Here's a note on how I converted my 88 300TE to EFI. Should be a similar process on any K/KE-Jet CIS cars.
I kept the stock ecu intact, which is able to control the IAC valve, though I’ve had luck with my Idle staying smooth even without the IAC plugged in. I’m also still using the stock ignition (for now).
Not having the O2 sensor connected to the stock ecu will throw a check engine light, but without the stock fuel system the check engine light is pretty much useless anyway, so I unplugged mine from the cluster. You could also rewire the check engine light to be triggered by the new ecu, which is obviously a better idea.
Parts:
ECU- I’m using a Microsquirt, but there's many other options out there.
Fuel rail- TE motorsports rail with brackets. Some people do use a stock M104 rail after modifying the brackets to hold it down on an M103.
Injectors- I went to a jump yard and took a set of OEM BMW injectors from a 2011 325i. You'll want this same style with the extended tip. I also ordered a set of EV1 connectors to wire them in.
Remove the stock injectors but leave the little plastic cups in the intake manifold. The injectors seat in these. This would be a good time to replace the o-rings that seal these in the intake as well since mine were all leaking.
The Microsquirt has 2 inj banks so I’m running cyl 1 2 3 on one bank and 4 5 6 on the other which is common. Batch firing 2 squirts per engine cycle and the engine runs better than it ever has with CIS.
Fuel Pressure Regulator- Radium 3 bar.
Fuel fittings- these allowed me to connect directly to the stock fuel feed and return lines.
>Stock feed line
> M14 male to 6AN male flare
>6AN female elbow
> fuel rail
> 8AN orb to 6AN orb swivel
> FPR
> another 6AN female elbow
> another 6AN male to M14 male
> stock return line
Crank trigger wheel- TE motorsports kit with VR sensor. I didn't have to remove the crank pulley or harmonic balancer as this one mounts on top of the crank pulley, but it did interfere with the clutch fan (I’ll try to make a spacer to reattach the clutch fan one of these days). I may also try to source a hall effect sensor to replace the VR as its having sync loss and noise issues at high RPM.
TPS- BMW
I did have to add a 1/2" spacer underneath the throttle body to make room for the tps, and also 3d printed adapters for it to fit the stock TB. DM me for part files and I’ll try to help you out.
Wideband O2- Innovate LC-2 with Bosch LSU 4.9 sensor. Many other wideband controller options available. The sensor is ever so slightly too big to fit through that hole near the passenger’s seat, so I had to widen it just a tad.
MAP- GM generic 3 bar
IAT- generic
Coolant temp- stock sensor on the head closest to the firewall.
I also used this cheap little fuse/relay box to power the ecu, injectors, and wideband. I wired it in backwards from the diagram shown so that the 12v battery feeds the two yellow "out" wires. Then the relays trigger with ignition on. The four blue are fused power, and red wire is removed.
Added a generic cone filter to fit the 80mm neck of the throttle body. Be careful that the filter doesn’t interfere with the throttle linkage.
Hope this helps! I’d like to see our car healthier than ever and I hope to keep as many on the road as long as possible.