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Mot Emissions Failure


grum76
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I don't mind admitting that I'm a real noob when it comes to cars. I can do petrol, oil, water, etc but thats as far as it goes. I recently had a whole new exhaust fitted from top to bottom and put the car through it's mot the following day at the same garage. It failed miserably on the emissions, and even when I took it back to see if they could fix it they said it was still too high and that it was probably a result of a tired, old, engine. Effectively saying that I should scrap it. They also claimed to have put some fuel treatement in the car, but not having been able to give it a good run to push the stuff through the system said it was hard to say if the stuff had been pushed through and that I should perhaps take it back in a couple of days just to see. So my question is, if it's not the exhaust cuaing the problem (and the airflow thing, they say, would not be enough to give such high readings) would you guys hazard a guess?

I dont really want to scrap my car, but I also realise that there is only a certain amount you can spend on a car before it seems like your throwing it down the drain.

I dont know if it helps any, but none of the sensors were replaced during the new exhaust fitting. As I have been told, there is a sensor before the cat.

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There are two sensors before and after the cat.

Both are lambda sensors and are used to balance the fuel/air mix in the engine.

If either is misreading then the engine will run too rich which is probably what's causing your problems.

I'd hazard a guess that you're failing on excessive CO and Hydrocarbon levels.

Fuel additives will only go so far but are unlikely to improve emissions, they're more tailored towards economy and the fuel inlet systems (injectors etc).

I strongly recommend you look at a procedure called Terraclean, i had it done to my diesel Focus a short while back and the car runs like new, fuel economy is now excellent and no smoke even on start up.

On a petrol engine it will cosy about £100, take approximately an hour and will cut your emissions drastically.

Search the web for Terraclean, check local availability and go for it.

I strongly recommend it (this is not a forum or formal endorsement just my personal suggestion due to experiences).

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do you have a copy of the emissions test?

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Sorry, I did mean to put the readings up. So I'll pop 'em in here. And being as it was only the CO that was at fault, I'll just add their readings as all the others were ok.

As for both sensors, I was told there was no way that they would make the readings so high. And in looking at the test sheet both lambda sensors passed.

Fast-idle test:
CO max 0.30% --- 0.53%

Second-idle test:

CO max 0.30% --- 0.53%

Natural Idle test:

CO max 0.50% --- 0.62%

As I said everything else passed ok, and the whole thing is confusing me somewhat.

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any idea on HC readouts

lambda sensors can make emisions that high, we're only talking 0.2% to bring it into line,

i would change the oil/filter using a good quality 5w/30, more often than not that will be enough to drop the readings and not wasting your money unless its been done recently.

failing that, a general engine service would help, plus check the ecu for codes/live data for readings such as temp sensor...

lambda readouts are not actually testing the sensors, so cannot rule out sensors on that basis

live data or lambda sensor testers are only way of testing sensors themselves

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HC readouts were :

1st: 74ppm

2nd: 54ppm

Seemed odd the garage was eager for me to scrap it though. I'm doing as they asked though, and running it hard for a day or two and then allowing them to put it back on the machine to test the emissions again. But failing that I know a garage that have said they'd look at the ecu codes. I'm not even sure of the garage did this when it went in to be looked at for repairs, they never said. As much as I know they said it's a dead engine, but it fires first time and runs as sweet as a nut. Maybe I;m being too hopeful?

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Tbh if the garage is suggesting you scrap your car they're overstepping the mark.

The job of an MOT tester is to say pass or fail and not to make recommendations.

I think they're too keen to drum up work rather than do as they're supposed to do under MOT regulations.

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i definitly wouldnt write an engine off on those figures, it just a mere 0.2%, ive seen and cured far worse on far later models...really dont get that thought????

if hc is under 100ppm its telling you that is burning vast majority of fuel being thrown into the cyls....could also be a sign of a sluggish lambda sensor especially if lambda readout is on the lower end of the scale....[HC measure unburnt fuel comin out the tailpipe]

going on your first post, are the readings you give lower than original test readings or are they the same?

trust me, those figures are a minor problem, but could be a pain to trace the fault as there is so many possibles...

start off with fresh oil/filter, check condition of air filter, change the plugs, especially if they dont have the platinums fitted..

would do the above followed by a decent drive before any fault codes/data checks , as any of those could throw a problem and confuse the sensors.

