Persistent undertrack
Actual boost rose with the requested value (shape correlation 1.00) but stayed a mean 0.40 bar under it, and was still 0.53 bar under at the end of the commanded region. Largest shortfall 0.53 bar.
Don't fire the
parts cannon
- This sheet does not name a cause. A trace shape narrows the search. It does not end it.
- Nothing here says the turbocharger is at fault. On this shape it is the last thing to assess, not the first.
- Nothing here says the boost sensor is lying. A sensor problem usually reads implausible, not merely low.
- A remap will not recover air that never arrived.
Your log carries out one of these steps and rules out one more, because your engine does not have the part it refers to. It does not tell you which of the remaining four is the answer — nothing here can do that yet.
- Still to do
Pressure-test the charge system cold. It comes first because it is cheap, non-invasive and clears or confirms an entire branch of the tree in one test — not because a leak is the most likely cause. We do not yet have the case data to rank causes, and will not pretend otherwise.
- Done — by your log
Log requested vs actual boost through a full-load pull. The shape of the gap narrows the cause more than any single reading.
Actual boost rose with the requested value (shape correlation 1) but stayed a mean 0.4 bar under it, and was still 0.53 bar under at the end of the commanded region. Largest shortfall 0.53 bar. - Not on this engine
On a variable-geometry diesel, check the vane mechanism and its actuator for soot binding and sticking before chasing leaks — this is the leading cause on VGT engines and it does not apply to a wastegated petrol engine at all.
- Still to do
Check wastegate / actuator free play and travel, and the electronic actuator adaptation where fitted.
- Still to do
Inspect the diverter or blow-off valve for a torn diaphragm or a stuck piston.
- Still to do
Only then assess turbocharger condition — shaft play, wheel damage, oil carry-over.
- Evidence tier
- E1 — log only, no repair recorded
- Counts toward medians
- No — needs E2
- Raw file
- sha256 4f9c…a17e
- Channels mapped
- 5 of 5 used
- Units applied
- none — both in bar gauge
Assumptions: none. Where a pressure channel arrives in absolute units it is converted to gauge using standard barometric pressure, and that conversion is printed here rather than done silently — an absolute target compared against a gauge actual is how a healthy car gets a catastrophic verdict.
Your ECU asked for boost.
Did it get it?
Upload a full-load log. You get a sheet like this one, and a link you can paste anywhere.
Read my log