Spark plug problem
Q I would like your advice regarding a spark plug problem on our 2001 Ford Focus 1.6LX which has covered 17,000 miles. During the last 12 months or so, there has been an occasional misfire and on checking out the usual suspects, I found that one spark plug had been tracking with the usual tell-tale black marks on the insulator. The plugs were Bosch HR8MC+ fitted January 2018. Sometimes I would find two of the plugs with tracking marks.
The ignition coil was replaced September 2016 following a misfire on cylinder 2. I replaced the Bosch plugs with Motorcraft in January 2020 but the problem has returned. Tracking now on cylinder 4 plug.
I removed the HT leads which seem fine. Connections both ends are clean and bright and a tight fit on both plug and coil. I metered each lead with readings ranging from 2.8K ohms to 3.8 and 4.8 (2.8 being plug No. 4 – shortest). The parts guys at
Ford is quoting approx. £30+ per lead!
John Gravestock
A The tracking marks could in my opinion only be the result of a failing spark plug or the HT leads. As you have checked the HT leads and these appear to be good. Provided the rubber sleeve of the lead which fits over the plug is clean and dry then I would suspect the spark plugs.
My personal preference would be NGK TR5A-10 but at this stage having had the same problem return with two different sets of plugs then I would consider replacing the HT leads, although I would suggest a set of leads from the factors may be a better option. A set of competition level HT leads from this site https://bit.ly/cmuhtls is £58.50 which is a saving of 50%, a standard silicone set of HT leads starts from under £20 at this retailer https://bit.ly/cmlphtl
Providing the HT leads are clean and dry and there is no moisture in the plug area I would change the HT leads, but would add a cautionary note that one of the problems I have come across on this engine is that the core plugs between the 1&2 and 3&4 plugs can tend to become porous – when this happens the moisture will surround the HT leads and could cause the tracking you have experienced.