Hi all,

I’m looking for help diagnosing a severe loss of power / no boost issue on my 2015 Ford Fiesta 1.0 EcoBoost.

Background / work done

• Turbo recently replaced (old turbo compressor nut came off, lost power "shuuuup" noise like air being blocked)

• All boost pipes cleaned thoroughly and refitted and smoke-tested (no leaks found)

• Intercooler removed and thoroughly cleaned

• replaced oil and filter

• Replaced turbo genuine Ford refurbished turbo - Vacuum line to wastegate confirmed connected and actuator moves

• Car idles smoothly, no knocking or abnormal engine noise

• Oil level is correct

• Worked perfectly for 15 - 20 mins on first drive

Current symptoms

• Same symptom of when my first turbo went, sounds like air noise "shuuup" and loses power - was happening around 3000rpm 

• After the issue came back I run a log with Forscan - [url=https://postimg.cc/fVRKBvPP][img]https://i.postimg.cc/8zh0kKmT/Screenshot_2026_01_02_172433.png[/img][/url]

• Car has very little power, struggles to accelerate

• Cannot rev past ~2000 rpm under load

• Juddering / hesitation when trying to pull away

• When slowing to let traffic pass, engine stalled and oil light came on briefly and stalled, but went out immediately after restart

• ChatGPT suggested disconnecting battery for 15 mins then doing a "relearn drive" - was even worse after i done this couldnt even get to 2000rpm in gear 1. Then i had to pull in to let a car pass, oil light came on and car stalled, turned it back on and managed to get home oil light didnt come back on engine is at normal temp and sounds perfect on idle

FORScan observations -  [url=https://postimg.cc/fVRKBvPP][img]https://i.postimg.cc/8zh0kKmT/Screenshot_2026_01_02_172433.png[/img][/url]

• MAP stays around ~95–100 kPa (no boost)

• TIP pressure also ~100 kPa

• Wastegate duty cycles but boost never builds

• Throttle position and pedal position change, but ECU seems to limit torque

• Load stays low

• No active fault codes

What I’ve tried

• Battery disconnected to reset adaptations

• Throttle relearn procedure

• Gentle relearn drive (made symptoms worse — very low power)

• Verified vacuum supply to wastegate actuator

• Checked intake pipes and connections

• Engine idles fine after restart

Current behaviour

• Starts and idles normally

• Revving stationary feels a bit sluggish

• Under load it feels heavily restricted

• Feels like ECU is limiting torque / entering limp strategy

• No permanent warning lights

Question

What would cause ECU torque limiting / no boost with no DTCs on this engine?

Could this be:

• throttle correlation issue

• accelerator pedal / throttle disagreement

• misfire under load

• boost control plausibility

• protection mode after oil pressure event

• something else common on the 1.0 EcoBoost?

Any guidance on what to check next (specific sensors, relearn, or known faults) would be appreciated. It is driving me insane.

 

 

Sounds like the new turbo has died, possibly due to oil starvation caused by the turbo gauze filter being blocked, quite a common problem on the 1.0 Ecoboost.

18 hours ago, unofix said:

Sounds like the new turbo has died, possibly due to oil starvation caused by the turbo gauze filter being blocked, quite a common problem on the 1.0 Ecoboost.

I removed the feed pipe from top of turbo and can see its full of oil. the oil feed pipe was new aswell i know this is another filter but doesnt seem to be an issue because turbo has oil and power is intermittent which obviously it wouldn't be if turbo had died

There may be oil inside the oil feed to the turbocharger but how do you know that the oil supply is actually sufficient?

The only way to be sure is measuring the amount of oil at idle. Despite the lack of official oil supply specifications, the oil supply should be at least 0.3 Liter per minute. Anything less will be concerning. There is a big chance that the filter is at least partially blocked which drastically reduces the oil flow.

A turbocharger does not fail by itself. In 99,9% turbocharger failure has an external cause. Just replacing the turbocharger without investigating and solving what actually caused the failure is madness.

The locking nut of the turbine wheel also does not come loose by itself. I have only seen this happen when a turbocharger suddenly seizes at high speed. This specific turbocharger can run at very high speeds (248.000 RPM according to the official specifications). When the turbocharger seizes at high speed it slows abruptly. The resulting torsional shock overcomes the nut’s self-tightening effect, allowing the nut to come loose.


I would start checking the actual oil supply just in case. If this is fine, it can be ruled out as a possible cause of the initial turbocharger failure.

The fact that the oil light has come on at least once indicates a serious oil pressure problem. This engine only has an oil pressure switch that switches when the oil pressure is insufficient. At the moment the oil light comes on there is insufficient oil pressure and the engine should be stopped immediately (as far as safety allows).


When were both wetbelts changed and the sump/oil pump intake cleaned?