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ST170 Jerky Acceleration Between 2100rpm and 2800rpm


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#1 Jacko9966

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Posted 12 August 2009 - 11:49 PM

My ST170 has started to do some odd things when it comes to accelerating. At roughly 2100 rpm to 2800 the acceleration is not smooth at all but below and above that it seems fine.

Also when keeping a constant throttle position in between these revs the engine hunts and feels like you are constantly dabbing the throttle.

I have recently done a full service including fuel filter.

Am personally thinking its something to do with the variable intake manifold.

Any ideas? Need to get it sorted as it annoying the hell out of me.

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#2 Braders

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Posted 26 August 2009 - 02:14 PM

mine does exactly the same, i fort is was due to needing a service, obviously i was wrong, if anyone knows why it does this then please let me know :D

#3 stef123

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Posted 27 August 2009 - 08:19 AM

could it be a missfire?...

#4 Braders

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Posted 28 August 2009 - 05:58 PM

could it be a missfire?...

now u mention it yeahh i think it is, how do i !Removed! stop it!

#5 stef123

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Posted 28 August 2009 - 09:24 PM

mmm could be the pesky coil pack. this is exactly how mine started before it packed in for good.

if you are gonna change it though, i'd recommend you have a look on ebay as there are companies who sell genuine ones that have been debadged for about 30 quid delivered which compared to 101.75 from ford is pretty good. a new set of spark plugs would also be a must, genuine ones aint too bad priced at the dealers usually. mine were 14 quid but the guy gave me 6 discount.

#6 jasonst170

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Posted 29 August 2009 - 10:13 AM

mine did the same it's only done 26,000 new plug sorted it

#7 Jacko9966

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Posted 30 August 2009 - 08:41 PM

Hi Guys

Thanks for your advice, I will go and purchase a coil pack and try it later in the week. Cross fingers it works cos its starting to really annoy me.

Also going to fit some Eibach lowering springs at the weekend and look at doing the rear trailing arm bushes.

Does this coil pack look like the right one?

http://cgi.ebay.co.u...id=p3286.c0.m14

Thanks
Paul

#8 Braders

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Posted 31 August 2009 - 03:17 AM

Hi Guys

Thanks for your advice, I will go and purchase a coil pack and try it later in the week. Cross fingers it works cos its starting to really annoy me.

Also going to fit some Eibach lowering springs at the weekend and look at doing the rear trailing arm bushes.

Does this coil pack look like the right one?

http://cgi.ebay.co.u...id=p3286.c0.m14

Thanks
Paul

its doesnt say for a focus ST170, and the parts for the st170 engine half the time are totally different to that of a normal 2.0 zetec engine, for example ST170 uses different spark plugs to that of a standard 2.0...my point is i would make sure its okay first mate

#9 KevinKevin

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Posted 31 August 2009 - 09:47 AM

My new focus 1.8 Zetec does the same thing. Especially when you've got a cars full. Acceleration is jerky between 2000-3000. It's only 8 months old. What could be wrong with it?

#10 muza

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Posted 02 September 2009 - 03:24 PM

my st170 does exactly the same! more so in cold weather it seems... hence i havnt noticed it too much all summer but its bound to start again soon as it gets colder.

did you guys manage to sort it with the new coil pack/spark plugs?

#11 Jacko9966

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Posted 02 September 2009 - 10:45 PM

Ok bought the coild pack after confirming the part numbers are the same. Got it today and look identicle except for the missing motorcraft sticker (U can see the glue residue where it once was). Tried to fit it tonight but no luck, the torque bolts were done too tight and wrecked one of the heads and my driver.

Going to go get a new driver and tomorrow. I will have to remove the coil pack mounting plate to get more space to remove those blasted bolts (Thinking i might have to drill the wrecked one out).

#12 Jacko9966

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Posted 16 October 2009 - 07:42 PM

Quick Update.

Replaced the coil pack, no difference. Have also tried some fuel system cleaner after talking to some garages, this made it slightly better.

I now have no more ideas on what to do next, so any ideas are welcome.

In the mean time I have fitted some Eibach springs and bluefin onto my car, both I would highly recomend. The Eibach springs give a slightly stiffer ride but iprove the handling greatly and reduce the body roll in bends while the bluefin gives the car better throttle response and seems to be more urgent through the rev range. Definatly makes overtaking easier on the back roads where I live.

Oh and by the way I wrecked the old coil pack to get it out.

#13 thesilverfox

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Posted 04 November 2009 - 12:14 PM

Quick Update.

Replaced the coil pack, no difference. Have also tried some fuel system cleaner after talking to some garages, this made it slightly better.

I now have no more ideas on what to do next, so any ideas are welcome.

In the mean time I have fitted some Eibach springs and bluefin onto my car, both I would highly recomend. The Eibach springs give a slightly stiffer ride but iprove the handling greatly and reduce the body roll in bends while the bluefin gives the car better throttle response and seems to be more urgent through the rev range. Definatly makes overtaking easier on the back roads where I live.

Oh and by the way I wrecked the old coil pack to get it out.


Hi there,

I can see you're not having much luck, but I have one suggestion that has not been touched as yet.

When I had an ST170, I experienced some dreadful jerking/'loss of power' characteristics not too dissimilar to what you've described.

Firstly, I thought it was the inlet manifold runner controller (IMRC), as the solenoid is apparently known to disintegrate, being mostly plastic and whatnot. Then I thought coil pack. Then I wondered if the spark plugs were dodgy.

However, Ford had a good look and found out it was the fuel pump that was faulty - basically, I realised then that I only noticed the sluggish performance when the fuel was less than 1/3 of a tank - the pressure in the tank was obviously low and the engine was requesting the fuel and the pump couldn't keep up, resulting in embarrassing jerking when putting my foot down too hard (and often softly too).

Got it done under extended warranty, but Ford said it was around 200 plus labour normally - I'm sure it can be done cheaper though.

It might not be the cause, but it's certainly worth bearing in mind.

tsf.

#14 Jamo_SportsTech

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Posted 05 November 2009 - 10:16 PM

have you looked at the spark plugs? mine was missing badly.. like a tractor through all rev ranges.. some muppet pressure washed the plugs before i bought it and they were having a 1" deep bath lol! tested the HT leads?

#15 Jacko9966

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Posted 13 December 2009 - 04:37 PM

Hi there,

I can see you're not having much luck, but I have one suggestion that has not been touched as yet.

When I had an ST170, I experienced some dreadful jerking/'loss of power' characteristics not too dissimilar to what you've described.

Firstly, I thought it was the inlet manifold runner controller (IMRC), as the solenoid is apparently known to disintegrate, being mostly plastic and whatnot. Then I thought coil pack. Then I wondered if the spark plugs were dodgy.

However, Ford had a good look and found out it was the fuel pump that was faulty - basically, I realised then that I only noticed the sluggish performance when the fuel was less than 1/3 of a tank - the pressure in the tank was obviously low and the engine was requesting the fuel and the pump couldn't keep up, resulting in embarrassing jerking when putting my foot down too hard (and often softly too).

Got it done under extended warranty, but Ford said it was around 200 plus labour normally - I'm sure it can be done cheaper though.

It might not be the cause, but it's certainly worth bearing in mind.

tsf.


I have noticed it is doing it with a full tank as well and like the other person commented it does it worse in the cold.

It also does it now when you keep a constant throttle position between 2000 and 3000 with it being worse at around 2100.

Could it be the duel mass flywheel as my clutch's biting point is really high?

I think I have no choice but to take it to a ford dealer sometime and will let you know the outcome.

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