EcoTEC petrol: misfires & fuel-trim logic
A calm way to stop guessing: use trims, load and misfire counters to separate ignition, air leaks and fuel delivery.
What Vauxhall drivers report (and what it often really is)
- Hesitation / surge at light throttle → air leaks, PCV issues, MAF plausibility, or weak coil under low load.
- Misfire only cold → ignition (coil/plug), intake leaks that seal when warm, or coolant-temp/fuelling bias.
- Misfire only under load → coil breakdown, plug gap, fuel pressure, or boost leak on turbo petrol.
- Lean codes with no obvious misfire → small vacuum leak or MAF drift.
Quick workshop logic
1) Read trims properly
Look at STFT/LTFT at idle and at 2,500 rpm no-load. Then compare with trims under light road load.
- High positive at idle only → vacuum leak / PCV / intake gasket.
- High positive across the range → MAF drift, fuel delivery or exhaust leak ahead of O2.
- Negative trims → rich bias (stuck purge, leaking injector, over-reporting MAF).
2) Misfire counters beat “feel”
A mild miss can hide. Use misfire counters + load/RPM snapshot. If one cylinder dominates, treat it as a single-cylinder problem first.
- Swap coil/plug between cylinders to see if the misfire follows.
- If it doesn’t follow: compression, injector balance, intake runner leak.
Codes that commonly sit together
Use the AI tools the right way
Copy/paste your code list plus engine size, fuel type, mileage, and whether it’s cold-only / hot-only / load-only. You’ll get far cleaner guidance.
Open AI toolsTrust note: These profiles are designed to narrow possibilities. Confirm with test data (trims, misfire counters, pressure/smoke tests, voltage checks) before buying parts.