[Rydawg]

Hello all, I'd appreciate some assistance as I'm at the limit of my technical ability with this one;

VW T5 2008 1.9L BRR engine.

Engine emissions light came on after the van stood still for 2 weeks (cheers COVID). This was accompanied by a huge loss of boost (like none) and the turbo isn't working at all. My N75 valve also went from mooing post shut-down to mooing constantly so the first thing I did was replace that (OEM part off ebay 1K0906627A), which stopped the mooing.

The loss of power and emissions light have remained.

I can't see any breaks/leaks in the pipes to/from the N75. When I take off the far right pipe I can feel suction when I put my finger over it. When I take all the other pipes off the N75 I can't feel a thing so, clearly, there is no suction going to the turbo to control the boost. I'm assuming the N75 is fine given that the problem started before I installed it and it's brand new.

Fault codes are P0299 (turbo underboost) and P0236 (turbo boost sensor A range/performance).

My thinking is that something is preventing the N75 from operating as it should and not sending anything to the actuator. When I carried out a freeze frame read I got a MAF reading of 0 (g/s) which seems wrong (not that I have a clue what I'm talking about). Could the MAF sensor be faulty and preventing the N75 from operating correctly?

Likewise, could the boost pressure sensor be a possible culprit?

I did wonder about the sticky vanes issue in the VNT, however when I move the actuator rod it feels smooth as silk and I can hear there's a good vacuum with air being pushed (or pulled, not sure) through the vent on the N75. I chucked some of that Wynns turbo cleaner in the tank for good measure, but I'm sure that was a waste of money.

Am I on the right tracks or has anyone got any other ideas?

TIA.

 

[Bennymassive]

Did you clear the fault codes after fitting the N75 solenoid?

Only time I have seen a MAF reading 0 (with the engine running), is when the pipe from the air filter to turbo has come off the turbo. Check that it is attached and there are no cracks in the air filter housing or pipe. You could also check the wiring to the MAF.

A Faulty (or dirty) MAP sensor or damaged wiring to the MAP sensor or problem with the N75 or lack of vacuum to or from the N75 will all give those symptoms, as will a duff turbo. You really need VCDS and a vacuum gauge to diagnose.

 

[Rydawg]

I cleared the fault codes, but sadly that made no difference and the light just came back on. I've checked all of the hoses/piping as best as I can and everything seems fine. I think you're right and this level of diagnosis is beyond me, it might be a trip to the garage...

 

[bluezie]

Are you getting any black smoke from the exhaust? If so it's very likely to be a boost leak, if not, then I think it's a job for VCDS to dig further.....

 

[T5 TDI]

Assuming the engine was actually running (have a look at the RPM on the freeze frame details) it could just be a dead MAF. Dead MAF's don't always give MAF related fault codes. If it was me I'd do the crude old fashioned test and see if taking the multiplug off the MAF improves the problem. When the ECU detects the disconnection it will use a 'best guess' for the airflow which won't be perfect but better than an erroneous zero airflow measurement so you should see some improvement.

If the MAF is connected but not reporting, then the performance will be dreadful right through the rev range so you will be crawling away from the lights not just when you might be expecting the turbo to kick in.

 

[Rydawg]

Are you getting any black smoke from the exhaust? If so it's very likely to be a boost leak, if not, then I think it's a job for VCDS to dig further.....

No black smoke at all. In fact I'd say that (aside from the lack of boost) it's driving completely normally.

 

[Rydawg]

Assuming the engine was actually running (have a look at the RPM on the freeze frame details) it could just be a dead MAF. Dead MAF's don't always give MAF related fault codes. If it was me I'd do the crude old fashioned test and see if taking the multiplug off the MAF improves the problem. When the ECU detects the disconnection it will use a 'best guess' for the airflow which won't be perfect but better than an erroneous zero airflow measurement so you should see some improvement.

If the MAF is connected but not reporting, then the performance will be dreadful right through the rev range so you will be crawling away from the lights not just when you might be expecting the turbo to kick in.

That's cleared things up slightly actually. I checked the figures again and the RPM also reads 0 so I presume that the figures I was looking at aren't actually any help at all.

I'll have a go at disconnecting the MAF and see what happens. Thank you.

 

[Bennymassive]

Worth checking the MAF, but your reading for the MAF was taken when the engine wasn't running and it will therefore always read 0, as no air is being drawn across it, so may be a red herring. It would be worth pulling at the MAP sensor and checking whether it is covered in oil and debris. Also, if coolant has come out of the reservoir it end up on the MAP sensor and can damage it or the wiring. One of your fault codes is saying the values from the MAP sensor are out of range.

 

[T5 TDI]

I doubt if it will help in this case then. Since you had the P0236 (turbo boost sensor A range/performance).
it could be a faulty (or fake N75). If you can get access to registered VCDS diagnostics you can make it operate the turbo actuator through its full range with the engine still at idle. Make sure the pipes are round the right way btw..