Ongoing misfire
QI have a 45,000-mile 2014 Ford Focus ST 250 that I have owned for the last three years – it’s got full service history before my ownership – but as with all big dealerships I have my doubts.
Under my ownership it’s had oil and filter service every 6000 miles done by myself using genuine Ford parts and a brake fluid change every 12 months (excessive I know but whilst it’s in the dealership for MOT we get a good deal). It also always has premium higher octane rated fuel and a regular dose of Cataclean, which I have used on other cars in the past with good results. Although using it on this car is more of a preventative measure than cure.
The air filter is a K&N performance panel filter which is inspected at every oil service and has recently had a brand-new battery of the correct type.
So, the car performs really well, pulls strongly and starts on the button.
However, it has always had a ‘lumpy’ idle – the first few minutes of a journey when cold it misfires making the car stutter. As the car warms up it seems to disappear. I believe Ford had issues with the earlier Mk3 Focus ST rough idling, which led to a Technical Service Bulletin issued to dealers about a wiring loom splice joint – if the customer complained fixed under warranty – though I am told my particular car is not in that batch.
The car went into my trusted Ford dealer for a lumpy idle issue soon after I purchased it and it had the Sound Symposer changed which made little difference to be honest. Otherwise nothing else was apparently wrong.
I have various methods of diagnostic reading tools, mainly budget auction site adapters that work via an app, but also a laptop-based unofficial Ford diagnostic software called FORSCAN, which has helped me out many times on various Fords in my family. None of these methods show any fault codes current or pending whatsoever, but although I’m not experienced in translating live data, I did use the misfire counter option on FORSCAN during a quick ‘from cold’ start to gather that the misfire registers on all four cylinders. My next step is to expand the live test duration to see how – or if – the misfires disappear.
The engine is a 2.0 turbo VCT Ecoboost and utilises over plug coil packs – though as the misfire is across all four pots, I am NOT looking at them to be the issue at this time. New genuine FORD (NGK I believe) plugs were changed at its last service.
Last year I had the car remapped by a very reputable nationwide company and the idle speed issue actually improved, but as the misfire issue was previous to the remapping I don’t think it has caused the issue. If no solution is found I may return it to the company for a diagnostic session, as they have all the latest Ford tools and whilst I was awaiting my remap to be installed, the Technician was actually advising a FORD dealership tech on various issues.
The car doesn’t use oil or water and the issue is one I could ‘live with’, as the car performs so well when warm, but I would much appreciate any advice you could give, so I could expand my skills on trying to locate any possible issue and fingers crossed fix it without forking out a fortune.
Many thanks for any assistance and please keep up the good work on CM. Steven Worrall
AYou mention that you are not experienced in translating live data, but there are a couple of readouts that can be checked easily. These are the air and coolant temperature. If any variation between the actual temperature and the temperature reading is apparent, you then have a good starting point.
If nothing seems amiss in that area, then you will need to move on to other areas. The Sound Symposer is an area that can be problematic, and some owners have chosen to delete the system by fitting a dedicated delete kit.
As the misfire is across all four cylinders, I think you are correct to disregard the possibility of a coil or even a plug problem, but this may suggest a fuel or fuel mix problem. Checking the fuel pressure supply you should have a low-pressure feed of between 3.8-6.2 bar and a high-pressure feed of 150 bar. These are readings that may be visible on your live data.
Even though you are detecting a misfire, as no codes are present, this often suggests a mechanical problem rather than an electronic one. Although I release that your ST is low mileage, I would suggest a compression check is carried out just to ensure that all is well in this department. If it is, this will at least eliminate any deeper problem with the engine.