Thanks for the replies.
M. I don't use picmicro ? And TBH, I don't even know what it is. It's been a long time since I messed around with electronics.
Bluejets - I have seen the 555 timers on Ebay. But, here is the issue:
The idea for the circuit is to fire a cold start injection valve on an old car. There is a separate Thermo Time Switch (basically a bimetal switch), which fires the valve for a certain period depending on how cold the engine is (4 - 10 seconds). But when the engine is HOT the bimetal circuit is open and then the valve is fired from a separate circuit for just 1sec. The original circuits are now nearly 50 yrs old Bosch units and most have failed and those that haven't (yet), are immensely expensive. Most people bypass, them with a crude switch on the dashboard, operated manually. I would like to automate the process, but try and improve on the original.
This why I want the PULSE and the low duty cycle.
Ignoring the Thermo Switch, assuming it is open circuit (i.e. Engine HOT)
A delay relay will operate with a 12v trigger, but the delay won't start until the trigger is released. If I use the cranking 12v supply, this will be ON, as long as I crank the engine, so the relay wont release until I stop turning the starter motor. This is a problem, as the valve will be operating during the whole start cycle and will flood the engine.
So, I thought, if I can operate the delay relay with a short 12v pulse, it will see the pulse, then as long as I set the delay for 1 sec, it will go off, hence only firing the valve for the required period. The reason for the low duty cycle is I don't want more than 1 pulse during cranking. It would be odd to be trying to start a hot engine for more than 10sec, in this instance there may be a separate issue anyway, if that makes sense ?
Please tell me if I'm trying to reinvent the wheel, I have limited electronic project experience !!