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    Renault Laguna 1.6 16v 2002 - Rough Idle and misfire - Fixed # Archived Message

    Posted by Jonathan Fry on August 13, 2009, 10:19 pm

    I've spent much of today on a Laguna, sold by a car dealer and returned to them under warranty.

    The symptoms include rough idle and what appeared at first to be a misfire.

    5 DTC's were present in the ECU which I've recorded and then cleared. They didn't return even though the symptoms continued.



    I removed the spark plugs to find No 1 cylinder plug looking like it had just been taken out of the packet and Nos 2, 3 and 4 plugs black.

    All 4 cylinders were compression tested with the plugs out and throttle wide open. No 1, 2 and 4 were at 200psi and No 3 was at 175psi.

    After refitting the plugs I disconnected each coil-on-plug (COP) multiplug in turn and each seemed to have a similar effect on the engine.

    I then disconnected each injector multiplug in turn. Disconnecting No 1 had no affect whatsoever on the engine but Nos 2, 3 and 4 all had an obvious affect.

    I removed the fuel rail with injectors attached and cranked the engine to see the injector spray pattern. All 4 injectors had a good spray pattern.

    I'm puzzled at the moment as to why disconnecting No 1 cylinder COP multiplug has an effect on the engine but disconnecting the same cylinder's injector multiplug has no affect at all. I have a feeling I'm missing something obvious here. can someone please throw some suggestions at me

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