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Horrendous MOT emissions results


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My Mk2f failed the MOT today (on emissions), which after all the work I've done on it the last year was a bit deflating to say the least. However the numbers are a bit mental:

 

CO: 12.22%  (Fail 0.3)

HC: 996ppm (Fail 200)

Lambda: 0.669 (Fail 0.97-1.03)

 

My guess from the massive CO readings is a virtually non-existent cat (it looks original to me, certainly very old). Unplugging the lambda sensor on idle does nothing so perhaps that died too?

 

So perhaps I've been used to this rich running for a bit too long and it never was fixed in the first place. In the last year its had new:

Temp sender (OEM), Plug, Leads, Dizzy cap and rotor, all filters, multiple oil changes, Thermostat, head gasket, water pump, timing belt, ignition timing set to 5 degrees BTDC. Gave it a proper thrash this morning before the test.

 

Last week I changed the centre silencer as the old one took a thump in France and developed a hole. Looking inside the old one there is something in there.... could it be some catalytic monolith perhaps? Only a year ago it passed emissions with flying colours - nothing I've changed should have made anything worse and with these SPI engines there isn't anything left that controls the fuelling aside from the cat and lambda right?

 

 

 

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good stuff    some folk add an extra to the o2 sender for good measure too 

Had a bit of time today so finished off installing the new cat and joining it up with the rest of the exhaust. As per their instructions I 'ran it in' on idle for 10 minutes and then went for a normal

athe broken earth made the car think it was freezing outside , car ran overly rich and ruined the o2 sensor and cat by running so rich   the blue temp sender and its wiring are key to these

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14 minutes ago, kiran_182 said:

Early hg failure can cause this 

 

Anything I can check to confirm this? I replaced the head gasket at the beginning of the year and its done around 9k miles on it since. Not willing to take the head off yet again unless its totally necessary.

 

All of the plugs are the same (tan after a hard run, sooty otherwise as per this rich running), no steam cleaned plug. No mayo in the oil, no visible gas bubbles in the coolant header tank. Doesn't use oil or coolant either.

Edited by zob
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steveo3002

the cat might not be any good but isnt just that to blame

 

one of these with no cat should still show under 1% co 

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22 minutes ago, zob said:

Doesn't use oil or coolant either.

On inspection this doesn't appear to be the case actually - used half the dipstick indent since I last checked a month or so ago.

 

Damnit. Could this be from the overheating we experienced in France this summer? Coolant bubbled over when stopped a few times, never overheated when underway though. If its burning oil its not burning heaps of it - would it not take much to produce such high HC and CO readings?

 

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5 minutes ago, zob said:

 Coolant bubbled over when stopped a few times, never overheated when underway though

And just for those that didn't see that particular thread - it was just down to a broken expansion cap seal not keeping system pressure

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37 minutes ago, steveo3002 said:

the cat might not be any good but isnt just that to blame

 

one of these with no cat should still show under 1% co 

 

No cat + duff lambda could bump up the numbers perhaps?

 

4 minutes ago, kiran_182 said:

High hydrocarbons is an indicator of early hg trouble, overflowing expansion too

Also an indicator of v rich running though too right? The expansion only overflowed because it was un-pressurised and the coolant boiled in the head when the engine was turned off after a hot autoroute run. Although I agree that the consequence of which could be a failed HG.

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steveo3002

disconnected o2 and no cat should be not far off the pass figures , its only there to fine tune it 

 

12% is mental ...surprised its running , imagine it would stink of fuel and blacken the plugs

 

dont really know what to say or suggest ..guessing theres no indication of misfire?  , id nt fit a new cat or o2 sensor until its sussed out , as id imagine running that rich would ruin them quickly   

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9 minutes ago, steveo3002 said:

guessing theres no indication of misfire?  , id nt fit a new cat or o2 sensor until its sussed out , as id imagine running that rich would ruin them quickly   

 

No misfire but it chug-chug-chugs when cold (until ~75degrees). Definitely not a misfire - unplugged leads one at a time got a proper miss each time. Smells a bit once warmed up but nothing crazy (not like when its cold, bloody stinks then). It runs at 40mpg average, nothing that far out of the ordinary.

 

Could it be the tester just didn't test it at operating temperature like he said he did?

