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(Post Link) post #1 of 23 Old 08-04-19 Thread Starter
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Emissions test failure

Hi, my 156 JTS has just failed the MOT on the emissions test. The garage reckons it probably needs a new cat. It's done 137,000 miles and to my knowledge has never had a cat replacement before. Given the attached test results, would you agree with the garage's recommendation? I'm a bit concerned by the first test failing on some things and the second test failing on the exact opposite set of readings from the first. Why would there be this discrepancy?
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I'm no expert but it does seem a bit strange that the hydrocarbons are high in the 1st test then so low in the second.
Conversely, the items that passed the 1st test are outwith parameters in the 2nd 🤔
Im puzzled.
Maybe someone more knowledgeable will shed some light on this.
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What fuel do you run with?
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Trying to understand emission results to what is happening is often not that straightforward. That said, I'd say you are right to question advice.
As 1st and 2nd tests are opposite, there is no constant. The JTS can be tricky. Best advice is new pre-cat wideband O2 sensors at 100000 miles (as per their design life). Ideally, I'd probably want to see the diagnostic return voltages of the pre-cat sensors- I'd expect about 2 volts at fast idle. If so, sensors may still be ok.

As the CO is generally high and given JTS's tendency to have affected injector spray pattern, I think it more likely that is where the problem is.

JTS cats appear to be robust- even when burning more than a litre of oil every 500 miles.

With a JTS, I'd recommend the expensive fuel (V-Power or Ultimate) all the time but at absolute minimum, the last 2 tankfuls before MOT but running quality super will probably work out cheaper. If emissions is a problem, a concentrated fuel cleaner may help probably ideally added to 1/4 of a tank of fuel and ran as low as one dares. Spirited driving during this time should help. Avoid urban running as much as possible (which is constant advice for a JTS anyway).

If all of the above has been tried, the bad news is injectors out to be ultrasonically cleaned and tested in the hope they come good otherwise go with the fuel injector specialist's advice and get as many new injectors as necessary.
Injector removal is a real pain and will involve engine mountings being disconnected for access (remove inlet manifold).
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(Post Link) post #5 of 23 Old 09-04-19 Thread Starter
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Thanks for the replies.

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What fuel do you run with?
I almost always use normal unleaded from Shell, BP, Esso or Texaco. Very occasionally Tesco (when they have promotions) and very occasionally the expensive variety (e.g. V-Power).

Thanks to Fruity for the advice about the injectors. Sounds like a potentially expensive garage job to remove and clean them. I used an injector cleaner additive one tankful ago (i.e. after using the additive I refilled with normal Esso unleaded and then did the MOT test). I do 50/50 motorway/urban driving, but didn't give it a good run just before taking it for the test. I will connect my laptop to the OBD2 port and check the readings when I get a chance.
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I would stick in a couple if half tanks of the good stuff too and run both down. So, cover a couple of hundred miles and see how it goes
Hope it works out for you without having to resort to the more expensive scenario
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Injector cleaner and a thrashing. Fingers crossed.

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Cataclean is supposed to be good stuff and a number of reviews have said its helped to get cars through the MOT where they have failed on emissions. Been meaning to give it a try...
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Thanks for the further advice. There is, however, the minor inconvenience that I can't legally take it out for a "thrashing" unless it's to a pre-arranged MOT appointment. I suppose I can look for an MOT testing station 100 miles away for that ;-)
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.....and next year take it in 2 weeks early to give you breathing space!
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Yes, I've heard Cataclean can be a miracle cure but a decent injector spray pattern is still needed.

A car can be presented for MOT a calendar month early. If MOT expires on 9.4.19- car passed last MOT on 10.4.18, it can be presented on 10.3.18 and if it passes, the new MOT will expire on 9.4.20.
If the MOT was on 9.3.19, no extra days would be added and it would expire on 8.3.20.

That's how to get a 13 month MOT.
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.....and next year take it in 2 weeks early to give you breathing space!
But if it fails MOT it will still not have an MOT even if the old one has 2 weeks left to run with new regulations.
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Quote:
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.....and next year take it in 2 weeks early to give you breathing space!
But if it fails MOT it will still not have an MOT even if the old one has 2 weeks left to run with new regulations.
Was not aware of this!!
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Yes, they changed it so they get to b**t f*** everyone.

I disagree though. AFAIK, the online MOT check still shows an MOT as valid if it is within a year. I don't really want to get into the contradictory statutory nonsense though. There are still ways around it but I'm just a wide eyed lunatic when it comes to things like that.
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Were the cats actually lit up and hot?

I’ve noticed huge differences on a lot of engines between:

- Driving to the MOT station, having an MOT 15 minutes later

- Driving straight off the street onto a ramp and getting the emissions tested.

