ecu power supply with good filtering and smart routing of ground currents is what is required.

[Healey3000]

Opto couplers are slow. There are definite limits to their precision. A lot of drivers contain internal protection esp if they are logic controlled. There are all sorts of high speed buffers/drivers out there much faster than an opto. These however mostly provide protection to the cpu in case of fault. The issue with coil drivers even when working correctly is they are noisy to both the main ground plane and the supply. An opto/buffer won't change that. A good ecu power supply with good filtering and smart routing of ground currents is what is required.

Thank you; makes a lot of sense.

[tynt]

MS3X card seems foolproof enough. I have ISL9V coil drivers inside MS3 case and connected to MS3X spark outputs. I had bad Ford 2-wire C.O.P once, engine did not just "miss a cylinder", but also surged violently because of restarts. I'm pretty sure HV was striking back into wiring loom. Worst that happened was corrupted firmware that could be reflashed easily.