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MoT test instruments: how accurate are they?

Discussion in 'General Cars' started by Alec_t, 19 Sep 2020.

  1. Harry Bloomfield

    Harry Bloomfield

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    Isn't the process one of the water turning to steam in the combustion chamber, to release extra energy, thus turning the engine into a sort of steam engine? The water would have to be off until the engine was hot and turned off before arriving at the destination, plus the EGR disabled if the water was injected at the inlet.
     
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  3. Tigercubrider

    Tigercubrider

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    My Volvo has a Mitsubishi GDI engine and I do short journeys- it would be better used on long ones.
    I have had two major issues with injectors/ intake as it gungs up. In an ideal world I wouldn't have bought it (never heard of the issue at the time) so I try to go for a thrash just to clear it- but it's a pita
     
  4. Harry Bloomfield

    Harry Bloomfield

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    A diesel engine is much more of a problem used on short runs - diesels, because they are so efficient, take a very long time to get to up to operating temperature. I'm looking at 10 to 15 miles before mine gets to temperature in winter, much longer if any attempt is made to use the cabin heater. It is so efficient, they added a diesel burning boiler system, to help speed it up on colder mornings (night heater style).
     
  5. Avocet

    Avocet

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    OK, it was really the methanol that I was raising an eyebrow over though.
     
  6. Avocet

    Avocet

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    I don't see it as inevitable though. Before this Freelander, Mrs Avocet had an X-Trail. I saw so many scary photos on the owners' forum of inlet manifolds that you could barely shove a pencil down, because they were so choked with crap that when hers hit 100,000 miles, I thought I'd best take it off to have a look. What I found, was... absolutely nothing! A light coating of oily soot round the walls of the manifold, but by "light" I mean something that could come off with a rag, rather than be scraped off. The car (in the 60,000 miles that we'd had it) had never done a run under 5 miles, and would get an "Italian tune-up" once a month or so. This Freelander (which was always very gently-driven) and now that I have cleaned it out, it is showing no signs of building up new accumulations, even at 155,000 miles, under the same regime.

    I'm also not convinced that very much comes past the turbo seals (unless they're knackered, obviously)! I think the vast majority is crankcase fumes, but have no way of proving that.

    I'm fundamentally against blanking-off EGRs (or disabling any other emissions control device), to be honest. It's not that I'm some raving tree-hugger (I wouldn't have a 2001 diesel 4x4 if I was!) but I do, at least feel somewhat self-conscious about it and try to keep the miles down, and keep all the emissions control devices as OE. As a 2001 diesel, the only MOT check is for smoke. There's no Co or HC check, so I could bin the cat, if I wanted. As you say, they can't even check for NOx. However, the practice is widespread. Pretty much every car mechanics forum you go on, there are threads about deleting EGRs (and other things). The trouble is, we're "peeing in our own swimming pool", for want of a better expression! Our air quality in cities and near big roads, is pants. The authorities are responding by bringing in low emissions zones and, more recently, reducing motorway speed limits on certain sections where air quality is bad. IF we (consumers in general) keep disabling these devices, we're only going to end up with more of the same measures...
     
  7. Mottie

    Mottie

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    All diesel checks on any year vehicle after 1980 is for smoke only.
     
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  8. Harry Bloomfield

    Harry Bloomfield

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    That would have me wondering if it had been already defeated. Mine was well caked, EGR, manifold and inlet at 90K miles, but probably not enough to seriously affect performance. My concern is that the authorities/manufacturers are just swapping NoX pollution early in the life of a vehicle, for much worse carbon soot pollution after the vehicle has done a few miles. We have all seen clouds of soot coming from the exhaust of well used diesels.

    There are several ways to defeat the EGR - blocking the exhaust connection, blocking the vacuum pipe, defeating the control wire connection, or replacing the EGR body with a dummy version.
     
  9. Keithmac

    Keithmac

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    There's oodles of research papers from World War 2 era about water injection into aeroplane engines, really interesting reading.

    Used to be common in rally cars too until they banned it. Aquamist in the UK is leading manufacturer of water injection systems for cars.

    The Harrier Jump Jet uses it when doing vertical takeoffs and landings, has approx 5 mins worth of water reserves iirc.
     
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  11. Avocet

    Avocet

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    Gosh! Really?! Even for diesel cars that have just turned 3 years old?
     
  12. Mottie

    Mottie

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    Yep. Its near on impossible to get ANY readings from DPF equipped cars. Used to have to abort the smoke test and write on the emission copy that we had to keep for 90 days "Unable to obtain smoke reading". Run your finger around the inside of the tailpipe of a modern diesel and you'll see no soot at all on most occasions.
     
  13. Avocet

    Avocet

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    No, the EGR valve worked fine, I had that apart at the same time and it was all "doing its thing". As I mentioned, I wouldn't want to disable it. Besides, it's harder to delete them on a "Euro 4" X-Trail anyway, because you get engine management lights and limp mode. There are, of course, ways round it....

    I'm not sure about "swapping" NOx for soot. It's a bit like swapping a kick in the nuts for a poke in the eye - they're different things, neither of them pleasant. We seem to be getting on top of particulates much better than we're getting on top of NOx just now. The particulate filters will stop (if they are working correctly and haven't been tampered with!) the clouds of soot coming from well-used diesels. Sure, they can't work miracles, and by the time the vehicle gets to be "well-used" it is bound to be smoking more than when it was new, but this extra should still be caught by the DPF. It'll just have to regenerate a bit more often than when the car was new. In fact, new diesels are now generally BETTER on particulates than new petrol vehicles (which is why we're starting to see the emergence of "GPFs" - Gasoline Particulate Filters). Hopefully, the recent AdBlue innovations will reduce the NOx to the point where EGR won't be necessary.
     
  14. Avocet

    Avocet

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    Yes, that has been my experience of them. The MOT smoke meter is a pretty "cheap and cheerful" tool for checking, but there would be something wrong with a DPF-equipped car if you got any kind of meaningful reading on an MOT smoke meter. In the type approval emissions test, they're down to counting individual numbers of soot particles these days! However, I'd have thought that they'd at least have CO and HC requirements to meet?
     
  15. Mottie

    Mottie

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    Definitely not on diesels. Only on Petrol. Two different machines are used. If you tried to use the emission tester on a diesel and give it a good rev, you'll clog the machine up with soot and will have to change the filters and clean the pipes out. Don't ask me how I know that...….:whistle:
     
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  16. Avocet

    Avocet

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    I don't think so. My understanding is that the benefit comes from it cooling the incoming charge and making it more dense so you get more air and fuel mixture into the cylinder. You need a colossal amount of energy to split the hydrogen and oxygen atoms in water apart from each other (which is why it's good for putting fires out), so I don't think any extra energy comes from the water itself "burning" as such.
     
  17. Avocet

    Avocet

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    OK, that makes sense, thanks. However, I'd have thought (for the reasons mentioned above) that it would be OK on DPF-equipped diesels?
     
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