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hello to everyone. I'm new, and I didn't see a post that met my specific question, so here goes. (if the question has already been asked and answered, link please)

I have a 1981 3TC that I want to make EFI because my current carb has been rebuilt (half came from a 3tc carb and lower half is from a 4AC carb), it runs great when cold but gets rough when warm, gets rougher when AC is turned on. I understand the best and easiest long term solution would be EFI, I don't want to turbo it, id like to maintain it as close to stock as I possibly can.

I know of the basics of an EFI system, such as the custom intake manifold, ECU, injectors, TPS, Throttle body, CPS (also, how do I adapt a Crank Sensor?). Other than these what do I need? Is an external fuel pump necessary, or can I use the stock one? do I need an IAC valve for the AC to work?

thanks in advance. :D
Welcome to 3TCGarage, Johnye17!

Although it has also crossed my mind before, I don't think I'd have the confidence to pull it off at my own current skill level.. But check this post out where Foxau2 threw on a 2TG EFI on his customer's 3TC. He also reportedly got 30 MPG out of it!

efi is not the easiest. A good condition stock carb or a weber or similar that can be tuned would be the easy option.

many many ways to make it efi. do you want to adapt an oem ecu or use a programmable aftermarket ecu?

yes you will need a high pressure pump. preferably a lift pump from the main tank into a surge tank with the high pressure pump sucking from the surge tank through the fuel rail and fuel regulator and back to the surge tank. the overflow from surge tank goes back to the main tank.
Or could modify the main tank to have a fuel bowl inside for the high pressure pump pickup to sit in like the factory te71 2tgeu tank and the return line from fuel rail drains back into the main tank. This system needs the pump mounted low, preferably at the fuel level in the tank. the jdm efi system has the pump attached to the diff panhard rod mount.
The efi fuel lines are larger, at least 8mm for the pressure line. You'll need high pressure hose to join the hard lines. and a high pressure fuel filter before the fuel rail.

The power to the fuel pump should ideally be powered via a relay that will shut off in the event of a crash. The factory calls this the 'circuit open relay' and it uses the afm to turn on the fuel pump relay with the engine running, but must also run when the engine is cranked. You could also use an oil pressure switch to do the same or an aftermarket ecu analogue output.

The crank trigger can be fitted direct to the crank and/or in the distributor. It will depend on which type the ECU is able to use. There are 3 main ignition systems and a few different sensor types. Those 3 are the conventional distributor with 1 spark event per crank rotation (on a 4 cyl) as found in early toyota with points or 4 lobe trigger wheel inside the distributor. There's 'wasted spark' which use only a crank sensor and finally theres sequential spark which requires BOTH crank and cam sensors.
sensors can be either VR, Hall Effect or Optical.

The std 80's toyota electronic distributor found in 3t-eu 3tgte 2tgeu and 18rgeu use a VR 'Variable Reluctance' sensor which also needs signal conditioning via an ignitor to convert it's sign wave to a square wave. they use a 4 lobe trigger wheel in the dizzy which is equivalent to 2 lobes on the crank. spark advance is still controlled with vacuum diaphram and mechanical weights like the old points dizzy. This is a basic system and those particular efi engines have a fuel-only ecu that does not control the spark. The spark happens as it passes the 4 lobes in the distributor and relies on the distributor cap and rotor to send the spark to the correct cylinder. If an aftermarket ecu is used with one of these distributors you are limited to 1 spark event per crank revolution. The accuracy of the spark is not as good as the 'wasted spark' or sequential systems that use a crank mounted trigger.

The purpose of the A/C IAC is to raise the idle when there is a load on the engine with the A/C on. If using aftermarket ecu this is not necessary as you can run an ISCV from the ecu which will maintain a set idle rpm. The a/c will work without an Idle speed control, but the engine might idle too low and cause it to stall.
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