E1, 12v, and fuel pump relays

[mattkosem]

Hi There,

My EG's fuel pump wiring is toasted, and I'm planning to add a dedicated circuit and relay to directly drive the pump on a new relay.

I see one oddity I look at the wiring diagram here: https://www.hondata.com/tech-k20-swap-wiring

E1 is a sink, and apparently provides ground to control the pump. The diagram shows it running to the 86 pin of a relay, though, which seems a little odd to me. Best practice for compatibility with diode-protected relays, as I understand it, suggests that the greater voltage potential should go to the 86 pin and 85 should go to ground.

I just wanted to confirm my understanding of the pin above is correct, and that a combination of 12v and the E1 pin connected properly with te 85/86 pins on my relay will control the pump as per the KManager setting (2 second prime, etc.). Am I understanding this correctly?

--Matt

[Hondata]

Yes, for a diode protected relay 85 and 86 should be switched.

[mattkosem]

Perfect, thank you!

[mattkosem]

Are there any known limits on the size of the relay the ECU can drive for fans, fuel, and the O2 heater? Can I safely put a pair of relays that draw 100mA in these ground triggers?

[Hondata]

Unknown. 100 mA is a lot for a relay by itself.

[mattkosem]

Unknown. 100 mA is a lot for a relay by itself.

Is it? As far as I can tell the coil current requirement for the stock EG fan relay is also ~100 mA. It seems like 100-150 mA is typical for smaller (<40a) relays and up to 250 mA is common for bigger ones. 🤷

I'm just using Picker PC785 relays. Their specs seem comparable to others with similar capabilities, though.

[Hondata]

Honda relays should be 120 ohm coil resistance. So more than 100 mA I guess but not by much.

[mattkosem]

So far so good with 2 relays. The IC controlling the relay sink looks to support up to 1A and has over-current protection, so it seems like it should be fine for the long haul.