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Random misfire.

Help, Advice, Owners' Discussion and DIY Tutorials devoted to the second generation C70, S40 and V50 Volvos -- awkwardly model year 2004 ½ onwards -- plus where to go for advice and discussion on Volvo's sporty C30 Coupe powered by Volvo's ubiquitous inline 5-cylinder power plant.
Greenday694
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Joined: Thu Jul 11, 2019 3:58 pm
Year and Model: 2003 c70
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Greenday694

Random misfire.

Post by Greenday694 » Thu Jul 11, 2019 4:16 pm

Hello everybody. Volvo newbie here. My aunt bought a 2003 C70 convertible beginning of Last Summer. Never buy a convertible beginning of Summer , but she didn't listen. Paid top dollar. It is in good shape, new top, 130000 on the clock. First problem, antenna ring on the ignition switch. For preventive maintenance I did a complete timing belt water pump replacement. It was original. Ever since day one it would occasionally have random misfire, then all of a sudden clear up. Codes for random cylinder misfire and depending on which day, would have a code for one or two cylinders misfiring. Very rarely was it the same cylinders each day. 1 + 5. 2 + 5. 3 + 1. I replaced all five coils and plug. Seemed to help a little bit. But the problem still comes and goes. Sometimes when it will start misfiring the check engine light will blink. Later on I would check for codes , sometimes I would have misfire codes sometimes nothing. I've been a mechanic for over 40 years. This one has me stumped. The only thing I can think of is the ECU. Would really appreciate some help from anybody who has any suggestions at all. And if it is the ECU, does it have to be reprogrammed to the immobilizer? Thanks, Keith