A chum has just had his 2005 Passat 1.9 TDI fail its MOT on the new (2018) emissions standards.

The car had always passed prior to the standards being tightened last year and has been properly serviced, etc so this was a shock to him. He has had a variety of suggestions to rectify the problem such as additives, running the car at high revs for a good distance, etc.. He fears he may have to replace the car.

It is fair to say that his driving style is very relaxed which may be part of the problem - the car never sees high revs. I think it has done about 110k miles.

 

There are a lot of knowledgeable and helpful folk on here so I'm hoping someone may have had a similar experience and be able to offer advice which will be much appreciated.

 

(I did try a search for this issue without succes but, if it has been covered elsewhere, please advise the thread. Thanks)

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What is the actual fail on a 2005 Euro 4 emissions diesel.  Visible Smoke?

Might be worth your chum looking for the 'manufacturers plate' as described in here, and seeing what, if any, smoke value is on it.  https://www.gov.uk/government/publications/mot-changes-from-may-2018-guidance-for-mot-testers/diesel-vehicle-emission-limits#new-default-limit-for-newer-vehicles

 

A literal reading of the rules suggests that if that plate with its smoke value was 'unable to be found', the more relaxed default limits should be used - 3.0/m for a pre-2008 turbo.

 

 

What did it fail on? Visible smoke or smoke reading higher than limit?

 

What was the fail code number?

According to the list in section 8.2.2.2 here, it shouldn't fail on visible smoke unless it has a DPF (fail code 8.2.2.2d), but the document I linked to above doesn't mention that; so an internal contradiction.

Does the car have a DPF?

Edited 5 February, 20197 yr by Wino

Thanks for the quick replies.

Apparently it failed by exceeding the "Plate value" which is on a sticker on the car. It doesn't have a DPF - too old.

I'm afraid I don't have any more details. The MOT examiner commented that they are seeing quite a few such failures.

It would be interesting to know what the plate value is, and how much it exceeded it by.

The standard advice would probably be to book a retest at some time when it can be preceded by a brisk higher-than-usual rpm drive of something like an hour's duration.

Although smoky diesels aren't exactly to be encouraged, building new cars to replace them has huge environmental costs which are rarely considered in this 'consumerist' world we live in; so I'd say trying to get it through is worthwhile.

A well maintained car shouldn't fail on smoke emissions. My '99 B5 Passat had a fairly smoky tune and it always tested well inside the 1.5 /m limit, never mind the 3.0 /m limit it was subject to.

 

Best solution for this car is probably run something like LiquiMoly Diesel Purge through it and give it an Italian tuneup. If the owner is uncomfortable doing the Italian tuneup, he could lend it to someone who has no qualms doing it. I'd wager there's a bunch of soot lying around inside the turbo and exhaust that's getting dislodged during the test.

My parents' old VW Sharan 1.9 TDI needed an "Italian tune up" come MOT time. Partly due to dad's driving style (captain slow) and probably also due it being from the pre-DPF era.

 

Retests are usually free, so I would try giving it some full throttle acceleration and driving for a while at higher revs. If that doesn't work then consider running some premium diesel (V-Power or similar) through it, or using a fuel additive.

I will pass on the recommendations for the "Italian tune-up" - thanks.

He has had conflicting advice on using an additive. His garage recommended it but a mechanic friend warned that it might loosedn up even more muck although I guess a good long blast should blow that out.

That's a good point about re-tests being free. He could try giving it a good thrashing on his way to a retest and see what happens.

Thanks for the help.

I've used this  https://www.ebay.co.uk/itm/Millers-Oils-Diesel-Power-Ecomax-Fuel-Additive-Treatment-500ml-0-5L-NEW-IMPROVED/182909145476?epid=527790580&hash=item2a963c1184:g:5CcAAOSwYwZcUWPf:rk:2:pf:0

on previous older diesels I've had.  I poured the full contents of the bottle into a full tank of diesel, ran it for about a week before the mot and on the day of the mot gave it a good warm up and never had a failure.

Ikinda fell down a rabbit hole this morning along the engine cleaning tunnel. (Not terracleaning etc, just diy stuff)

I do reckon the inshi7nia needs a clearing out, egr, throttle body etc.. so, leading off the above, anybody used the "into the air intake spray stuff" for decrapping? Any difference to the in fuel? Obviously removal and scrubbing is the best option, but i cba

 

On 05/02/2019 at 19:39, silverden said:

I've used this  https://www.ebay.co.uk/itm/Millers-Oils-Diesel-Power-Ecomax-Fuel-Additive-Treatment-500ml-0-5L-NEW-IMPROVED/182909145476?epid=527790580&hash=item2a963c1184:g:5CcAAOSwYwZcUWPf:rk:2:pf:0

on previous older diesels I've had.  I poured the full contents of the bottle into a full tank of diesel, ran it for about a week before the mot and on the day of the mot gave it a good warm up and never had a failure.

 

I can second using miller's, used it in my old Mégane and it was still going lovely at 230,000 miles. I followed the instructions and used it most times I filled up. Go for a 3rd gear blast to clear out soot, a few short blasts should do it, and you should see the improvement in the rear view mirror!

 

Thanks for those recommendations: I have passed them on.

If you live near NE Hampshire watch out for an old Passat thundering along at high revs in a low gear and trailing a smokescreen!

19 hours ago, mac11irl said:

I do reckon the inshi7nia needs a clearing out, egr, throttle body etc.. so, leading off the above, anybody used the "into the air intake spray stuff" for decrapping? Any difference to the in fuel?

Assuming the arrangement of bits is similar to what I'm familiar with, the stuff that goes in the fuel tank has no hope of doing anything about deposits in the TB/EGR/inlet manifold cos it will be injected downstream of all of those.  I find it stretches my credibility to imagine enough active ingredients will be left after combustion to recirculate round the EGR system and clean stuff 'on a second lap' as it were.

Spraying stuff in the intake seems more likely to do something to those parts, but somehow my gut tells me that an old toothbrush and a bit of carb cleaner will do 100 times more per pound spent.

 

But then those deposits aren't really relevant to the OP's situation of smokiness, I wouldn't have thought; more just general degradation of performance as the air intake path gets choked with debris.

Suspicion confirmed then...

 

Fuel additives usually contain cetane enhancers which allows earlier ignition of the fuel. Earlier and more complete combustion may help clear gunk from the cylinder down but won't do much upstream: if nothing else a bit more heat can burn stuff off. They may also contain detergent chemicals to remove deposits from the fuel system and clean up things that way so that the combustion event is cleaner.

@MikeHig my 2p with an older PD diesel (no DPF). I used forte diesel turbo cleaner + vpower and went WOT on a steep incline at motorway speeds (I find the M42 from the M25 is good for this).It needs to be run for a while at high temps and it may go into limp mode if it's been driven too gently. Engine restarts will get the power back.

 

 

Chum just messaged to say his car passed its MOT retest. His local garage changed the fuel filter and put in some Forte additive then he gave it a good thrashing. Result!

Many thanks for all the helpful advice.