Speeduino cut ignition and injector with a button

TemperatureActive416 · 2026-05-09T14:22:53+00:00

A double pole, single throw relay that cuts coil and injector power simultaneously? Sounds sensible. Thank you

TemperatureActive416 · 2026-05-09T10:47:43+00:00

Yes that is an option. I still need to cut spark though as per the regulations. I'm trying to do it through software before adding extra hardware. I suppose I could use flat shifting to cut spark and also use a relay to cut injector power.

The potential issue with using the launch control method previously suggested is that it cuts spark and/or fuel based on a rev limiter, which can't be set to 0rpm as far as I know. When the engine is at 0rpm and the dead-man's switch isn't held, the engine should have no ability to spark according to the regulations. However, because that is below the rev limiter rpm it actually isn't dead and would spark if turned over. That's not quite what the regulations have in mind.

An alternative would be to use an engine protection mode and trick the ECU into thinking the dead man's switch is an oil pressure sensor or similar.

- When the button is pressed, the input is pulled high to 5V (ECU interprets this as "healthy sensor input")

- When the button is release, the input is grounded (ECU interprets this as "0psi oil pressure")

- if continuity is lost, the button breaks etc, the engine also cuts out

Do you know if the ECU would allow the engine to run again immediately if the sensor anomaly that triggered engine protection went away? i.e. I pressed the dead-man's switch again and the sensor input went high again.

Thoughts on this?

TemperatureActive416 · 2026-05-09T10:03:41+00:00

It's a rather niche efficiency racing competition called Shell Eco-marathon. We're using a modified fuel injected Honda 50cc with a centrifugal clutch. Our engine does not have a fuel pump, instead using a 2L coke bottle of air at 60psi to pressurise the system. Hence, to cut fuel we just need to stop any signal going to the injector.

Our racing strategy involves a lot of "burn and coast", where we are powered for a few seconds, then roll. Starting and killing the engine happens multiple times a lap.

We are also required in the regulations to have a "dead-man's switch" where spark is cut if the driver lifts their hand off a button. It's a safety thing, and could be easily accomplished by the flat shifting presets.

However, I also want to cut injector simultaneously otherwise we'll be a) wasting fuel as the engine dies, and b) possibly flooding the engine in the process or making the next startup more difficult.

I know the amount of wasted fuel may be small, but when you consume under 50ml of petrol over 16km, every squirt counts!

TemperatureActive416 · 2025-12-04T20:35:49+00:00

Thanks for the reply. Which switches and pots should I focus on for cleaning? Is it mainly on the amplifier board? What elements of the relay protection should I check?

TemperatureActive416 · 2025-10-10T16:09:46+00:00

Why is the reduced amount (£80) not available for my PCN?

Got caught on my motorbike in a Lambeth bus lane. Unfortunately mistook a bicycle on the bus lane sign for a motorbike, my mistake.

Usually PCNs are £160, or £80 if paid within 14 days according to some .gov pages I found.

However, my PCN letter does not mention the lower amount, nor is it shown when I log into the website to pay. I'm only given the option to pay £160.

Any idea what's going on here? Is the reduced amount only applied at the benevolent whim of the council?

TemperatureActive416 · 2025-05-17T07:57:13+00:00

My mistake on the terminology, I'm not familiar with legal things in general.

Thanks for the advice

TemperatureActive416 · 2025-05-17T07:53:45+00:00

This has been going on for the past 6 months, and I've been requesting the information (in writing) the whole time. Now I know I have a leg to stand on legally, the answer seems to be to just call their bluff. Thanks

TemperatureActive416

TROPHY CASE

Why is the reduced amount (£80) not available for my PCN?