T6 CXEB Engine - Stalls after 5 seconds when starting from cold

[dave-halt]

Hi all,

I’m new to the forum and hoping someone can point me in the right direction.

I’ve recently bought a 2016 T6 with the CXEB engine, and I’m struggling with an issue I can’t seem to pin down.

Symptoms: With all fault codes cleared, the van will start from cold and just about idle for around 5 seconds before stalling. Pressing the accelerator makes very little difference. It will do this 7–8 times, each time running slightly longer if I give it plenty of throttle. Eventually it drops into limp mode, at which point it will rev up to the soft limiter.

Fault codes in limp mode:

1. P029900 – Turbo/Supercharger Underboost
2. P029900 – Turbo/Supercharger Underboost
3. P023800 – Turbocharger Boost Sensor (A) Circuit High Input
4. P00AF00 – Turbocharger/Supercharger Boost Control “A” Module Performance

Driving behaviour: On the road, the van feels very flat until about 2900 rpm. At that point the larger turbo seems to spool and it finally builds boost. Manifold pressure stays at atmospheric until that same 2900 rpm threshold.

Work done / checks so far:

• Both turbos are new and spin freely
• N274, N529 and N75 valves appear to operate correctly
• Actuator tests show full and correct movement
• All vacuum/boost pipes are correctly routed
• Full smoke test carried out — no leaks found
• MAP sensor is the 3‑pin type: one ground, two 5V feeds (engine off)
• Fresh fuel and new fuel filter
• Primer pump delivering well, rail pressure over 400 bar
• EGR has been removed by previous owner and blanked with Darkside plates
• Cam timing is spot on

At this point I’m running out of ideas and would really appreciate some advice on what to check next.

Thanks in advance.

 

[PhillH]

Have you tried splitting the exhaust at the turbo incase the exhaust is blocked, heard this before

 

[Dellmassive]

My first though was blocked dpf/exhaust.

Have you tried running without the exhaust?

May be split from the cat?

 

[darkman884]

The small turbo is not producing any boost