NOx emissions to high on 1.6 tdci

[TomsFocus]

 

On ‎02‎/‎09‎/‎2016 at 11:31 PM, Tdci-Peter said:

Made my day, that has. . Wish it was that simple!

It kind of is...  You just use the ABS sensors to tell the ECU the wheels are stationary, and add a 'clean' map for that situation!  

 

As for the DPF's, the cordierite ones can melt so I've read.  But it's not just about the material, its also about the number of holes in the core, the filtration, the sealer cement used to fix the block, the cat flow rate etc.  I can't say which of those 2 would be best, I bought a 'cheap' (£200) one that was rubbish and only lasted 3 months.  I would only go genuine if I had to again, the costs are ridiculous though.

I still agree with Simon, I'm still yet to see a car with a smashed through DPF fail the smoke test so I reckon the issue is elsewhere.  BUT that's not to say the DPF isn't now ruined by the excess soot as well...

[Tdci-Peter]

2 hours ago, Tombech said:

I do have the evo S filter laying in my garage, ready for mounting but I just wanted to be sure this was the right filter, now that it is more expensive! 

Just double check it is the coated type. If your car does not have the Eolys system (with an additive tank under the car near the fuel tank), then it needs the catalytically coated dpf. (cDPF).

One site I saw (buycarparts.co.uk) did say the 93098 was coated. Could not find it in the Walker catalogue though.

The Danish particulate test limit is almost 3x lower than the UK one. The readings you are now getting (down to 0.82) would easily pass in the UK. Whether the remainder is excess smoke from the engine, or failure in the DPF, I can not tell.

I assume you have checked the obvious things like leaks in the intake system. They can cause excess smoke. I think you did say you had checked & cleaned the EGR system.

It may be academic now, but I would be interested to know if cleaning the DPF reduced the DP over the filter at all?

With a smoke reading that low, I think I would try that Dipetane additive (may be just snake oil, but there is little to lose), give the engine a good, high speed, high rpm run to do some passive regen, then re-test. There may be residual soot in the dpf that has been disturbed, and will burn off. If that fails, change the dpf. If that works, then next year is another year, you will be older, but hopefully wiser (at least about dpf problems!).

 

 

[Tombech]

Hi

The washing of the current dpf filter has lowered the opacity with about 0.1~0.2 m-1 so that is at least something. It has also lowered the DP somewhat, as I remember from before the washing the DP was about 13kPa during drive with almost 4k RPM. Now the DP was 11kPa during a testdrive with 4k RPM. For some reason the preparticulatefilter temperature is showing constant 103 degrees, even when I unplug the sensor. This is wierd to me that the ECU does not show any errors there. hmm... I guess this fixed temperature also disables the passive regen of the dpf.

I have looked but not found any leaks in the intake system, however I am not quite sure how to do this properly, does a guide exist for this procedure? Can I use pressurized air into the inlet and see if it exits somewhere in the air line? 

When I cleaned the EGR valve, I could see the valve had been leaking on the thin metal seal plate between the EGR valve and engine. In one side the entire seal was black and the bolt holding the EGR to the engine was not tightened very well. Upon refitting I installed a new seal and cleaned off the black soot from the engine as best I could only using EGR cleaner spray and a towl. I was not sure about using sandpaper to abbraid it (I didn't want small sandcorns to enter the engine). But maybe this fix was not good enough and therefor the EGR it still leaking. But as far as I understand, the EGR valve is closed during the opacity test, so I guess this should not have an impact on the smoke..

I just stopped by the local car inspection guy to do another test, and the opacity was at bedst 0.92 m-1. He told me that he was 95% sure this problem would go away if I changed the DPF, so yet again I am confused about what to do! 

Best,

Tommy

[Tdci-Peter]

3 hours ago, Tombech said:

preparticulatefilter temperature is showing constant 103 degrees, even when I unplug the sensor.

I have been told that the lowest temperature that this sensor can read is about 100C. It should rise once the engine is running though. If it is a simple two wire thermistor sensor, then these read very high resistance when cold, so it could be that the ECU can not tell the difference between a cold sensor and a disconnected one. But I would expect it to flag an error if it stayed reading 100C with the engine running.

