F20C -> AE86 fuel pump wiring

[70XIN]

Hi guys,

I'm wiring an F20C into my AE86. All my dash cluster and such seems to be working okay, but i have a question about the fuel pump wiring.

I am trying to retain the AE86 fuel pump relay (COR), which has a green/red FC wire that grounds the relay, which makes shit work. This is what i had my adapt running to to make the fuel pump run.

The F20C manual says that the corresponding fuel pump wire on the ECU (also called FC), is supposed to have 0V for 2 seconds when IGN switch is on, and then 12V thereafter. I tested the wire before, and it doesn't seem to ground (or produce any voltage) at all, ever. Is this because the fuel pump relay is the one giving power to that wire on the ECU? I've attached a photo of it below.

http://www.ae86drivingclub.com.au/dcimages/1/6/340459.jpg

^ This is what the S2000 fuel pump relay looks like. A15 is the fuel pump wire (FC), IG1, B1, B9 are all ignition power.

Actually my question before probably doesn't matter - literally, how do i make my car run (safely) using the standard AE86 COR? And should the fuel pump prime when you're in ignition, or only when you start the car?

**I can't "test start" my car because i have no headers, amongst other things**

I am braindead. Hope that all makes sense.

[Matt]

You'd think by powering b1 and b9 with ign along with a15 to provide the earth to green/red on the ae86 is all you need to do

If the ecu is disconnected then it wouldn't prime

[Hen may possibly be a nut]

From that diagram it looks like the FC wire (A15) should pull to ground to make the fuel pump run. I can't see how things would work if the diagram is right and it behaved as described in the manual.

Are you 100% sure A15 doesn't pull to ground (tested with a small globe or LED and resistor connected to +12V)? And is there anything that will make the ECU cut the fuel pump (missing inputs, B1, B9 disconnected, etc...)?

[haveaparty]

i have the complete loom out of an s200 for mine. if its easier to make a new loom for the fuel pump i could bring it round and copy it or something

[slide86]

ok, its been a year or two since i left the car industry so ill try to remember......but my understanding of this circuit is as:

- when you turn the ignition on voltage runs through the IG1 energizing (mr spock) that relay and grounding through terminal 3.

- this provides the BATT voltage from terminal 7 to terminal 6 - THIS TELLS THE ECU THAT THE KEY IS THE ON POSITION

- BATT voltage is also sent to the second relay via A RESISTOR, this is important because it bleeds of the voltage preventing the ST SWITCH (start signal) relay from being energized (mr spock) straight away.

Now, once you take the next step in your starting of the car, you turn the key to the START position. This is where the second circuit comes in.

- A signal is sent from the ignition switch ST SIGNAL into terminal 2, this along with the voltage through the resistor from the first circuit is enough to energize the relay and send the voltage FROM THE IG1 to the FUEL PUMP out through terminal 4.

I believe that the FC A15, terminal 1, actually has a negative signal FROM the ECU TO the relay (not the other way round). I think this happens when B1, B9 get that BATT signal from the key being in the IG1 position......

So to summarise, this relay doesnt actually provide a NEGATIVE signal for the Toyota COR to use.

The way i would go about it is, remove the POSITIVE wire on the toyota loom side that goes to the 12v of the fuel pump and insert it into the number 4 terminal of the Honda COR.......ensure that the fuel pump has a body earth and it should run.

I believe the Honda fuel pump would only prime when the engine is cranking......




Hope i have been of some help, and i hope to God you are using the factory ecu, otherwise everything i just said is for nothing......haha FML

[Matt]

So to summarise, this relay doesnt actually provide a NEGATIVE signal for the Toyota COR to use.


Happy to be proven otherwise, but looking at the diagram i can't see how it doesn't do that....

[slide86]

yeah i know what you mean, im working off the thinking that its easier to use this setup that the ecu recognizes and use the 1 wire from the Toyota loom to provide +12v to the fuel pump.....

If you added the FC wire from the toyota COR to the FC circuit in this diagram and left the Honda COR plugged in the loom also, then it might work. Im just pretty sure that this setup will need to be left as is for the circuit to operate correctly.

Having nothing connected to terminal 4 at the end of the day shouldnt make any difference to the operation of the Honda COR.

Going by what Seamus has said, it might be that the FC wire from the ECU has power and the ST SWITCH is the ground......not the other way round as i stated earlier?????

[Matt]

Reading the diagram doesn't suggest that... A15 appears to provide the earth.

I'd be checking the ecu has all inputs it needs and powers up etc

[slide86]

agreed

[70XIN]

Thanks guys :) I shall continue to look and see if i missed anything.

[Matt]

if it all becomes too hard a tachometric relay can get you by...

commonly used in lpg installations, but do it as a last resort.