Certainly my 155 won’t pass in the first scenario (at all), but sails through the test in the second.
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Quote:
Originally Posted by klint View Post
Thanks for the further advice. There is, however, the minor inconvenience that I can't legally take it out for a "thrashing" unless it's to a pre-arranged MOT appointment. I suppose I can look for an MOT testing station 100 miles away for that ;-)
I know the rules have changed regarding the mot but if the fail is not listed as dangerous then a quick blast shouldn't get you in trouble. I wouldn't like to argue the point with plod or my insurance company mind.

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(Post Link) post #17 of 23 Old 10-04-19 Thread Starter
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Lambda sensor readings

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Originally Posted by Fruity View Post
Trying to understand emission results to what is happening is often not that straightforward. That said, I'd say you are right to question advice.
As 1st and 2nd tests are opposite, there is no constant. The JTS can be tricky. Best advice is new pre-cat wideband O2 sensors at 100000 miles (as per their design life). Ideally, I'd probably want to see the diagnostic return voltages of the pre-cat sensors- I'd expect about 2 volts at fast idle. If so, sensors may still be ok.
I've just measured the two pre-cat lambda sensors. Their status is "open loop" below 1500 rpm and their output is about 2V. Above 1500 rpm their status is "closed loop" and they output about 1.45V. Is that normal, or should they output about 2V at 1500 rpm or above?

I got the same readings with both a cold and hot engine.

By the way, I was quoted £1690 to fit three new cats (the garage said the only way to ensure the cat that needs replacement is replaced, is to replace all three of them!) So I won't be replacing cats as that's twice as much as what the car is worth!

Last edited by klint; 10-04-19 at 22:07.
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I think that is fairly normal.

I can see I should have done a thread on diagnostic data for the JTS just after I overhauled it but I'll try to get some time for comparative data and post this.
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I know the rules have changed regarding the mot but if the fail is not listed as dangerous then a quick blast shouldn't get you in trouble. I wouldn't like to argue the point with plod or my insurance company mind.
Indeed. What you said agrees with The Money Advice Service:

Quote:
You can drive your vehicle with a major fault if your old MOT is still valid, because you took your vehicle in for an MOT early. But your vehicle does have faults that may make it unroadworthy, and if stopped by the police you could be prosecuted.
Which does not make anything any clearer because the second sentence contradicts the first.
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Indeed. What you said agrees with The Money Advice Service:



Which does not make anything any clearer because the second sentence contradicts the first.
It's always been the case that a car that can't pass an MOT isn't roadworthy and therefore legally shouldn't be used on the road even if it has a valid MOT. It's a question of whether or not the police would be able to work out it wasn't roadworthy if you got stopped. Bald tires, broken lights etc are obvious, emissions not ... unless it's belching smoke like a steam train. Even an early booked MOT failure wouldn't be conclusive evidence it was un-roadworthy if you continued to use it before the old MOT expired because you could have fixed it before it expired.
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Quote:
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I've just measured the two pre-cat lambda sensors. Their status is "open loop" below 1500 rpm and their output is about 2V. Above 1500 rpm their status is "closed loop" and they output about 1.45V. Is that normal, or should they output about 2V at 1500 rpm or above?
Mine is around 2.25-2.5 volts at idle.
At fast idle, I record around 1.5 volts.
Mine goes closed loop around 1250rpm.

On the second fast idle test, the lambda was slightly rich (reading below 1.000). The CO reading was consistent. As the first fast idle showed weak, I don't think it is a cat issue but more likely fuel distribution (injector spray pattern) but not so bad as to cause a natural idle fail.

@rxe , pre cats (Euro 3) or later cars which simply have a maniverter reach light up temperature quicker than earlier cars which have a single cat under the floor beneath the gearstick.
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It's a bit contradicting values. Test 1 has high HC and a lambda of higher then 1.3 equaling almost 19/1 AFR. The engine would run very bad if at all at 19/1 AFR . This indicates a misfire. Misfire can only be caused by fuel or ignition problems. I would suggest new spark plugs, a tank or two with injector cleaner and a few hours of high speed driving to clean up the cat and give it another try.

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(Post Link) post #23 of 23 Old 16-04-19 Thread Starter
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It passed!

Not sure how. It could be because I used cataclean and made a large detour via the motorway just to travel to the local garage for the MOT (and then put high-octane fuel and drove for a further mile before going for the test).

Or it could be because the car needed a few other things doing to it (costing a few hundred pounds) and I told the garage I'd only get it done if the car passes the MOT and the garage said they would make it pass.

Thanks to everyone for the advice.
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