I have a 1988 Ford Fiesta 1.4 CFI as a cheap extra car. The car is in an excellent condition, but when accelerating at low speeds it hesitates. When it reaches about 3.000 rpms it accelerates without any problems.
I have renewed the following (low cost) components :
- Spark plugs (Bosch FR 7 DCX+) gap set to 1.0 mm according to Haynes manual.
- HT-leads replaced
- Distributor cap replaced
- Air filter replaced
I have asked at the local Ford dealer about the cause. Here it was suggested that it might be a vacuum leak, getting "fake" air to enter the inlet after the injection unit and thereby screwing up the mixture. This explanation sounded quite reasonable, but after inspection I have not been able to locate any leaks. I have also used some "start-spray" to see if the engine would increase it's revs when it sucked it in (this was recommended by the Ford dealer).
I think the reason might be incorrectly set gap on the spark plugs since it seemed like the problem got better when I changed the gap size from 1.1 to 1.0 mm. But I can't see why this should have any influence at low revs - I would expect it to be a problem at high revs if the gap was set incorrectly.
Another thought that crossed my mind is the capacitor for the ignition system. Can it be broken and would it result in a symptom like the one I have?
Any help would be highly appreciated.