Ford Fiesta ST
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#562787 - 10/10/18 11:32 PM Bucking/Jerking
Seannymr200 Offline
Stranger

Registered: 10/10/18
Posts: 2
Hi all

Having an issue with my MR200 ST with as the title says, bucking and jerking. This happens when I let my foot off the accelerator. It is most noticeable at low engine RPM in 1st and 2nd. Less so in the higher gears at higher speeds but still noticeable. I canít crawl along in traffic without constantly dipping the clutch to prevent it looking like Iím a learner on my first lesson lol my engine was recently rebuilt after the crank had to be repaired and a couple of rods replaced along with various other internals. Previous to this I had to have my gearbox repaired but that was about 3 years ago and I had no issues after this. Throttle body is lovely and clean, I have no exhaust leaks (not that I could find). Iíve also tried resetting the KAM just in case it was a TB issue by removing fuses then leaving out for a while and then idling the engine for 10 minutes and then taking it for a short gentle drive. Iím thinking could it be a vacuum leak? Could it be engine mounts? Could it be something far more sinister (hope not). Or maybe a fuel delivery problem with the pump? Spark plugs were changed around 4000 miles ago. When the engine was repaired the battery would have been disconnected for a fair while would this have somehow affected the ECU at all?? Only other things Iím aware of are a quiet whining noise that starts just after the engine has found its idle point which increase with engine RPM. It also becomes more noticeable when I put things on like heated seats and the window/mirror heaters so maybe something to do with the alternator. The whining isnít the PAS. I had this replaced in January and the fluid is still pink and makes no noises when I turn the wheel. Plus I know what a bad one of them sounds like from previous repairs!

Any advice or info anyone could give me would be much appreciated.
Many thanks
_________________________
56í Fiesta ST
MR200 @ WR Davies
Black ST 500 Alloys

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#562788 - 10/10/18 11:42 PM Re: Bucking/Jerking [Re: Seannymr200]
_Jimmy_ Offline
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Registered: 11/02/14
Posts: 1197
Loc: Northwest
Mine has always been jerky when cold, once it's warm it eases.
Could it just be the sportier cams making it jerky at low speeds? Mine is a little bit troublesome in traffic.
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2005 Fiesta ST
Milltek non-res, Newman fast road cams, Fusion Fabs custom inlet manifold

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#562790 - 11/10/18 07:10 AM Re: Bucking/Jerking [Re: Seannymr200]
Seannymr200 Offline
Stranger

Registered: 10/10/18
Posts: 2
Hi
Thankyou for your reply. I donít know whether it would or not. It doesnít matter if itís hot or cold it still does it. I had the MR200 conversion done in 2013 and it didnít behave like this then and Iíve had no other mods. Like most people, I am dubious about taking it to my local Ford dealer and explaining it to them for them to come back and say I need a new car or something lol
_________________________
56í Fiesta ST
MR200 @ WR Davies
Black ST 500 Alloys

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#562794 - 15/10/18 01:41 PM Re: Bucking/Jerking [Re: Seannymr200]
YellowBadge Offline
MountooningTipster

Registered: 26/08/07
Posts: 11369
Loc: here
you can't crawl in traffic with MR200 anyway, prob need around min 10mph in 2nd otherwise the cams won't be happy. But sounds like after your rebuild it's worse, so I would look at that, timing perhaps needs checking, maybe get it on a rolling road and see what the data gives back fuel air etc.
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MR200 Stage 3 200PS
Evans Halshaw
Mountune Pro

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