Diesel failed MOT on black smoke test- Help!!

in2deep_2

Providing the timing belt is well within its change limit it should be fine.
You will feel the engine pull back by itself when you reach the rev limiter, it really does need to go this far and you will see the soot pouring out if its well clogged up.

AdrianHi

Lots of good stuff here about filters etc.
Black smoke is essentially over-fueling - to much fuel to the air getting in. There can be a number of causes.
Another one to check is the crank case breather which can become blocked with gungey oil deposits and can be cleaned out relatively easily as a DIY job.
After that it might be time to get the engine management systems fault codes read with diagnostic equipment at the dealers or independent garage to see if that is logging anything.
Not sure if a diesel the age of yours has an EGR (Exhaust Gas Recirculation) valve, but this and the MAF (Air Meter) may also need a clean.
Lets hope it is not worn fuel injectors. A set of 4 would set you back somewhere in the range £700 to £1200, hopefully towards the bottom end of that scale for your car.

With a cleaner in as you have, half accelerator and near maximum revs is best, full accelerator and your just making it smoke as you are the cause of over fuelling.

Consider using an additive such as Millers Diesel Sport 4, helps to reduce smoke, has cleaning agents, improves fuel burn and ultimately saves a little money with reduced fuel consumption. You might notice a subtle performance improvement too. I use it all the time in my diesel and the only time you see it smoke is on full accelerator - and then it's only a little bit.

Pew_Pew_Pew_Lasers!

Soot is incompletely burnt fuel. Bad airflow, poorly spraying injectors, or faulty sensor leading to overfuelling. Could be any of those things.

There isn't much to go wrong on a diesel. Injectors can be easily cleaned, they must be removed and cleaned ultrasonically, and pop tested. Additives will not work.

Penny_Farthing_2

Thanks both. Adrian, how do I do half accelerator and near maximum revs. Is that the same as going at 60 - 70 mph in 3rd gear? Sorry - thick about cars.

AdrianHi

Penny_Farthing wrote: »

Thanks both. Adrian, how do I do half accelerator and near maximum revs. Is that the same as going at 60 - 70 mph in 3rd gear? Sorry - thick about cars.

I'm thinking when you do your accelerating, as a matter of course for a while use half accelerator and wait for high revs. In my diesel red line is 4800rpm, it simply will not go much beyond 4600rpm, 4200 rpm is high enough to change gear.

If you have a real dirt problem with the injectors this ultrasound treatment is the way to go. Additives like the Miller's I use are good for prevention, not a cure when you already have a more serious problem.

Penny_Farthing_2

Thanks. I agree the best thing is to fix the cause but I just don't have that kind of cash at the mo and the tax and isurance are due at the end of June so I need to push it through this mot if I can.
Off to find out what the timing belt changing interval is as my garage don't seem to have changed it inthe last few years.
Thanks again.

ianian99

change oil, oil filter , air filter etc and take it for an italian tune up on the way to mot test. http://articles.mbz.org/engine/diesel/italian/

the_big_fact_hunt

another trick is to slacken the accelerator cable off a bit to stop it revving so high

hewhoisnotintheknow

a nice heavy foot tune up is needed, take it for a nice motorwayy drive for 20 mins, then drop into 3rd for a bit so it revs highly, should clear it out

Quinny_2

Millers do one as well which I've used before.