 

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steveo3002

check the blue temp sender readings at the sensor ...and check the reading is getting all the way to the ecu

if its faulty the engine will think its cold

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steveo3002

as for the mot tester , id not be surprised , i wait there and watch them like a hawk 

 

any older car its worth taking on a long blast to reach full temps and straight into the test center hot , im no expert but those figures look too high for a cold engine 

 

 

 

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26 minutes ago, steveo3002 said:

check the blue temp sender readings at the sensor ...and check the reading is getting all the way to the ecu

if its faulty the engine will think its cold

The sensor reads sensible resistances and reaches a negligible resistance when warm - I'll check the look tomorrow in case an electrical gremlin has made its way in somewhere.

 

29 minutes ago, steveo3002 said:

as for the mot tester , id not be surprised , i wait there and watch them like a hawk 

 

any older car its worth taking on a long blast to reach full temps and straight into the test center hot , im no expert but those figures look too high for a cold engine 

 

 

 

I drove it from Oxford to Birmingham and straight into the centre this morning (properly but they couldn't guarantee a test time for the day so I had to leave it with them. However when I picked it up and drove it away the temp gauge popped up to ~75 so it must have been at least that warm when tested earlier.

 

I'm going to go round and quizz them about the numbers tomorrow because something doesn't add up here. Even if it was burning a little oil (and it must be burning very little indeed unless its secretly getting oil from someone else) would the CO be that astronomically high? I mean could it be something as simple as a decimal point out of place on the CO?

 

 

 

 

 

 

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steveo3002

had to say , id be tempted to find an old skool garage thats intrested in helping , most garages will have a gas tester they can put on it and see whats going on

 

hard to believe its done 9k and getting good mpg if its that far out 

 

does your have the diagnostic plug near the glove box area  never had a spi myself

 

from memory you need around 350-450 ohms on the blue sender when hot , around 2000 cold , check at the sensor and trace the wires to the ecu and conform the ecu is seeing the true value incase of a squashed wire  

Edited by steveo3002
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lambda 0.669 (*14.7) is AFR 9.8:1 (for petrol) which is plug fouling rich and sooty smoke out of exhaust.

High HC is unburnt fuel or oil.

 

Check the plugs? 

Oily or sooty or clean will guide you. If oily and ignition timing right, compression or preferably leak down test will confirm the worst.

 

 

 

 

 

 

.

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Thanks guys - I'll have a thorough look again tomorrow, good thing I can work from home...

 

Last I checked the plugs (about 200 miles ago) They were sooty apart from the insulator and cathode/anode which were tan after a motorway run.

 

One thing I did do since it passed its emissions last year (and owner), apart from replace with new OEM parts, was to advance the timing. The tick on the aux pulley, according to Haynes, needed to be at the other end (I.e. counter-clockwise end) of the 'window' for 5 degrees BTDC. My question - how much could too much advance affect the emission readings? The last owner scratched a line across the dizzy so I could always put it back if needs be. Its not pinging so I thought it would be fine (if not beneficial?) to have a bit more advance. Can't be more than 1 or 2 degrees off at most

 

 

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steveo3002

couple of degrees out on the timing wouldnt do it , pretty common to run a little more advance

 

dont take it as gospel..my thoughts are ....blue sender or wiring - car thinks its freezing cold when its not  , ecu problem , or problem with the spi unit 

 

if its really been running so rich chances are its damaged the o2 sender and cat too

 

is the oil level correct...smell it might be contaminated with fuel , consider changing it after its repaired 

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Right... might be getting somewhere (having to dart in and out of the house with this bloody rain at the moment!)

 

All of the plugs are sooted (not surprising), with some white deposits between the electrodes that I assume is oxides. No difference at all between plugs - they're all uniformly dry carbon fouled.

 

Temperature sender reads just shy of 3k which is correct for today's cold equilibrium temperature (probably around 17 degrees today eh). There is continuity between the green/grey signal wire on the sender plug and pin 10 of the ECU plug (or what I assume is pin 10 - there's continuity with a pin anyway). However, the brown/white wire that is supposed to pair with pin 8 and earth is not showing continuity with any of the plug pins and shows infinite resistance to all engine earths and the negative battery terminal. Double-checked against other sensor earths and all of the others show continuity with ground - looks like the sensor doesn't have a ground. With nothing to measure resistance across I assume the ecu is seeing freezing temperatures all the time.

