My daughter has a 1600 Ford Zetec engined Fiesta with lowered body, sideskirts, air spoilers etc. Looks the business but it's like driving a plank of wood with an engine bolted to it! (She loves it though).
Recently it has developed a low speed misfire which causes stalling and sometimes stops it starting. After one breakdown we got it going again (not sure what we did but it started) and i followed her home. I noticed that using the indicators and brake lights caused a christmas tree effect on the rear lights. I knew that means an earth problem. (The car has non-standard triple circle light clusters fitted in place of the original).
Found the earth in the boot and it was loose. Tightened it up - and no more stalling! The trouble is it's a self tapping screw into the body so it loosens itself after a while and the problem comes back.
Why does an earth connection in the boot affect the engine? The engine earth strap is fitted and tight.
Any ideas?

 

Perhaps bad battery or alternator or something? Are you sure about the engine earth being ok? Have you tried fitting a second engine earth just temporarily?

 

Earth problems can be awsomely weird and wonderful, you can never have enough earth!!
In your case I would remake the earth to the ignition coil/ecu, as it sounds as though it is feeding/aquiring from rear light earth, components are clever and will try anywhere that is also conneted to earth for a supply.
tabetha

 

Thanks TurboShed & Tabetha. I was about to remake the engine earth but it started raining! I did disconnect the earth in the boot with the engine running though - and as I pulled the cable away there were some sparks (just before the engine died!). So there's a few amps going through it. Funnily enough, not 600mm away is another earth from the other rear light cluster which was tight. Next time I'll disconnect that one and see what happens.
Sorry it's only half the story but every time I go near the car it starts raining. Do you think God doesn't like Fords?!

 

It always rains in Hampshire doesn't it ?, used to go to Fleet a lot and always rained then!!
tabetha