Hotwire EFI wiring questions.

[jenand40]

I am looking into upgrading my Flapper type EFI system to the Hotwire system. I will make up a new loom and have been looking at the circuit diagram, at the top of this section on the Forum, to remove the unnecessary wiring. I believe I can remove the following parts, as I cannot see that I need them, can anyone confirm that I am correct and that the system will still run okay?
1. Speed transducer. (What does this do?)
2. Heated front screen sense. (What does this do?)
3. Diagnostic plug.
4. Fault display. (Is it worth including this?)
5. Purge control valve.
6. Lambda sensors.
7. Air condition output relay.
8. Condenser fan control.

Is there any advantage in using any of them?

Also, I cannot see how the main control relay gets it`s switched supply. There does not seem to be any feed to it! A permanent supply is feed to ECU pin 15 and the main control relay coil, but nothing going to the normally open contact of the relay. Am I missing something? I cannot believe that the circuit diagram is wrong after all this time.

Cheers.
Andy.

[ChrisJC]

I would think that the speedo input is to raise idle speed if the vehicle is moving, and that the heated screen input is to raise idle speed to compensate for the extra load on the alternator.

Chris.

[DaveEFI]

The actual ECU doesn't take much current - it simply provides a high current ground path for the injectors, via its output devices. So the high current +12v to them is fed from the main relay, which is switched by the ECU.

This might be a bit easier to follow:-


If you'd like a PDF of it which is much better quality than this JPG, drop me a PM with email address.

[RoddyO]

Hi I'm new to the forum and would just like to thank you all for your information.
Is the manual transmission resistor important. Pin 34.
Just swapped to efi and engine starts and runs but under load stutters and stalls.
I just noticed there is no resistor in line and pin 34 not earthed.