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Poor Power and Jerking


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#1 Ingah

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Posted 12 November 2009 - 10:29 PM

I was just hoping for ideas regarding a persistent problem with my girlfriend's car (unfortunately we aren't in the position where we can replace a large array of parts though - so i'm hoping it's something minor)
It's a 1.25L petrol, 'zetec' engine, Ford Fiesta Encore R-reg.

When the vehicle is started from cold (e.g. in the morning), it 'jerks' for want of a better word, and as a consequence accelerates slowly, in bursts, seemingly no matter which gear it's put in.
Also, on the motorway (when warm as we live ~10 miles of 30mph limit from the motorway), the car is just about OK going downhill, but when the car goes uphill, the 'jerking' starts again, and causes the car to lose speed, to about 50mph or even less. She finds that if she uses the accelerator in bursts (a few seconds foot down, and few seconds foot up - this has a less pronounced effect and the car is able to maintain a higher speed of around 60 to even 70mph). The theme is that she finds that if she takes her foot off for a few seconds, it almost recovers for a few seconds before it starts to misbehave again.

The car is old and has had this problem since it was bought - the spark plugs and oil and a few other bits have been renewed since she bought the car (we even tried a few doses of redex!), so we're quite stumped.

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#2 Fraser.

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Posted 12 November 2009 - 10:58 PM

Sounds like it could be one/both coil packs to me. Fairly cheap to replace so worth a try even if that isn't the cause!?

Happened to my old car (punto), same symptoms, coil packs cured it!

#3 stef123

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Posted 12 November 2009 - 11:54 PM

sounds like your engine is misfiring, the coils/coil pack are probably to blame

#4 ChrisZetecS

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Posted 13 November 2009 - 11:35 PM

Just thought I'd say on here rather than post a new topic... but these last few weeks my 58 reg Mk7 Zetec S 1.6 petrol has been jerking violently when cruising at around 30mph, no idea why. Anyway my car has done a little over 21k miles and will be due its 2nd service (25k) sometime early in the new year.. Is it worth going in to my Ford dealer now or waiting until it's next service??
Any suggestions what it could be? Like I say this happens when the engine is warm and cruising at 30ish mph, and seems to be happening more and more regularly.

#5 Ingah

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Posted 03 March 2010 - 09:53 PM

We've just managed to get the money together and had the coil pack and HT leads changed with those we found at our local breakers - but the problem is still there - and if anything even more pronounced at motorway speeds (more violent "jerky/jumpy" acceleration). However, the mechanic was able to spot a "throttle related" thing at the front of the engine compartment, a small flat board with 2 wires, red/black, coming off it - which were frayed/broken. So we had that replaced with one from the nearby breakers.

Note: The car has far better acceleration after this work was done (but as stated, the original problem is arguably worse!)

Mechanic seemed to want to plug the car into a diagnostic (am a little surprised this is possible with such an old car), but this is more money so we've decided to have that done later. Out of interest, what does the diagnostic for a car of this age actually do and check?

However, could clogged/damaged/old air filters be causing this problem? (The mechanic mentioned about the air flow and i've realised that the previous owner probably didn't do all that much servicing to the vehicle...)

#6 Catweasel

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Posted 05 March 2010 - 06:37 PM

I was just hoping for ideas regarding a persistent problem with my girlfriend's car (unfortunately we aren't in the position where we can replace a large array of parts though - so i'm hoping it's something minor)
It's a 1.25L petrol, 'zetec' engine, Ford Fiesta Encore R-reg.

When the vehicle is started from cold (e.g. in the morning), it 'jerks' for want of a better word, and as a consequence accelerates slowly, in bursts, seemingly no matter which gear it's put in.
Also, on the motorway (when warm as we live ~10 miles of 30mph limit from the motorway), the car is just about OK going downhill, but when the car goes uphill, the 'jerking' starts again, and causes the car to lose speed, to about 50mph or even less. She finds that if she uses the accelerator in bursts (a few seconds foot down, and few seconds foot up - this has a less pronounced effect and the car is able to maintain a higher speed of around 60 to even 70mph). The theme is that she finds that if she takes her foot off for a few seconds, it almost recovers for a few seconds before it starts to misbehave again.

The car is old and has had this problem since it was bought - the spark plugs and oil and a few other bits have been renewed since she bought the car (we even tried a few doses of redex!), so we're quite stumped.



#7 artscot79

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Posted 05 March 2010 - 07:15 PM

faulty pcv valve or faulty injector or the maf needs replaced if it has one

#8 L S Auto Repairs

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Posted 05 March 2010 - 10:10 PM

I was just hoping for ideas regarding a persistent problem with my girlfriend's car (unfortunately we aren't in the position where we can replace a large array of parts though - so i'm hoping it's something minor)
It's a 1.25L petrol, 'zetec' engine, Ford Fiesta Encore R-reg.

When the vehicle is started from cold (e.g. in the morning), it 'jerks' for want of a better word, and as a consequence accelerates slowly, in bursts, seemingly no matter which gear it's put in.
Also, on the motorway (when warm as we live ~10 miles of 30mph limit from the motorway), the car is just about OK going downhill, but when the car goes uphill, the 'jerking' starts again, and causes the car to lose speed, to about 50mph or even less. She finds that if she uses the accelerator in bursts (a few seconds foot down, and few seconds foot up - this has a less pronounced effect and the car is able to maintain a higher speed of around 60 to even 70mph). The theme is that she finds that if she takes her foot off for a few seconds, it almost recovers for a few seconds before it starts to misbehave again.

