(G) Possible cat prob

Hi all , my head gasket was replaced a month ago, when it went it missfired terribly, spluttering all over the place. Head gasket has been done, but ive been back to fiat about four times as the engine managment light keeps flicking on when driving at high moterway speeds, althought without any perfomance loss. Its due to go back to fiat this fri, but i am not confident they are going to fix it this time after already 3 attempts. So im looking at solving it myself. Do you think that the cat got damaged when it was missing so badly, i have heard that they do seem to get damaged but im insure how. All i can think is that perhaps fuel or water may have got into it. The car by the way is a "y" reg 1.2 8 valve punto. cheers

It needs the phonic wheel position to be relearnt by the fuel injection ecu. This is standard procedure when the crank pulley is removed. Check that the dealer has done it.

NumanR

Thanks for that, what does this do, the phonic wheel?

The phonic wheel is part of the crankshaft drive pulley, its teeth are the way the ecu knows the crank position. When the ecu is replaced or if it is reset the phonic wheel learn procedure is required to be done. This is done by revving the engine three times above 5000 revs when the engine temp is above 75 degrees. During the deceleration stages, the ecu memorises the wave pattern generated by the rpm sensor. This wave pattern is stored in the ecu as a reference to check for misfires. The ecu looks for incorrect acceleration of the pattern during power strokes, however if the crank pulley is removed and refitted it never goes back in exactly the same place and so the reference pattern does not match. This is sometimes interpretted by the ecu as a misfire, along with flashing light and an error code stored but no misfire felt by the driver.
This tends to occur at higher revs when the patterns timeframe is compressed, and so is more dificult for the ecu to interpret.
Resetting the ecu and carrying out the phonic wheel learn procedure puts a new image of the wave form into the ecu and will cure the problem.

NumanR