We bought a 2010 Fiesta 1.4 petrol (74kw) with just under 20.000 miles. It was driven by an old gentlemen (over 80 years old ) on relatively short trips and low speeds, but in general car was well maintained, regularly serviced and kept in garage.

As expected, car was initially a bit down on power so we did a full service where they changed oil and all filters (oil, air and fuel) and also checked/refill air condition. We also started to drive it at higher RPMs and on longer distances to "clear it" a bit.

What I found out is that there is occasional (every 5-10s) hesitation and/or short (0,5-1s) loss of power when accelerating under moderate/heavy load from 2.000-4.000 RPM. Above 4.000 RPM engine power really kicks in and car accelerates very well.

After around 1.000 miles I decided to change spark plugs and the engine is running smoother, but occasional lack of power/hesitation is still present.

Then I drove it for around 300 miles on highway at higher RPMs and speeds (unofficially over 105 mph with power left :) ) and I can tell that "all the horses are still in the barn", but they occasionally do not want to came out. I can tell that after highway drive, power delivery is improved, but hesitation is still there.

What I also found out is that if I put acceleration pedal all the way to the floor, there is much less or almost no juddering, acceleration is better, but power delivery is still not 100% up to 4.000 RPM.

What I did up to now?

I am using FORScan for OBD connection and there is no error code present. I checked both oxygen sensors, catalyst and they seem to work ok. What I found out is that when engine runs at idle, it runs a bit rich (long term fuell trim -8%), but when driving long term fuel trim drops to -3% which is ok.

Is there any idea where to start searching for solution to this problem? Did anyone have similar problems? I have some ideas, but I would not like to change parts that are not needed to change. Do you know any test for this kind of problem that I can preform with OBD scanner to narrow down possible causes? 

If needed I can share FORScan data of driving.

 

Thank you in advance for your help

Any ideas?

31 minutes ago, im2009 said:

Any ideas?

Check your plug lead resistance, one of them may be duff! Had a 'barely noticeable' hesitation for two years that annoyed the heck out of me, after changing plugs/air filter I swapped my fiesta leads with my sons from his fiesta and noticed the difference immediately, checked the leads and one was 'away'. £18 for a new set and it was sorted!

Thank you. I will try it.

26 minutes ago, im2009 said:

Thank you. I will try it.

Here's a link to a page explaining how to test .... https://www.ngk.de/en/technology-in-detail/ignition-cables/diagnosis/testing-of-ignition-cables/

On 16/08/2016 at 7:20 PM, im2009 said:

when engine runs at idle, it runs a bit rich (long term fuell trim -8%), but when driving long term fuel trim drops to -3%

MAP sensor can cause fuel trim errors. I am not certain if this car has a MAP (Pressure) sensor or a MAF (Flow) sensor, I think probably a MAP. Check this PID, it should match atmospheric pressure (corrected for altitude if needed) with key on, engine off. It should usually be 27 to 32 kPa at idle. (based on another car, but likely to be similar).

Major failure of the MAP will cause a DTC, but calibration shifts will not.

Ignition problems seem more likely to cause the mid range power problems, so check them (like Russ says) first.

 

 

Russ, thanx for test instruction. Will try it as soon as possible. If I understood correctly there should be more or less constant resistance on all plug leads per meter (they should be of different lengths).

TdciPeter:

Yes you are correct, I have MAP sensor. I already checked it once and did a quick clean with contact cleaner, but I will double check the values. I have calibrated pressure gauge on my smartphone, so I can compare pressure with OBD values.

Thank you again. I will report results.

Just an update on my hesitation problem. 

Due to bad weather and lack of time I was unable to check plug lead by myself, but I drove the car to my local mechanic for a check. He checked the plug leads and concluded that they should be ok.

He cleaned the throttle body instead and I must say that the car drives better. There is no obvious hesitation present, as there was before. I hope that this is permanent solution for the problem.

Thank you all again for your help. Your tips may come handy in following years, since, with my wife, we plan to keep the car for several years to come.

:)

I have the 1.4 petrol version which has the same problem. Mid range is terrible the car lacks power and grunt. Checked the ht leads and 1 &2 were alright but 3 &4 had oil residue in them which I cleaned and it made a bit of a difference. I then emptied half a bottle of brake cleaner into the throttle body which appeared sticky and the car wouldn't start to begin with and then got much better and actually felt a 30% difference on the overall drive. Decided to take off throttle body completely and clean both sides and in the process a friend noticed a breather pipe going from the intake manifold to the crank case (crank case ventilation pipe) which was sucked in this allowing no air to travel through the pipe. Managed to get the pipe today from Ford and to .y pleasant surprise power is back and fuel economy has improved somewhat so with a full service next week car should be like a rocket. So anybody with the same issue rather than spending hundreds on coilpacks, maf,tmap and the throttle.jody first check this pipe asnots and easy fix and such a small thing made such a huge difference! Hood kick to you all.

I would change the leads and coil pack