Relays

totta crolla
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Relays

Postby totta crolla » Tue Jun 21, 2022 2:49 am

So, l'm having an issue with the main efi relay getting hot.
This is probably just the relay going bad but l wanted to check the relay switching 'sequence' for the efi as l'm using a different ecu to switch the relays.
Does anyone know, from the battery +12v the order in which they are switched and the switching mode, lowside, highside?
Thanks for any help and this info. if available might be useful for others.

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jondee86
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Re: Relays

Postby jondee86 » Fri Jun 24, 2022 2:29 am

It's been a while but if I remember correctly, I think it works like this...

1. Ignition switch puts 12V directly to the Coil, Igniter and Injectors (no fuse or relay).
2. Ignition switch puts 12v to the 7.5A IGN fuse and then to the coil of the Engine Main Relay
and the coil of the EFI Main Relay.
3. The Engine Main Relay feeds 12V to the alternator via the 10A Engine fuse.
4. The EFI Main Relay gets 12V direct from the battery via the 15A EFI fuse.
5 The EFI Main Relay...
(a) feeds 12V to the Idle Up Computer, and...
(b) feeds 12V to the TVIS VSV, and...
(c) feeds 12V to B and B1 on the ECU, and...
(d) feeds 12V to the contacts of the Circuit Opening Relay. Contacts power the FP when closed.
6. The Circuit Opening Relay is initially energised by 12V directly from the ignition switch (this
wire is also the source of the 12V signal to the STA input on the ECU) while cranking. Once the
engine is running the COR is maintained ON by a ground supplied by the FC ECU output.

There are a number of AE86 wiring diagrams that show slightly different variations. On my cars
there was no failsafe "EFI Main Relay No.2" out where it could be seen, and I spent quite a few
weeks trying to figure out why the engine would not start. In the end I did find a failsafe relay
hidden away (I forget exactly where) and once I wired that in the car fired right up.

In terms of sequence, essentially all the relays are activated once the engine fires. Most have
power once the key is in the ON position but the COR does not power up until the key is in the
cranking position. Hence no priming of the FP on the AE86.

When I did my own wiring I took the ignition and injectors off the keyswitch and gave them
their own relay for power. The relay was activated by a 12V signal from the keyswitch. This
is the method that I recommend for making sure you get full 12V to the important stuff rather
than rely on worn out keyswitch contacts.

Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.

totta crolla
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Re: Relays

Postby totta crolla » Fri Jun 24, 2022 3:26 am

Well Jondee.. what can l say?
Thank you so much for taking the time to make such a comprehensive reply.
l will read through it a few times and compare it to what l have done. Thanks again, TC

totta crolla
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Re: Relays

Postby totta crolla » Sun Jun 26, 2022 6:12 am

Something l have noticed is that the fuel pump runs only when the crank sensor returns a signal to the ecu. l guess this is no bad thing but is it correct?

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jondee86
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Re: Relays

Postby jondee86 » Sun Jun 26, 2022 2:48 pm

Yes it is correct with a MAP sensored engine. It is a safety measure to prevent the FP
continuing to run in the event that the vehicle is involved in an accident that stalls the
engine. AFM sensored engines have a switch in the AFM that serves the same purpose.
Image

Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.

totta crolla
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Re: Relays

Postby totta crolla » Mon Jun 27, 2022 12:33 am

Thank you JD
l remember many Years ago making a simple and cheap alarm for a barn door.
It used a reed switch, 12v battery, relay and car horn. The problem was that the alarm would switch off when the door was closed after entering.
I was working with an electrical engineer who offered a simple solution. Using two relays the alarm could be made to stay on regardless of the reed switch.
I forgot to add a hidden overide switch... the Farmer was not happy after he let himself in :D
I guess a similar thing happens with the failsafe relay?

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jondee86
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Re: Relays

Postby jondee86 » Mon Jun 27, 2022 3:00 am

Here is a pic of how the failsafe was wired... it just interrupted the 12V supply to the injectors.

Image

The coil wire ran to an ECU pin called the FS pin and (presumably) the ECU would remove the
ground from the relay if it did not get an engine running signal within a certain (short) time.
IIRC i just gave the relay a permanent connection to ground so the at relay contacts closed as
soon as the injector power supply was switched ON.

Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.