Hi!

I bought used 2003 1.4 Petrol Fiesta few months back. It has 150k kms on the meter. I noticed that the engine is jerking when accerelating. Jerking occurs when revs are between 1 and 2k. Otherwise car is running well and its working fine on higher revs.

Earlier i noticed hissing sound under the bonnet. Sound came from evap system valve. I replaced the valve with new part. Hissing sound is gone and the car is jerking bit less now, but it still jerks. Another thing i have noticed is that when i open gasoline filling cap there is a hissing noise and slight pressure coming from the tank. Im suspecting that there still might be something wrong with the evap system.

Before i changed the evap valve checked fault codes and it there was fault code P1300: Boost calibration fault. There is no turbo in this car so i assumed it was because broked evap valve caused a vacuum leak.

I havent been able to read fault codes after changing the evap valve. Gotta borrow fault code reader from my friend.

I have also changed spark plugs, igniton coilpack and its wires, air filter, fuel filter and maf sensor. I Checked trhottle body visually and there was no dirt in there.

Any hints what the problem might be?

 

Fiesta jerks

yes, I've seen quite a few over the years 🤣🤣

31 minutes ago, unofix said:

Fiesta jerks

yes, I've seen quite a few over the years 🤣🤣

hohohoh😄

Bump

11 hours ago, Rieska said:

Bump

Have you got any new fault codes?

I also have a 2003 1.4.  It recently decided that it didn't want to idle steadily.  The thing that made by far the most difference was cleaning the fuel injectors.  I tried the thing that is normally suggested in YouTube videos, which is to spray carb cleaner through them while keeping them open (in my case with a spare car battery across the terminals to begin with, but eventually with a £30 injector pulser), but it was taking so long to come clean that I got an ultrasonic bath (lots to choose from, so chosen carefully) from Amazon and cleaned them in that.  I was, TBH, quite astonished at how long it took for the clouds of whatever it is that builds up in them to stop coming out of the ends.  In the end, they were in there for hours, but the difference it makes was, in my case, quite significant.  The output of the injectors has gone from a rather weak couple of jets to a nice fine mist, and the car seems much happier for it.

The sucking sound from the tank is normal - they are kept at negative pressure.

I don't think you have a MAF sensor, but a TMAP (or MAPT) sensor.

Ultimately, the jerking could be many things - poor compression, low fuel pressure, vacuum leaks.  They are more noticeable at low revs, since it is harder to keep the engine running at low revs.  See if you can use ForScan on it, with the recommended adapter.  O2 sensor output and fuel trims are good diagnostic indicators.