Passat (B6) Hesitation

[manic_man]

Hi guys,

I was hoping for a bit of advice from people probably more knowledgeable than me.

A bit of history:

4 months ago I bought a 2008 B6 Passat 2.0 TDI 140 with 40k on the clock.

It was due a new set of injectors on a VW recall. It was also due a cambelt (VW is 4 years/90k miles on this engine) It also has a 2 year service plan attached to it (so a major/minor service and two MOTs).

A month after buying it I took it to VW who did the injectors, cambelt (and water pump) and the "free" major service/MOT.

Since then I have a problem in that after a while I get what feels like a slight misfire between 1.8k and 2.4k RPM. The problem is it only happens when driving in a certain manner, which just happens to be exactly my style of driving while in Manchester's traffic. It feels very much like you have rapidly let your foot off the accelerator (the revs dip and then pick back up).

I have taken it back to VW on numerous occasions who claim they cannot reproduce the fault, I have offered to go out with their mechanics,but I know that chances are as I have had to drive there, the car won't do it again unless I leave it standing for 8 or so hours (i.e the time it stands in the car-park at work). They made me pay a £57 diagnostic fee last time I took it to them as they say that nothing is logged on the cars computer and that they can;t find fault with their work. Obviously this has made me very wary of going back to them.

It's not to bad some days and it didn't happen before I had all this work done. The obvious candidate is the injectors I suppose, but being honest I am completely out of my depth other than I know its really annoying to be coasting along in traffic and suddenly get a large jolt.

If anybody has any thoughts that'd be great!

 

[chad116]

You may be better off posting on a passat owners site as you will most certainly get a better responce as it may be a fault witht he particular model maybe ?

 

[manic_man]

I'm pretty sure it has to be linked to the injector/cambelt work, but I need more info before I start to force the issue. I don't like to go into things uninformed if possible. It didn't do it before and now it does, I just wish the darned thing logged it as a fault when it happened!

I will re-post elsewhere, but this forum is full of very knowledgeable people and ultimately the VAG 2.0 TDI engine is very common seeing as it's found in Audio/Skoda/VW models across their respective ranges, so I'm hopeful someone might have the odd constructive comment.

 

[Firestar_3x]

Timing belt might be one tooth out, but that should lead to bad performance across most of the rev range, could be a boost leak, can you hear any air escaping?

 

[manic_man]

I have noticed that there is a noticeable turbo "whoosh" if you have the window down, unfortunately I live on a busy road so standing with my head under the bonnet isn't the easiest thing in world (trucks rumbling past at 40MPH just to your left!)

Thing is, I know turbo's can have a bit of a whine when they spool up/down, other than that there isn't really anything noticeable, and frankly the turbo "whoosh" could have been there before, I was still getting used to the car when it went in for all this work.

I am pretty sure that the idle is a little less smooth than it used to be, you can feel the car "shaking" ever so slightly, whereas before it was the smoothest diesel I had ever owned (oxymoron?) Though i wonder if that's my imagination looking for faults now. That aside, it pulls smoothly and cleanly through the rev range, this was one of the main reasons the VW dealer said it couldn't be cambelt related as they say what you say that it would be noticeable through the range.

It is literally a "cough" when the revs suddenly drop while you are maintaining (or slowly increasing) the revs, it happens in all gears, but is most noticeable when in a higher gear as obv you notice rev changes more then.

 

[Firestar_3x]

On idle you might not notice boost leaks, it's only when the boost pressure builds that it finds ways to escape.

I'd go out and check every boost pipe connection, give them a tug, it's also worth checking the turbo intake hose, check the connection between the air box and the pipe, if air is bypassing the MAF then you will get these sort of issues.

Another option is to put some lightly soaped water in a spray bottle, lightly spray around the pipe work and watch for bubbles.

 

[Dogbreath]

Has the fuel filter been changed?

 

[manic_man]

Thanks firestar, not completely sure where im looking, ill have a bit of a google first for some images and have a look when i can.

Fuel filter has been changed at the last service (i know this because it started to leak and i had to take it back, they showed me the faulty seal and said they put a new one in to replace the replacement!)

 

[Jwajw]

Passat misfire

Hello, just wondering if you managed to fix the problem as I have the exact same with my passat

 

[LeMson]

MAF?

 

[manic_man]

Hi, sorry I completely forgot about this thread!

Sadly I haven't fixed it no. The problem is its a very erratic thing, some journeys there's nothing, others I am kangarooing down the road towards the start of my journey...

I had it booked into VW a few weeks ago, however I lost my bottle as it didn't do it for 7 days before it was due with them. I could just see them saying "we have checked everything, couldn't find a fault, £57 please and then me having to argue till I was blue that I had already paid a diagnostic fee before and that this was the same issue...

I then went away for two weeks and it has done it a few times on my way to and from work in the past week.

Unfortunately I'm away for work for the next two weeks so will have to book it in when I get back (assuming it doesn't completely break on me while I'm away with it of course).

