Loss of power
My daughter’s 2005 Ford Fiesta 1.4 Ghia has occasional driveability issues. The car has been in the family for 10 years because it used to belong to my mother and has covered 68,000 miles. It is serviced regularly by me and has new spark plugs every annual service – I decided the Ford interval was too long when I encountered a seized plug that snapped off.
The vehicle usually drives well, but every so often it will lose power and splutter, usually when the RPMS are below 2000. It doesn’t feel like a full-on misfire and unfortunately it does not record a code in the ECU or trigger the EML. There are also no pending codes. The only clues I have gathered are from a live data read, which showed the short term fuel trim momentarily going to 13 at a time when the car felt like it was driving roughly for a second or two.
The HT leads and the coil are all original and I will happily change them if you think it might cure the problem, but in the absence of a stored code, I was wondering if perhaps it was the crank or cam sensor causing the problem? Also, if you think it’s worth a trip to Ford for a dealer-level ECU interrogation, I’d happily do this. Alternatively, I could get it scanned by my friend’s Snap-on Solus if it would read the ECU better than my general fault code reader. Mark Thompson As you have a friend with a Solus scanner, I would first try using this to read the dedicated Ford codes and live data. You do not mention which code reader you are using, but if this is an EOBD unit you may well find something shows up with the Ford software. I have experienced surprisingly different data using the dedicated Ford software vs the EOB software.
The short term fuel trim is driven by the 02 sensor and this may be the source of the problem. Or it could be as a result of a weeping injector or manifold air leak causing the variance sensed by the 02 sensor. A fault code is normally only logged when the short term fuel trim exceeds 25%.
It would be worth checking the vacuum pipes around the engine to ensure that movement of the engine isn’t making one of the pipes leak. Similarly, a small fracture in one of the vacuum pipes could the issue. Such a small leak might be difficult to pinpoint, but you could try gently moving the pipes with the engine running and listening for an air leak.
A weakness in the HT leads or coil pack would usually show up when the engine is under a slight load, so for this reason I would not suspect them to be the culprit at this stage. Crank sensors can cause some strange faults, but hopefully scanning the system with the Snap-on Solus may reveal the cause.