 

Going to keep darting out inbetween showers and start peeling back the looming tape to get to where this wire is going. Is there a pin diagram for the ECU plug anywhere online? I have the electrical diagram in Haynes but there aren't any numbered markings on the plug to cross-check.

 

Pretty narked - I was sure I found this earthing fault before and fixed it, evidently I didn't.

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steveo3002

easiest fix if get your self a length of wire and some crimps ....replace the earth wire at the blue sender plug and then either follow the loom up and join it near the ecu(dont cut the wire as other sensors share it , or simply fit a ring terminal and earth it on the head or other convenient location ( id go for a earth on the head etc)

 

should be pin 8 at the ecu shared with brown white on throttle pot and inlet temp

 

if this appears to fix it id suggest a oil change and a good motorway run to see if will clean up the cat /02 sensor

 

https://www.ebay.co.uk/itm/10-x-Junior-Timer-Contacts-Genuine-TE-Part-Part-No-925596-1/140938481505?hash=item20d0968f61:g:bdIAAOSwvlJZ5NDs

 

https://www.ebay.co.uk/itm/RANGE-OF-FULLY-INSULATED-CRIMP-RINGS-Electrical-Wire-Terminal-Connectors-Cable/192097004531?hash=item2cb9dfabf3:m:mpFiDZXJMN5wK1_vEGvi0nA

Edited by steveo3002
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steveo3002

https://www.ebay.co.uk/itm/LASER-3932-Terminal-Tool-VAG-VOLKSWAGEN-AUDI/273294488055?hash=item3fa19ef1f7:g:Da8AAOSw6VNbIh-V

 

these are to release the terminal, can get away with a thin screwdriver or such for a one off job...have a look at the other links and see the 2 prongs you need to push down

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Followed  the earth wire from the sender and it goes to the large multipin plug on the loom/conduit that sits ontop of the inlet manifold - 23 on 7zap:

https://volkswagen.7zap.com/en/rdw/polo+derby+vento-ind/po/1993-120/9/971-123000/#23

And it has continuity through to there - i assume thats the shared earth connection for the other sensors. Dear god, have I been running without a ground for those too?! Surely not!

 

I've got a load of wire and some ring terminals so i'll make use of those.

 

Trick is finding which is pin 8 on the ECU plug - not very obvious...

 

Thanks for the help chief.

 

 

 

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steveo3002

heres what i have...dont trust it 100%  you should be able to see what wire colour goes in the reverse to confirm

 

 

image.png.83c7d13ff0eac88fcf7f668e8652a8b3.png

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Right. Can't explain how but after removing and replacing the battery neg connector, ECU plug and the loom tape there is a perfect connection from the sender plug to pins 8 and 10 and the plug is seeing the same resistance as the sensor (which is correct). Put in cleaner (but not new) plugs and it started as normal - but crucially the engine didn't 'chugchugchug' through the warmup phase and there is nothing but steam coming out of the exhaust. Smells fine too.

 

I'll give it an oil change now and maybe run a bottle of cataclean through it, see how it goes.

 

Either a pin in the ECU plug wasn't making a good connection or it somehow locked the sensor out (I thought the monotronic was too stupid for 'limp home' modes etc?). Either way the earth wire visibly travels its length with no crimps or shorts - nothing wrong there.

 

Bloody electrical gremlins. Honestly I thought I'd given them up along with my old Volvo 240...!

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steveo3002

or wiggled a broken wire in the loom?

 

if the ecu doesnt see a signal it defaults to -40 so way too rich 

 

sounds like youre onto something ...id guess the wire is broken /weak somewhere 

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26 minutes ago, steveo3002 said:

or wiggled a broken wire in the loom?

 

if the ecu doesnt see a signal it defaults to -40 so way too rich 

 

sounds like youre onto something ...id guess the wire is broken /weak somewhere 

 

Aye, I'll replace the wire properly rather than jury rig on a new earth, for now I'll just make sure it does its job to get through the MOT.

 

The idle isn't particularly steady when warm now - I wouldn't be surprised if the lambda sensor is coked right up or on its way out. Got another one coming in the post which I'll pop on the new cat and install both of them if the next emission test is a pass (or a much closer fail).

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