Mass Air Flow

[Taxiboy]

Since I bought my Passat B8 2.0tdi 150 in May last year I’ve not been happy with it due to various issues. Some were fixed however the car has still been annoying by been intermittently noisy, slow and just basically rubbish to drive yet would be nice and smooth during DPF regens and pretty refined. But now I have noticed poor fuel consumption over the past 2 months and getting a considerable bit less per full tank. I tried disconnecting both O2 and NOX sensors and there was no difference so that rules them being faulty. Also put injector cleaner in and still no difference.. However I have disconnected the Mass Air Flow meter and the car suddenly feels much faster, quiter and fuel consumption has improved too..
Does anybody know if replacing the MAF will solve my issues. For the time being I will have to reconnect MAF so the car can do active DPF regen. I was getting no fault codes either obviously until any sensors were disconnected. Anybody know if a faulty MAF can be faulty without any fault codes.

[Crasher]

Disconnecting the O2 and NOX sensor and that making no difference is not a test, in VCDS there are proper tests for them and for the AMM. Have you checked the DPF ash and soot loads?

[Taxiboy]

No I’ve not had it into garage yet. It does it’s DPF regens twice per full tank so that appears to be normal. Originally I did think it could have been an injector issue as the car felt sluggish and poor mpg but with the MAF sensor disconnected the car is much better so perhaps rule out the injectors.

[Mittens247]

Have you tried cleaning the MAF with electrical contact cleaner? What sort or mpg or range are you currently getting and how much has it fallen? Could some of it be winter related as mpg and range will detiorate in colder months. With no short journeys and just me driving, I was getting 55mpg/800 miles range in summer. In winter, the wife uses the car as well, as she likes the heated seats. With the added short journeys we are only getting 45-50mpg and about 650-700 miles range.

[Taxiboy]

I reconnected the MAF sensor and left it 2 weeks ago. Since then the car has driven better and mpg has improved and getting between 560 and 600 miles per tank which is better than before where I was lucky to get around 530 to a tank. It still has the tractor noisy engine/sluggish symptoms intermittently although not as frequent as before but it still annoying though. It also ran rubbish one morning last week when it was cold just noisy and crap to drive then once the outside temp went from 0c up to 4c it improved and was fine rest of the day. Might be worth cleaning MAF anyway.

[VAG-Abound]

Do you know whether it might have a rubbish engine remap on it? That could cause various problems.

Assuming not...

During regen the engine runs differently to get the exhaust temperature up. EGR off, altered injection timing, less air via throttle valve management and changed turbo pressure are the main things I think.

Has EGR system been checked? I don't know that type of engine, but if it is like ours a leak on the EGR pipes would let boost pressure out when the EGR valve opened for example. And that wouldn't happen during DPF regen if the valve was closed. Pulling the EGR valve control might help determine that.

Moving to harder work - I read an interesting thread elsewhere recently where it was reused / stretched injector bolts causing rough running. Has anyone checked injectors, their seals, injector loom (although it'd be unlikely for that to never play up during regen if it had intermittent breaks), etc?

[Taxiboy]

I wouldn’t have thought there would have been any remap done as car was bought with 30,000 miles on it and appeared to be ex company lease car.. The diesel specialist I took car too said injectors were fine and couldn’t find any problems. Considering it’s great to drive during DPF regen could well be down to the EGR. Due an oil change shortly and will ask for the EGR to be checked. But with no fault codes the garage answer is it would show up but will be saying it needs checked. Can the EGR valve control solonoid be disconnected? Would that keep EGR valve off/closed?

[Taxiboy]

Took the car to the diesel specialist and it is the glowplug that’s done. That explains the diesel knock mainly after I start from cold. Whether it improves the car overall I doubt it but never know. Also I wonder if a manufacturer software update might be worth getting done. Was told EGR valve is fine. After I cleared the pending fault code the car actually drove well all day.

[mickeybo]

Map sensor check 5v feed on tract 3 check the insulation between tracts 5 & 6 check tracts 2 & 5 if the voltage is not approximately 0.6vs plus/minus0.1 replace sensor these maf sensor plugs are a common insulation fault

[Taxiboy]

Thats for that I will give that a try. My Engine management light on this morning both pending and stored code from the Glowplug but also a pending code P20EE- SCR Nox Catalyst Efficiency Below Threshold Bank 1.. Is that an Adblue issue does anybody know?