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

 

[dave-halt]

A little update!

Spoke with a local ex VW tech, explained all and he said the high pressure fuel sensor will be faulty. Seen this before where the incorrect readings are being sent to the ECU, improper adjustments to other sensors/metering's are then instructed!.

Bought both and swapped them out.

Interestingly, the symptoms have now changed!

Starts almost fine, but then stalls after 2 to 3 seconds and where as before if you did 7 - 10 cranks/starts it would eventually go into limp mode and rev to 2.5k (hardly any power for driving).

Absolutely no error codes present, pending or otherwise.

Fuel pressure both actual and commanded are almost the same when it runs for a couple of seconds.

Tried the spare key to see if one had a transponder issue, but both work the same. In fact, if I sit inside the vehicle and lock it with the key fob, then crank for a start, it does the same, starts and stalls after 2 to 3 seconds. No icon on the dash suggesting the immobiliser is active etc.

Other than no icon on the dash, it almost suggests it's now an immobiliser issue!

Does anyone have any input on this please. Thx

 

[Bigsidavies]

Did you disconnect at the dpf as suggested by 2 people above?

 

[dave-halt]

Did you disconnect at the dpf as suggested by 2 people above?

Thanks for your reply.

No, pre and post pressures appear to be Ok, plus no sign of any DPF related codes.

 

[Bigsidavies]

I'm sure I've read posts where a blocked dpf has caused this issue and there were no error codes. No expert, but just going off anecdotal stuff on here. It would be an easy job to eliminate that by just disconnecting the exhaust and starting the van.

 

[dave-halt]

I'm sure I've read posts where a blocked dpf has caused this issue and there were no error codes. No expert, but just going off anecdotal stuff on here. It would be an easy job to eliminate that by just disconnecting the exhaust and starting the van.

Thanks again, I will give this ago and report back.