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> MoT fail on emissions - diagnosis?
JeremyG
post 20th October 2016 22:42
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My 146 is now clear on its Mot, apart from the emissions, as follows:

Fast idle:
CO = 0.56% [should be =< 0.3%] = FAIL
HC = 78ppm [should be =< 200ppm] = PASS
lambda = 1.011 [should be between 0.97 and 1.03] = PASS

Second Fast idle:
CO = 0.44% [should be =< 0.3%] = FAIL
HC = 98ppm [should be =< 200ppm] = PASS
lambda = 1.011 [should be between 0.97 and 1.03] = PASS

Natural idle test:
CO = 0.50% [should be =< 0.5%] = PASS

MoT test centre say it's probably the cat; reading this forum I'm not so sure... what should I try first to troubleshoot this?

Car is a 1.8 with 101k on the clock. MAF is genuine Bosch. I do not know when the MAF or lambda sensor were changed.

I have MultiECUScan and will be connecting this tomorrow - any suggestions on what to check?

Cheers
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JeremyG
post 21st October 2016 11:02
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Ran the car up and monitored lambda values on MultiECUScan this morning.

Lambda voltage constantly cycles between 70 and 800mV, as per the graph below, with the "Lambda sensor status" constantly cycling through all the available values... Can anyone tell me if this is normal behaviour?

cheers!

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This post has been edited by JeremyG: 21st October 2016 18:15
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JeremyG
post 21st October 2016 22:39
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... and here are some traces for the MAF.

With the engine warm, I raised engine revs from tickover to approx. 3000 rpm. Air quantity and airflow meter signal both rose proportionally.

However - as revs increase, the actual air quantity is much higher than the desired air quantity.

As revs return back to tickover, actual and desired air quantity equalise.

Is this normal behaviour for the MAF?

cheers,

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This post has been edited by JeremyG: 21st October 2016 22:42
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GialloEvo94
post 22nd October 2016 00:27
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Did you give the car an Italian tune-up directly before the MOT to get the CAT nice and hot? More often than not, this solves high CO issues on the TS engine.

Regarding your graph, first observations are that there doesn't seem to be a lot of voltage activity going on with your MAF.

The following post shows a MAF trace I did a on mine a few years back. The bottom graph in that picture is for a brand new MAF running at idle speed only...

http://forum.alfa145.com/index.php?s=&...st&p=194115

If you look at post #12 in the same thread you will also see another graph showing the sort of signal you should expect to get from a brand new Bosch Lambda sensor.

EDIT: On second looks, your graph is at a different scale to mine on both the X and Y axis but there still seems to be less vigorous activity going on with your airflow signal. Maybe it is worth setting all the same parameters on yours as I used on mine (the same 4 with the same colours) and just running your car up to full engine temperature, then at idle speed only to see if you can get any sort of comparable graph to mine.

This post has been edited by GialloEvo94: 22nd October 2016 00:49


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JeremyG
post 22nd October 2016 21:05
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Thanks, that's an interesting and informative thread...

My investigations today went as follows:

1) Run another set of baseline stats, using the four MAF-related parameters you used in your investigation, at tickover with the car warm

2) Remove and clean MAF; then re-run stats

3) Perform ECU/idle actuator reset; then re-run stats

The results were as follows:

Little changed between 1) and 2):

- Average MAF voltage and range were pretty much unchanged - average 1.35V; range 1.23V - 1.45V
- Desired air quantity was running higher than actual air quantity - by an average of around 2kg/hr (or 25%) compared with actual air quantity
- Over 500 data points recorded in each sample

The discrepancy between desired and actual air quantity led me to perform an ECU/idle actuator reset.

This made quite a difference:

- Desired air quantity was much more closely matched by actual air quantity - average delta reduced to just 0.02kg/hr
- MAF output voltage (average and range) was the same as above

On the road, the car drove MUCH better - pulling harder and more smoothly than previously - result!

So, I was about to set off for the MoT retest when I started to get cooling fan errors on the engine ECU...

After a few more investigations, full speed on the fan works OK, but low speed doesn't - and it looks like the resistor in the fan housing has failed (no conductivity at all).

Anyway, I guess this has been the case for a while - so no idea why the engine ECU errors have just started.

Also discovered the fan housing is connected to the radiator by only one of its three screws... hmmm.

Will fix this tomorrow, then head down for a retest first thing Monday - will see how it goes...
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effkay
post 25th October 2016 08:47
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Did it pass?
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JeremyG
post 30th October 2016 17:53
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Nope - my attempt at a free fix failed.

So, purchased and installed a cheapo cat - and sure enough, it passed with flying colours...
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GialloEvo94
post 30th October 2016 18:26
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QUOTE(JeremyG @ 30th October 2016 17:53) *
Nope - my attempt at a free fix failed.

So, purchased and installed a cheapo cat - and sure enough, it passed with flying colours...

Interesting. Which CAT did you buy?


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JeremyG
post 2nd November 2016 10:04
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This is the cat I purchased:

Cats2U.co.uk
------------------------------------------------------

Products
------------------------------------------------------
1 x ALFA ROMEO 146 1.8 01/97-08/00 Catalytic Converter (BM90389-0020) = 38.39
------------------------------------------------------
Sub-Total: 38.39
Standard Shipping(per item): 8.32
VAT: 9.34
Total: 56.05

VAT No: 948 1576 85

*Cats2u.co.uk is a trading name of G.T.products.

I went for this one because they offered next day delivery, and threw in a fitting kit. There are some cheaper than this...

I'll post the actual emissions figures with the new cat later...

This post has been edited by JeremyG: 2nd November 2016 10:05
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JeremyG
post 2nd November 2016 22:17
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From: Oxford



... and here are the emissions test values:

Fast idle:
CO = 0.56% [should be =< 0.3%] = FAIL
HC = 78ppm [should be =< 200ppm] = PASS
lambda = 1.011 [should be between 0.97 and 1.03] = PASS

Once new cat installed:
CO = 0.06% = PASS
HC = 49ppm = PASS
lambda = 1.001 = PASS

This post has been edited by JeremyG: 2nd November 2016 22:18
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