It would certainly prevent an active regen (when the ECU artificially raises the exhaust temperature while driving) if that sensor was faulty. Passive regen can happen any time the DPF gets hot enough in normal use, but is probably rare unless deliberately driving up long hills (or towing a large trailer) at 4000rpm & high throttle opening.

Re Hose checks, usually it is done by sight & feel. Visual check of all that can be seen, feel round the back of all ducts & hoses, squeeze the hoses to find splits. Pull at all joints. Some of the hoses & ducts are fairly easy to remove for better inspection. The intercooler is harder to check, but major leaks here are less common, and tend to be audible. A pressure test would be a good way, but needs blanking plugs at both ends (turbo to inlet manifold), and do not exceed 20psi (1.4 bar).

I can not think of any way tiny leaks around the EGR will cause smoke. It needs a leak of at least a few percent of the engine air flow to imbalance the mixture.

I think the DPF is basically knackered, the DP improvement from cleaning is barely significant. Whether it is worth trying the extra attempts I suggested in my last reply, or just replace it now, is up to you, really.

 

[Tombech]

Hi all

There has been some development in the case :) I looked for leaks on the inlet side, however I could not detect any. I unplugged sections and used pressurized air to test without any leaks. 
Then I cried for a while and afterwards decided to void the packing on the 800£ particulate filter and installed this in the car. I could smell a change in the exhaust of the car, it somewhat smelt "nicer" maybe even more fresh (Ok, I admit it was a long night and I needed the car to go to work the day after, so my judgement MAY have been compromised).

Today I drove by the car inspection and plugged in the car to the tester and what do you know, the opacity was not detectable, reading 0.00! I took my receipt and now I can drive the car for two more years before the next MOT. I am now aware of the needing for "thrashing" the car on the highway sometimes (Honey, I really need to drive fast, it is to clean the car you know, absolutely not because it is fun! )

The only thing I am a bit worried about is the temperature reading of the "pre particulate filter temperature" in forscan. It still shows a steady 103 degrees and does not make a sound if I unplug the sensor?! If i connect my ohm meter to the sensor the reading is high about 6MOhm and drops fairly quick to ~4MOhm when I hold the sensor in my hand. So there is definitely something still working, but I do fear I need to replace yet another expensive part (about 80£ for the darn thing, and there is two!) I cant access the temperature of the other sensor located after the DPF, however it has the same high resistance readings.

Do any of you know where I can find a lookop table for sensor resistance vs temperature?

Good day to you all

Best,

Tommy 

[iantt]

Temperature (°C)	Resistance (ohm)	Voltage (V)
-40	460467979	5.000
-20	102719922	5.000
0	28547913	5.000
10	16106769	5.000
20	9449513	4.999
50	2326245	4.998
100	371255	4.987
150	91432	4.946
200	30282	4.840
250	12389	4.627
300	5924	4.278
400	1772	3.196
500	724	2.100
600	363	1.332
700	207	0.857
800	131	0.579
900	89	0.409
1000	64

[iantt]

not sure that table is exacly for your egt sensor but should give some indication of temp v resistance

[Tdci-Peter]

17 hours ago, Tombech said:

Do any of you know where I can find a lookop table for sensor resistance vs temperature?

Ian does!

What I would add is that due to thermistor tolerance, the values below 100C will vary a lot from unit to unit. The device will be specified somewhere in the 250C to 400C region (10kohm to 1kohm), with a widening tolerance on each side.

Testing at about 100C is best, the steam from a boiling kettle would do, if you can remove the sensor. I am sure it can withstand steam for a few minutes, exhaust gas will be a lot worse than that. The readings you got may just be leakage currents due to oil & dirt. Lots of things (including you) conduct up in the Megohm region.

[Tombech]

Thanks.

It seems like my sensor is within the correct resistance range compared to the table. So I went for a detour on my way home from work today and what do you know, the temperatur reading was working, about 220 degrees after a 45min drive. I guess I was not patient enough to wait for the increase in temperature after the DPF was mounted. I was sure that the exhaust gas would rise the temperature ASAP in the inlet port of the filter - but I stand corrected :) 

I would like to thank you guys (and girls) for the help and support! I really appreciate this! 

All the best,

Tommy