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The reading's I gave are the ones from the first test. They said they had done the test again today but never gave me a sheet. It had new plugs and a coil pack about 3 months ago. Someone else has suggested a new air flow sensor. But between now and going back to the garage I'll have done roughtly 70 miles or so, Not a vast distance, but with no mot on it at presant I'm loathed to go much further out than that.

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this is where diagnostics come in....dont be tempted to have a new air flow fitted on a whim...all sensors can be tested without the need of hit and hope, by proper diagnostics.

couple more questions

did new exhaust system include a new catalytic?

were the lambda sensors removed in exhaust change?

mondeo was known for burning oil, does yours?

if mot garage is willing to test gasses free, i stand by changing the oil etc, but also get the engine fully warmed up before retesting..a cool engine could easily give the figures you have. the oxygen sensors/cat need to be up to temp before they work properly...that is why the sensors are electricly heated as it takes time for the exhaust temp to raise the sensor temp up high enough for them to work 100%

also, if possible, get the codes [if any] read and dont jump to any conclusions that those codes are telling you exactly whats wrong...they are only a clue and everything should be tested before paying out for replacements

for an eg of what can cause a minor excess in CO....oil. coolant temp sensor, lambda sensor/s, catalytic, injectors, map sensor, engine breather, air filter, air/vacuum leaks/blockages, wiring, ecu, throttle sensor etc, etc....so dont be talked into taking a chance as it could end up very expensive for what is more than likely a minor problem...

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Regarding the lambda sensors, do you mean removed and not refitted? I have no way of telling this if that's the case. In any case, when the new exhaust was fitted nobody made mention of new sensors or that ones had been replaced.

And the new exhuast came with a new cat. I'll look at the air filter again. I do remember tapping it out to clean (not replacing it with a new one) so maybe if I'd not shut the air filter casing properly and left an opening, do you think this would affect it? Either way I will look soon and let you know what I find.

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Curiously though, regarding the emissions figures, you guys don't seem to phased by them when the garage said they were monsterous.

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try some forte i have used in the past just before an mot with surprising results on a diesel and petrol its not cheap about £18 a can and you put the whole lot in its the only one i have found that works

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figures you have given us are not monstrous, ive seen figures of way over 5% and beyond, so long as figures you have given are correct, then they are only approx 0.2% out

i have done many cars, not just Fords, with very similar readouts and more often than not cured them with a simple oil change using good quality and correct grade oil.

with a new cat fitted then chances are lambda sensors were removed, these are extremely delicate sensors and could have been damaged on removal/refitting...would recommend having them tested

which begs the question why was cat changed in first place?

a badly fitted air filter box lid is unlikely to cause emmission problems, sounds like air filter itself is unlikely to be the problem as if it looks clean then just shake out any dust etc and refit properly

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The whole system had to be changed becuase there were cracks in the pipe they said had to be fixed. One on the down pipe from the engine, one after the cat, and the larger leading into the middle box. I was told the pipe was too old to be split and only the affected parts changed. So I paid £225 for a whole new system. Not sure what make it is though. As for the lambda sensors, the report says they all passed the test. It's just the C02 that's the problem. oil was put in not long ago as it was low on the stick. Correct oil according to the garage.

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lambda readout on mot sheet is not testing the lambda sensors. they are, in most circumstances, totally unrelated.

lambda sensors regulate air/ fuel mixtures by measuring oxygen that passes them in exhaust system...

so a working sensor may increase fuel as its detecting excess oxygen, resulting in CO being high, but lambda readout on tailpipe is peferctly within limits

alternativly, a non working sensor can be compensated by ECU or others sensors, resulting in high CO but perfect reading at tailpipe..

hope that makes sense

adding new oil to old will not make any difference as new oil is immediately contaminated by the old, it needs draining and refilling with quality 5w/30 oil..im not saying this will cure your problem, but its a very important issue when it comes to minor CO failures...changing oil does the engine a world of good and a strong chance of making all the difference in the readouts, saving you money in what could be a time consuming diagnostic check....when i get customers with similar issues, i wouldnt even plug a machine in untill that oil/filter are changed and gasses rechecked

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