Emissions test failure and OBD tools

[JulianUK]

OK, seen a few older posts on this. Just wondering what the latest knowledge is. My UK-based 1997 Legnum VR4 has failed on CO of 0.7% - all other emissions are fine. It was marginal last year, but not this time. I did a good long drive with some cleaning additive as the last journey before the MOT. The car seemed nice and hot for the MOT itself, and the tester tried it several times. Local garages I've tried say they don't have the diagnostic capability to take it on. Not sure what's the next step. I don't mind having a go at changing the cat, but it would be a shame if a) it didn't fix the CO, or b) an underlying problem ends up killing the new cat over time. Air filter is good, plugs and leads oil/filter are relatively new (did them when I changed the lash adjusters last year). What do I need to read the fault codes on this model? Your thoughts most welcome on this - many thanks in advance :-)

[Nick Mann]

It's often just the cat not being quite warm enough. If they are open to the idea, give it a proper Italian tune up on some quiet roads for 10 mins, then screech to a halt by the emissions gear and test straight away. I think the longish downpipes plus water cooled turbos stops the cat getting really hot.

[Confused]

What Nick said is spot on. Even a few minutes idling, even after a "reasonable" drive, and the cat has cooled down too much.

Another trick to "kick-start" the cat if it has dropped out of its efficiency range is by bringing the revs up to ~5k, then snapping the throttle shut a couple of times, then hold it at ~3-4k until the values come down, then go to the fast idle speed for the test.

One year, mine needed to get so hot before the cat would register properly (and it did) that the tester burnt his hand taking the probe out of the exhaust!

[adaxo]

Another trick to "kick-start" the cat if it has dropped out of its efficiency range is by bringing the revs up to ~5k, then snapping the throttle shut a couple of times, then hold it at ~3-4k until the values come down, then go to the fast idle speed for the test.


That exactly what we did to pass through white one (as black one have no issue passing on lpg) revving it's tits off eventually bring figures down. Sometimes if it's on aftermarket big exhaust covering exit helps.

[JulianUK]

Thanks for your replies! I've just tried to read the fault codes by wiring pins 1&4 of the ODB socket, as suggested. When I do that, and turn the ignition on, all of the relevant warning lights start to flash, but there doesn't appear to be any 'long' and 'short' pulses - they just keep flashing at a regular rate. Does this mean anything to anyone? On another thread, it's suggested that MDS Cars in colchester may be able to help - I'm not far from there, so will get in touch.

[Confused]

Regular flashing means no stored errors, so that's good!

Disclaimer - my dad (Allan) works at MDS Cars - so ask for him if you do get in touch with them! ;) He was the one I mentioned who burnt his hand ;) That was before he worked at MDS, when he did MOT testing directly - but he can ensure that the MOT station knows what to do to get the emissions test passed successfully.

[JulianUK]

All booked in at MDS Cars for Tuesday next week. They have the technology :-)

[JulianUK]

OK - all fixed! Allan at MDS Cars in Colchester hooked up his diagnostic kit to reveal no underlying issues, but even after a hard blast, couldn't get the CO down. The diagnosis was therefore a 'tired' cat. One was source from 'Catman' online, and now fitted, emissions are back to where they should be. Now, the fact that the cat was 'tired' was probably helped by earlier lack of maintenance - The car had a very worn out set of plugs when I changed them last year. When hot, it would 'pop' through the turbo(s) when pushing on. Also, your comments above are spot-on regarding getting the cat hot - it's a long way from the engine when compared with most modern cars, so can cool down quite quickly. So much so that the first high-speed run on the emissions test still failed.