2007 A3 8P 2.0 TDI Hesitation

[parko14]

First off, apologies for the looooong post. I have spent approx 30 hours researching this and have found masses of conflicting threads posts and resolutions hence why I am now posting my own thread after getting seemingly nowhere. I have added my full auto scan, with Advanced ID and the Log I took yesterday as attachments to this post.

Backstory:
I purchased a 2007 A3 Sport with BMN PD170 lump back in March after my PD130 MK4 GOlf was written off. Other than a few niggling issues that were easily resolved (passenger door mech, ignition switch, oil level sensor, brake pad sensor etc) the car was faultless and drove perfectly. No smoke, no drivetrain issues, no electrical gremlins. It was perfect.

Issues:
Then, in late April, as the weather started getting warmer, air temps above 15/16 degrees C, the car starts to hesitate between 1400 & 2000 rpm. Once you've passed 2krpm, it's fine and pulls hard. Once the car is warmed up, it generally does not happen. Researching this issue there seems to be a lot of disagreement on any forum over what the problem is. Some people swear it's the DPF, others the MAF, others the EGR valve, others say it's the EGR cooler and some claim it's the DPF pressure sensor.

Approx a week after the hesitation first started I got an EML. VCDS showed it was a lambda sensor issue. No problem, several hours of research later (it transpires the BMN uses an NTK sensor, not a Bocsh unit like every other VAG ever made?!?) and I got a new one fitted in under 40 minutes. Took it for a drive and no more hesitation. I put this down to the faulty o2 sensor preventing a DPF regen as its was only reading a static value. For the next couple of days, the car drove faultless again.

About 3 days later, the hesitation returns (turns out the ambient temperature had been a little cooler). Logging the o2 sensor, I confirmed that it was working as it was reading the AFR values and no more error codes have been logged in the 3.5 months for the o2 sensor. At this point, the hesitation has become more of a lurching or kangarooing, again, only between 1400-2000 rpm.

I have also done the following in an attempt to remedy the issue:

• Cleaned the MAF with electrical contact cleaner - Did not resolve the issue
• Cleaned the egr valve & ASV (this was horrendous inside) - Did not resolve the issue, though it was better yesterday
• Checked the intake connections - nothing loose or unconnected
• Verified the boost specified vs actual - at all measured rpm's the spec/actual are almost identical, especially in the trouble range of 1400-2000. This would rule out a boost leak as is common.
• Measured the MAF readings - approx 200mg/str at idle and rise to approx 450 at 2-2500 rpm - I'm not sure if this is right or not but I have had MAF issues on my old PD130 and it was noticeable through the entire rev range as a considerable lack of power - this is not happening here as I have loads of power after 2krpm.
• Full fluid and filter service with new fuel hoses from the filter to the hardlines to the cylinder head (perished).
• Logged the EGR duty,

In addition to the above, I have also taken logs of the DPF and this is where I start to scratch my head as I'm just not sure what is going on here.
The Particle Filter - Load Coefficient: this was at 0 for approx half of the log session, then jumped immediately to 20% and didn't budge.
The Particle Filter - Carbon Mass: reads 22.23 for the entire duration of the log (20 minutes)
The Carbon Mass - Learned Value: this was at -7.9 for the entire drive/log session.

Would the above be indicative of the DPF differential pressure sensor being problematic? I did look at it yesterday, and it appears someone has been in there before me as the retaining bolt is missing. I've not checked to see if it's a genuine or non-genuine item, but if the above readings are symptomatic of the DPF pressure sensor, then my assumption would be that it was never adapted, or that is a cheap crap one that has failed? Does this sound right?

The only error code I get is the one below:

008194 - Particulate Trap Bank 1

P2002 - 006 - Efficiency Below Threshold

Again, there seems to be a few trains of thought as to what this actually applies to but generally most agree it's either DPF (differential pressure sensor) or EGR cooler.
I do not suspect the EGR cooler as being at fault as the Exhaust Gas - Recirculat. (spec.) & Exhaust Gas - Recirculat. (actual) are fairly close. I have added a table below with a snapshot of the log I took yesterday.

Based on further up I would suspect this code is related to the DPF pressure sensor in my case, would anyone else agree?

My main theory at the moment is that the DPF is failing to regen, and at lower exhaust pressures, it's causing the hesitation. As soon I am over 2krpm, there is enough positive pressure to overcome the dpf restriction and it drives fine?

My secondary theory is that the EGR tends to shut over 2k rpm, and it is the EGR flow that is causing the issue (either too much or too little recirculated gas). Though since cleaning the EGR the issue still persists and I can see the EGR duty fluctuating over 2krpm in the logs.

Does anyone have any further insights or recommendations?

AdvID_AO57PZY-WAUZZZ8P08A059569-135306.txt AUTOSCAN_AO57PZY-WAUZZZ8P08A059569-217750km-135303mi.txt LOG-01-011-03E-418-687.CSV

[cliffcoggin]

That's a very detailed investigation Parko, to which I can add nothing. However your mention of a bolt missing from the DPF pressure sensor makes me wonder if DPF has been mapped out, thus preventing regeneration. Is it possible to tell from all your data?

