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Engine & running faults

Car jerking when accelerating

Jerking under load usually means the engine is briefly not getting the fuel, air or spark it needs — live data while driving is the quickest route to the cause.

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Symptoms drivers describe

  • Hesitation or a kick when you press the accelerator
  • Worse under load, uphill or in higher gears
  • Engine light on or flashing at the same time
  • Rough running that settles at steady throttle

Possible causes

  • Worn spark plugs or failing coil packs on petrol engines
  • A blocked fuel filter or weak fuel pump
  • Injector faults or poor spray pattern
  • Air leaks after the mass airflow sensor
  • Turbo or boost control problems on diesels
  • A partially blocked DPF causing power limits

What you can do

  • Note the revs, gear and load where it happens
  • Mention whether the engine light comes on with it
  • Avoid heavy towing or long journeys until it is checked

How we check it in the workshop

We road test with live data logging, then test ignition, fuel pressure, boost and air metering to find the point where the fault appears.

Is it safe to keep driving?

Usually safe to drive gently, but a flashing engine light means stop — that can indicate damage to the catalyst.

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Related repairs

How we can help

Engine DiagnosticsEngine faults are usually a chain of events rather than a single broken part. We test fuelling, ignition, air, compression and control signals to find where the chain breaks.Read more Diesel DiagnosticsModern diesels combine high-pressure fuelling, turbocharging, exhaust gas recirculation and after-treatment. When one part of that system drifts, the symptoms usually show up somewhere else.Read more Injector Diagnostics & Injector-Related RepairsInjector faults imitate a lot of other problems. Testing the injector data before replacing anything avoids fitting expensive parts the engine did not need.Read more DPF DiagnosticsA DPF warning is the end of a chain of events, not the start. Finding out why the filter is loading up is the part that saves money.Read more

Engine & running faults

Other symptoms in this group

Car stuck in limp modeLimp mode is a protection strategy, not a fault in itself. The control unit has seen a reading it does not trust and has reduced power to keep things safe.Read more White smoke from the exhaustColour, smell and whether the smoke clears once warm are what separate normal condensation from a coolant or fuelling problem.Read more Blue smoke from the exhaustBlue smoke points at oil reaching the combustion chamber or exhaust. When it appears — start-up, overrun or under boost — narrows the cause.Read more Black smoke from a diesel exhaustBlack smoke is unburnt fuel. On a modern diesel with a DPF it usually also means extra soot heading into the filter.Read more Car losing power when acceleratingLoss of power is either a fuelling, air or protection issue. Live data under load is what separates them rather than guesswork.Read more Car cutting out while drivingIntermittent cut-outs are among the most important faults to record properly, because the evidence disappears the moment the engine restarts.Read more

Want this looked at properly?

Send us your registration and describe the symptoms — we will tell you what the next step is.

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