MOT emissions fail

My 1996 110 300tdi has just failed its MOT due to emissions.

It's hardly had any use in the last few months and maybe this is the reason, perhaps it needs a good blast before getting it tested again? It does kick out a bit of black make on start up and under heavy acceleration.

Many years ago i did have the fuel pump tweaked to stop it being so sluggish, but its never failed previously.

Are there any injector cleaners I can squirt into the fuel tank that might help?
Could it be the injector pump?

You do need to blast it out. 2nd gear and drive it up to speed at high revs on the way to mot centre is how I do it. If still a problem, adjust throttle cable so it cannot rev so hard and put it back after test.

A few people on here have had good results with fuel additive too - I use Millers ECOMax. It mostly sounds like it needs a good blast to get it really warm and blow out all the crap.

I shall rebook the test and give it a blast, and add some Millers ECOMax.

Is this the stuff you use?

Give her some right foot

Works a treat

I use a double dose of wynns injector cleaner in half a tank of diesel and give it 30min of Italian tune up before the mot. has not failed yet. But as said above it is most likely due to lack of use, diesels like to be worked rather than cosseted along. Find a long section of steep hill, hook up 3.5 ton of trailer and go up the hill a dozen time with your foot to the floor. Should soon burn off anything and clean up the exhaust.

LeadFarmer said:

I shall rebook the test and give it a blast, and add some Millers ECOMax.

Is this the stuff you use?

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That's the stuff. It ups the octane rating of the fuel you add it to - you might notice a slight increase in power.

zeaphod said:

That's the stuff. It ups the octane rating of the fuel you add it to - you might notice a slight increase in power.

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Diesel doesn’t have Octane, but it does have Cetane.

LeadFarmer said:

I shall rebook the test and give it a blast, and add some Millers ECOMax.

Is this the stuff you use?

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I have used that stuff for a few years. I usually give it a double shot, then fill the tank right up. I have noticed the EGT’s are lower on a tank with this in as apposed to a tank without it. Not very scientific, as I didn’t record outside air temp and the likes, but around 40deg lower on dual carriageway speeds.

Brill, I’ve just bought some Millers Ecomax

Haven't got it in my hand as I type, but I think it’s a 50ml dose to 50L of fuel. I’m almost on an empty tank of fuel, would there be an advantage to squirting a half measure in now, as a concentrated dose, using up the fuel that’s in the tank and then filling as per the instructions?

LeadFarmer said:

Brill, I’ve just bought some Millers Ecomax

Havengit got it in my hand as I type, but I think it’s a 50ml dose to 50L of fuel. I’m almost on an empty tank of fuel, would there be an advantage to squirting a half measure in now, as a concentrated dose, using up the fuel that’s in the tank and then filling as per the instructions?

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I would suggest not as it is it looks to be a performance/economy additive. If it was a focused fuel system/injector cleaner then there would have been an advantage to a more concentrated does. But I have not used it so am happy to be corrected.

LeadFarmer said:

I shall rebook the test and give it a blast, and add some Millers ECOMax.

Is this the stuff you use?

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I've used that often, in my Freelander2 I usualy get slightly higher MPG with it in (according to the dashboard)

Would using premium/ultimate diesel help with the MOT?

+1 for Millers, works a treat.

LeadFarmer said:

Would using premium/ultimate diesel help with the MOT?

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It allegedly has more detergent in it. However, anything strong enough to clean injectors etc would surely also wreak havoc with seals etc? I don't know
If it worked, why are people in the business of injector cleaning?
Just my speculation

for the last 5 years mine has passed missions with no trouble then last year barely scrapped through,, which i put down to a lack of use as only doing local trips and only 1000 miles.
this year i put a bottle of the fuel cleaner in the tank a month before the test then on the morning gave it a good 20 min blast up the a23 then straight in for mot. and it barely had a score on the reading .. like it used to,, so i would say defiantly give it dose of fuel injector cleaner and give it a good blast ,, i always fill the replacement fuel filter with injector cleaner when i service it as well. think it had a reading .075.. last year was 1.2 i think and the pass is below 1.5 i believe

one year i filled up with one of BP special clean diesel fuels and in the morning it had cleaned the tank so well i lost half the tank of fuel
from a rust hole that opened up in the seam of the tank so i never used that again..

i just use the injector cleaner sold in wilkinsons. redexx i think it is ,, buy it when its on offer useually 2 quid a bottle then.. so nothing fancy

out of interest what exactly did it fail on..
hydrocarbons or smoke test

Hairball said:

out of interest what exactly did it fail on..
hydrocarbons or smoke test

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The MOT certificate says 'Emissions not tested', but that because as soon as they started testing it, it went off the record, maxed out their sensor.

LeadFarmer said:

The MOT certificate says 'Emissions not tested', but that because as soon as they started testing it, it went off the record, maxed out their sensor.

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... wow .. ive never heard of that before .. was it smoking heavily as well then. .
would have thought it would still have given some sort of a reading..
maybe if anyone on here that does mots, might be able to comment more on this as its not something ive heard of.

I take it you dropped it off warm and they tested the emissions straight away......

Mine recently passed and wouldn't be surprised if my tester pulled the hose of the back of the air filter to let it breath a little easier (we get on well).

Gmacz said:

adjust throttle cable so it cannot rev so hard and put it back after test.

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How easy is this adjustment, is it just loosening a bolt and moving the cable?