[parko14]

That would make sense as to why certain dpf values seem static and don't budge. My other thought is simply that a prior owner cheaped out and used a non genuine sensor (I've still to take a look at it to see if it's genuine or not) which would also explain the values being reported.

 

If the dpf was mapped out, I don't see how this would cause the hesitation I'm experiencing unless it was deleted in the ECU, but the core was never hollowed out? If this was the case I would have expected more serious drivability issues at this point?

 

I also don't know what to look for in vcds to tell if the dpf was mapped out, though on the advance id log, it does say it was flashed successfully once, but wether than means it's the factory map or a remap, I have no idea.

[parko14]

UPDATE:

 

Yesterday I fitted a new DPF pressure sensor, adapted it then took it for a drive, attempting to do a forced regen.

 

At first, it appeared to work.

 

THe DPF load coeficient came down from 20% to around 6% but at this point the load coeficient went back to 20% and didnt budge. The pressure senor differential seems happy enought, fluctuating between 2mbar and 6mbar which is supposedly withing spec for a cleaned/new/unproblematic dpf.

 

During the drive, the exhaust temps never ecxceeded 550 degrees C, which as I believe, during a forced regen, the ECU will adjust fuel/timing etc so maintain exhaust temps of over 700 degreees C. this did not happen so I can only assume that forcing a regin, while VCDS accepted the command, the ECU did not start the regen process.

 

I can only summise that this is for two reasons:

1) the dpf has been mapped out/removed. The tail pipes are very black and sooty which I've been led to believe is a telltale sign of a DPF delete/removal.

 

2) there is something else that is preventing the DPF from regening. However, given that the DPF load is static at 20%, and this value has not changed since i purchased the car in March, I would believe that this is not the case.

 

The car still drives fine. VCDS shows that the specified/actual boost is correct and once the turbo comes on song, it pulls hard. It is just this hesitation between 1400-2000rpm that still persists.

I have today taken the manifold off, as I sal the swirlflap hole for the actuator is leakiing, so I've sealed that up, and I have also fitted a restrictor plate (I used an egr blank and drilled a 10mm hole in the middle) to restrict the exhasu gas flow into the intake. I've seen a number of people use an OEm Seat Ibiza egr gasket that from VW has a 9mm hole instead of the normal 25mm hole and they have all had good results.

 

If anyone has any additional insights into the above I would appreeciete the feedback.

I will report back on the jobs I've done today.

 

[parko14]

UPDTAE #2

On whim last night, I decided to unplug the MAF. I wasn't expecting anything here as the last time I had a MAF fail (on a PD130), the car had no power through the rev range.

Anyway, after work, I started the engine and unplugged the MAF. No audible change in the idle at all. Drove it for about 5 miles and the idle when stationary was rock steady. there was no stuttering, hesitation or lurching at all.

Normally, once the outside air temps are above 16-18 degrees, the idle is slightly bumpy, and the car is horrible between 1400-200 rpm as mentioned in the prior posts. Last night it was superb. It revved smoothly and delivered power evenly with no smoke or other issues.

Based on this, would it be safe to assume that the MAF is buggered?

I have the part number for my car, 074906461B (Bosch 0281002461), so getting a replacement is easy. My query though is after looking at some online, a large number of MAF inserts appear to have a resistor on one side, like the below image. My MAF does not have this resistor, so based on the fact that my hesitation/lurching tends happen when the air is warm, would this be something to do with measuring the air temp?

Either way, after many hours of research, a handful of hours in VCDS and 15 hours physically wrenching on the car, I think I may have cracked it.

Once I've fitted a replacement I will update.

[cliffcoggin]

Rob.

Your logic is sound, but above and beyond my knowledge so I can not comment. Do let us know the outcome.

[parko14]

UPDATE #3

I fitted another MAF. The car still hesitates, stutters and lurches in slow traffic, between 1400 & 2000 rpm.

I am now thinking that the issue is EGR related. When unplugging the MAF, I believe the ECU stops the EGR system from operating, so this may explain why the fault disappears when the MAF is unplugged.

In the last few days I have had the following fault codes pop up in VCDS:

001025 - EGR System P0401 - 006 - Insufficient Flow - Intermittent This code is due to the 10mm EGR restrictor I fitted a few days ago.

008194 - Particulate Trap Bank 1 P2002 - 006 - Efficiency Below Threshold - Intermittent I originally thought this was due to the DPF not regenerating. However, the code still persists after a new DPF pressure sensor and forced regen. Interestingly this code does not appear with the MAF unplugged so it may be related to either the EGR cooler or EGR Valve?

004711 - PD Unit Injector: Cylinder 3 (N242) P1267 - 006 - Regulation Range Exceeded - Intermittent I Have a new injector loom on the way as this was a common issue with the PD engines. I doubt this will resolve my problem but I might as well get this issue sorted.

 

Is there anyone who can offer any advice on this? I'm just going around in circles with this and getting close to just setting fire to the damn thing.