Xantia failed smoke test

[lazza]

HI

Just had my spanish MOT done. All was fine, but it failed its smoke test. Instead of 2m-1 of opacity it had 11.71m-1 of opacity (whatever that means)

I had been noticing black puffs of smoke from the exhaust the last year with rapid acceleration. It seemed particularly bad today so I wasnt surprised when it failed.

Could the forum give me some pointers on how to mitigate this without having to take it to a garage?

Cheers
Larry

[Hell Razor5543]

I would check the air filter first. If it is clogged you can get poor combustion. Something else you might want to try is to take the car for a nice long high speed drive. This can help to clear things out.

[Peter.N.]

Yes, I always give mine a good thrashing on the way to the MOT because if its only been driven gently it can accumulate a lot of soot in the exhaust and this is what it will blow out on test.

Peter

[Stickyfinger]

When did it last have a good service, eg, tested on a Lexia, fault codes read/checked, injectors checked, fuel filter, AirFilter...etc ?

[chinkostu]

Al, a 96 TD (like mine) won't show much on a lexia bar ABS really as they're pretty much all mechanical, no ECU so no check engine light just a crank sensor for the tacho and sensors to kick the fans in. Might be able to read temps and revs but that all depends on if the dash outputs it to the socket aswell!

as said, check filters. They're cheap and easy to replace. Also check you've not got any boost leaks as you'll get smoke from incomplete burn if theres a leak

[superloopy]

Mine chucks out white smoke on startup ... ?

[isisalar]

Removing the air filter completely for the re test will probably do the trick.

[lazza]

What's a boost leak?

[electronmirror]

When the turbo is blowing it produces a boost to the air supply into the inlet manifold. If you have any holes in the large diameter rubber pipe feeding the inlet manifold you will get 'boost leak'. The fuel pump won't know that and will deliver more fuel than can be burned completely hence incomplete combustion and black smoke.

Check that big pipe from the turbo outlet all the way to the inlet manifold.

Good luck

[BX]

1 litre of Dipetane in the tank and a good hard drive to the test will sort it. Not sure of sterling prices but normally costs 12 to 15euro.
Edit: just noticed you are in Spain so euro prices.

[chinkostu]

Mine chucks out white smoke on startup ... ?

Glowplugs working? Does it smell of diesel?

[MikeT]

Mine smokes like a destroyer trying to hide itself and passes the emissions tests every year so yours must be really bad (or the tester chose the incorrect limits for your car) to fail by over 5x the limit? Are you sure it's black smoke and not blue?

I just noticed, you run veg oil - it should burn even cleaner.

I always present my car for it's MOT with new oil and filters and, as others mentioned a good thrashing (or italian tune-up) to blow out the accumulated soot from the exhaust. If it still fails, you may need injectors cleaned/replaced or something more sinister is going on. You can de-tune the pump for less smoke (and therefore less power) but that would be a last resort imo.

The fuel pump enrichment relies on boost pressure so I can't see how a boost leak would cause overfuelling - happy to be shown wrong though.

[chinkostu]

Mine smokes like a destroyer trying to hide itself and passes the emissions tests every year so yours must be really bad (or the tester chose the incorrect limits for your car) to fail by over 5x the limit? Are you sure it's black smoke and not blue?

I just noticed, you run veg oil - it should burn even cleaner.

I always present my car for it's MOT with new oil and filters and, as others mentioned a good thrashing (or italian tune-up) to blow out the accumulated soot from the exhaust. If it still fails, you may need injectors cleaned/replaced or something more sinister is going on. You can de-tune the pump for less smoke (and therefore less power) but that would be a last resort imo.

The fuel pump enrichment relies on boost pressure so I can't see how a boost leak would cause overfuelling - happy to be shown wrong though.

When i bought mine the pipe from the intercooler was off and the missus commented on the smoke!

[lazza]

Yeah, i normally run on veggie oil and it smokes less, but for the test i fill up on normal diesel so they dont get funny. But it's definitely black smoke. Glow plugs are new and no it doesnt smell of diesel. It only happens when you really kick down on the pedal

So what from what you tell me, it could be:

1. A boost leak, I will check the turbo piping
2. Air filter, but i doubt it as it was changed not long ago
3. Injectors

AS I've never had problems on the emissions before I didnt know about giving it a thrashing beforehand. However, I'd like to find out it there is some underlying problem, cos I dont want to go back and it fails again- then I'll have to pay for another MOT and so it will go on.

I have also played around with the pump alot recently- could it be that it is injecting too much fuel??

[MikeT]

I have also played around with the pump alot recently- could it be that it is injecting too much fuel??

Depends what you played with exactly but Yep! Definitely could be.

Don't worry about thrashing these diesels. Firstly, they're diesel and built stronger than petrol engines. Secondly, the fuel pumps are so heavily governed, you're not really thrashing them at all. They could produce so much more power without worry but the resultant smoke (search youtube tractor-pulling) would make you the most hated motorist wherever you go.