I just kind of wish there was something to go on. It doesn't smoke, it isn't rough, it pulls cleanly most of the time, the ECU doesn't log any faults, just every now and then, about 15 minutes into a journey, there is momentary loss of power at between 1800 and 2400 RPM, but only when accelerating in a specific way! It literally couldn't be more of an ass of a problem.

If you get anywhere please do let me know as I literally don't even know where to start as I know when I try and demonstrate it to a VW tech it simply won't do it...

 

[realscot]

sounds like you need a datalogger to monitor the fuel pressures to each injector and see if there's a drop in fuel pressure. It'd also be able to monitor airflow. Dunno if VW will be bothered to do this, probably just gonna read the codes.

 

[classicVin]

It does bug me when everyone thinks we just plug it in and read the codes and thats it! Really annoys me that people think this! But anyhow For our dealership, we would be offering for you to go out with our master tech and demonstrate the fault.

Did you have the vehicle before the cambelt / injectors were fitted? If so, was it producing the same fault?

Could possibily be the Belt Timming out slightly, or it could be that the injectors were not set up correctly / precisely. As its a Pd engine, the injectors are compressed So it provides a pumping action, they are compressed by the same kind of idea as an inlet / exhaust valve, where a camshaft + rocker arms would transfer the movement down onto the injector. At the top of the rocker arm there is an adjustment bolt where you set the injectors up. Setting them up is pretty easy, just turn the engine round to a position in which the injectors are fully compressed by the rocker arm (in the down position as if it were to spray the fuel into the combustion chamber). Then once the arm is fully down, undo the 18mm locknut, then inside the locknut is a 6mm allen key bolt in which the bolt is turned all the way till it stops (where the injector needle has fully opened to its stops) then back the bolt off 180 degrees, then torque the lock nut to 30nm.

Pretty simple to do, but its something that i would advise on getting checked because it can cause running problems if not set up correctly.

Don't Accept the car back until the problem has been re-produced with the master tech and then diagnosed!

 

[TRNC]

The fault doesnt exist, you are imagining it! (VW official line)

This is what VW told me about mine after many many hours of investigations, they have failed to find the fault but it appears on many of the 140bhp BKP engines. I went to VW customer services and complained, raised it with head office but they still cant find the fault.

It comes and goes, always in the same manner but intermittant, generally within a certain range of air temp and in set conditions but you cant "make" it happen.

Mine had settled down for nearly a year, then sadly it reurned a few weeks back - its a pain but remember its all in your head and doesnt really exist and you'll be fine!

 

[manic_man]

Well, out of interest, I disconnected the MAF last night and did a 10 mile drive. It felt a bit down on power, less "shove", however what power there was was silky smooth. I then reconnected the MAF and got the hesitation effect this morning.

Of course this isn't definitive, however I will be doing the journey that nearly always causes it to do it tonight, so have disconnected the MAF again and will try it without. Clearly it could be one of many things (or it may all just be in my head ), butthe MAF is a nice easy place to start.

classicVin: I owned the car a month before the injectors were changed and then it was another month and a bit before the cambelt (and a full service) was done. In that first month I can't say I experienced anything. The problem is, I hate dealing with the garage where I had it done, they are very smiley and keep that smile up even as they ask you for £57 to look at a problem you didn't have before they carried out work. Of course it COULD be a coincidence and my MAF could just have gone faulty, but it's pretty poor if it has in less than 45k miles and less than 5 years. My previous Renault was more reliable than that!

 

[NeverWinter]

I have this same issue occasionally on my 170PD, it happened before and after my injectors were replaced.

 

[LeMson]

I suggested MAF because I had a similar problem (though different car altogether), hesitation around 2K revs, kangarooed if I put my foot to the floor, until 3.5K then worked like it had no problem, though overall felt like it had less power.

Cleaned MAF.....which killed it (my film type can't be cleaned), bought another, plugged in, goes like a rocket again now

Do you know someone with one you could borrow and try it? Rather than forking out for one :X

 

[Dangerous Dave]

The EGR valve closes over those revs so it may be sticking slightly, I would get that cleaned or replaced as they are cheap, if it is not fully sticking it doesn't always flag a fault code. A good way to check for a sticking EGR valve is more smoke than normal out of the exhaust.

 

[manic_man]

I'll see what the journey home is like, air temp and conditions are obviously right today to produce the problem, and the journey itself nearly always seem to reveal the problem, I guess the stop-start traffic is just right to do it.

Ideally I'd like to drop this off at my local VW dealer, get in with a master tech, reproduce the issue and then have them tell me exactly what it is. Problem is, I just know that no matter how hard I try, it won't do it, and taking the time to do it is just a real pain.

I'll let you know how the car is tonight.

 

[chimponarope]

Had the same thing with my Octavia PD170, was in and out of the dealers, including leaving it with them for a week at a time twice. "We can't reproduce the fault and no one else has reported any problems" trotted out over and over again. I'll be trading it in for something else soon I think.