Firend of mine has a cooper. The puncture light came on & he didn't know about the reset button so he took the battery off to see if it would reset. Now the car is only running on 2 cylinders. Any ideas??
The car had been repaired after a front end smash and ran fine.
The airbag light was on so the owner thought disconnecting the battery would reset it. After this it wouldn't run properly
I wasn't told at first at the same time he disconnected the 2 plugs on the ecu by the battery also.
I found that all injectors were working but only 1 coil, so cylinders 1 & 4 were firing only.
I traced there wiring back from the coil to the ECU (it changes colour)
The outtput from the ECU wasn't working
I opened the ECU to find that the plastic brackets inside that support the circuit boards had snapped (in the bump????)
The circuit board is a doubled over flexible on with double sided print & metal plates glued to it.
I spotted a rip in the board just beyond the edge of the metal plate close to were the external connector pins are soldered in.
The rip is shown in these blury camer phone pics - It looks here like a burn , but was a circular rip
The rip had broken the track that goes to the wire from the dead coil
I also noted that the soldered joints were other pins join the circuit board were loose so I resoldered them
The brackets were refitted using plastic glue
Result - car runs perfect.
My theory - the plastic brackets snapped in the crash.
Car repaired, ran ok.
Then when the ECU was unplugged I think as the plugs are very tight he had waggled them & as there were no brackets supporting the board the movement ripped it - thus missfire from then on.
Sorry about the poor pics, I didn't have my camera with me, & don't fancy opening it back up.