The car is old and has had this problem since it was bought - the spark plugs and oil and a few other bits have been renewed since she bought the car (we even tried a few doses of redex!), so we're quite stumped.


Have you tried carrying out a compression test to the cylinders?

If you've already had the spark plugs, HT leads and coil pack replaced you can't possibly have a missfire.

Although you could have a faulty injector.

I hope this will be of some help and please contact me for further assistance.

Edited by Gazjs, 06 March 2010 - 12:49 AM.
EDIT QUOTE BRACKET FOR EASIER READING


#9 Ingah

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Posted 23 September 2011 - 01:38 AM

Firstly, i know this is an old thread (i started it ;) ), but we never did get the problem fixed, car still isn't very happy from cold or on motorways. Although it's now able to do 70mph. Just about. Wouldn't say it's healthy though.

Girlfriend's finally got herself a proper job, so may soon have the money to fix this (in contrast to the situation of the last couple of years where her parents, paying for it, have been struggling to scrape together enough money for things like the tax), after she gets the cam belt changed of course (only worse than badly running car... is no car!)

Car's done ~25K miles in her ownership over about 3 years, it's now on a little under 90K miles (she's the only one in her immediate family to be driving, so many of those miles are ferrying others to town and back).

I changed the air filter in the intermediate time, and of course oil and filter has been changed a few times. Otherwise the car has merely had essential work done for MOTs on things like brakes and suspension components, along with a good amount of welding.

Have always had suspicion the plugs weren't changed though - a friend of a friend (apparently) did it with the plugs we provided a couple of years back, but we never were quite sure as he was the unreliable sort... Having bought a new set of plugs though, and them looking pretty easy to fit in the Haynes manual.. i guess i'll find out soon enough.

Car was plugged into a diagnostic machine at the local garage a year ago and apparently (i really should've got them to write it down as the family are hopeless at accurately relaying this sort of information to me), the lamda (oxygen) sensor was faulty. This said, the MOT just done a few weeks ago included a page of emissions results and it passed everything. CO was close to the limit (0.28% where 0.3% is the limit), but everything else on it was well within the shown ranges. They are in the habit of keeping this sort of paperwork now, so i can refer to it if needed.

TL;DR - how do i test the fuel injectors, as i suspect one (or more) must be faulty. And does the paragraph before this give anyone any additional clues as to what's up?

Edit: One additional thing, i can run a compression test if needed as i now have a compression testing kit. Not really wanting to do that though as i haven't done one before and prefer to learn and make mistakes on my bikes (i solely use motorbikes to get about), than on my girlfriend's 1 car.

#10 MRC89

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Posted 23 September 2011 - 09:50 PM

Has the fuel filter been changed recently as well as the air filter?
Spark plugs are really easy to do, get a spark plug attachment for a socket set, and simply unscrew like a bolt. You should be able to see wear/soot on the bottom of the plug, if it's excessive then it probably wasn't changed as you suggested, and could be the cause of your many problems.
P.S make sure when you change the plugs that the leads go back on the same plugs, or you'll change the ignition sequence!

#11 Ingah

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Posted 26 September 2011 - 09:30 PM

Has the fuel filter been changed recently as well as the air filter?
Spark plugs are really easy to do, get a spark plug attachment for a socket set, and simply unscrew like a bolt. You should be able to see wear/soot on the bottom of the plug, if it's excessive then it probably wasn't changed as you suggested, and could be the cause of your many problems.
P.S make sure when you change the plugs that the leads go back on the same plugs, or you'll change the ignition sequence!

No, fuel filter has not been changed... hmmm... how likely is it to be the cause?

#12 MRC89

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Posted 27 September 2011 - 01:20 AM

No, fuel filter has not been changed... hmmm... how likely is it to be the cause?


Not sure mate, though I suspect it's causing my power losses/jerking problems. Getting mine changed within the next few weeks. I'd of thought the fuel filter would of needed changing long before 90,000 miles in your case though.

#13 orcomma

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Posted 27 September 2011 - 07:41 AM

If not the Coilpack my next try would be the mass airflow meter.

Give it a clean with some brake cleaner.

Be careful with it though, its very fragile.

Failing that I would think it would be a HEGO sensor

#14 pouly

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Posted 28 September 2011 - 10:58 PM

hi if your air filter is ontop of your engine undo the screws and take off, your oil cap should be attached by a breather tube take of tube and see if it is gunked up.when filter housing isn off check the breather pipe coming from your carb into the engine and see if this is gunked up aswell like a white sludge clean these all out with brake cleaner reasemble and see how it goes.

i had to do this several times when i had a r reg 1.4 zetec sport hope this is of any help


regards paul

#15 orcomma

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Posted 29 September 2011 - 06:37 AM

...from your carb into the engine...

i had to do this several times when i had a r reg 1.4 zetec sport hope this is of any help

regards paul


lol. the 1.4 zetec (or any sigma engine) had fuel injection.

and this issue is with the 1.25, which has a wing mounted airbox

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