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Recently while changing my Mi16 engine from the Jetronic setup to the correct Motronic ML4.1 setup I had all sorts of problems with the ignition amps. After trying a couple of different brands, I still couldn't get the the car the rev without misfiring through the mid-range. At over £30 a go, trying different amps was getting expensive, so I decided to go DIY. As the Motronic ML4.1 ECU sends out a nice square wave on pin1 for the ignition signal, there's none of the signal conditioning that's needed for the distributor pick-up coil type ignition on the Jetronic setup. Therefore the ignition amp just needs to switch based on the ECU's signal, so something simple will do. A bit of research revealed the ISL9V5036P3 IGBT transistor is designed for firing car ignition coils, so I decided to base the circuit around one of those. I've attached the circuit diagram, and you can see how simple it is. Even with a nice metal box (which doubles as a heatsink) the cost of the parts is still less than the standard amps. The auto-reset circuit breaker is optional (Maplin sell them) as I wanted it in there just in case things went wrong. So far the amp has worked flawlessly over the past month or so. The engine revs smoothly and doesn't miss a beat. A vast improvement on the standard amps. So if you're struggling with unreliable amps, you might want to try this circuit.

I've just installed the Motronic ML4.1 loom on my 205 Mi16, after quite a few teething problems. I finally got round to taking her for a test drive and it wasn't perfect. Under gentle throttle it runs fine, the idle seems good and revs cleanly when not under load (i.e. stationary in neutral). However when I try accelerating hard it is very hesitant between 3k and 5k rpm, and I think it is more likely to be ignition related as the rev counter looked a little shaky (though it is difficult to tell). It does it all the time, so I don't suspect a loose connection. The coil is new, as are the HT leads, dizzy cap and rotor arm. The ignition amp is new too, but is an Intermotor one (is this likely to be a problem?). The AFM seems to give a smooth resistance reading when I move the flap, so I think that's OK.