Smoke/emissions testing for diesels

Sputnik II · 28 Feb 2006 at 10:43

I took the Diesel for the mot yesterday at a local garage and when they did the emissions test they just held the throttle to the floor until either the rev limiter cut in or valve bounce occured. Personally I don't think this is either necessary or the correct way of doing it. In the past when I've took the car to the Ministrys own testing stations they rarely rev them past 4000rpm and on one occasion the ministry tester told me off for over revving the engine.
Does anyone know the correct proceedure they should use apart from the ' test it to destruction' method ?

jp7152 · 28 Feb 2006 at 10:56

They have to hold it against the limiter.

Dogbreath · 28 Feb 2006 at 13:39

If valve bounce occured then you either have a seriously high revving diesel or the valve springs have been taken from old biros, it simply won't happen. Diesels have a very low rev limit, unless the engine is at deaths door there is no problem with taking it up to the limiter.

Clarkey · 28 Feb 2006 at 13:56

wide open throttle is the correct procedure, if you dont like it then tough, your car wont get an MOT

cymatty · 28 Feb 2006 at 14:48

Do thet do the same for petrol engines?

thedazman67 · 28 Feb 2006 at 15:47

no just diesels i think, i think they do rev petrol cars, but not as far as the limit somebody clarifiy this for me.

thedazman

Sputnik II · 28 Feb 2006 at 16:48

Clarkey said:
wide open throttle is the correct procedure, if you dont like it then tough, your car wont get an MOT

If this is the correct procedure, then why don't the VOSA run testing stations do it that way?

Sputnik II · 28 Feb 2006 at 16:54

cymatty said:
Do thet do the same for petrol engines?

Unless things have changed a great deal since I was in the motor trade, Petrol cars have their emmisions checked at idle speed and normal running temperature. They might rev them slightly just to clear them before or during the emmisions is checked.
I'm not clear on the Diesel test because the firm I worked for back then only worked on petrol vehicles.

The_Dark_Side · 28 Feb 2006 at 18:39

Dogbreath said:
If valve bounce occured then you either have a seriously high revving diesel or the valve springs have been taken from old biros, it simply won't happen. Diesels have a very low rev limit, unless the engine is at deaths door there is no problem with taking it up to the limiter.

the difference with a diesel engine is many owners think their engine is killing itself when revved like this.diesels just sound that way when revved hard and no damage is being done unless you're low on oil.
unless i'm mistaken you physically cannot get enough fuel into a diesel engine to allow it to rev upto valve bounce.

energy · 28 Feb 2006 at 20:17

As long as its reasonably well maintained, with a good cambelt and up to temperature, a little revving won't do it harm, though I would probably cringe if it were my car/van on test.

I regularly redline my car when extracting maximum performance but sitting outside the car hearing it bounce off the limiter in neutral doesn't sound nice at all.

Sputnik II · 28 Feb 2006 at 20:29

I don't have a problem with the car being driven hard but, to hold it with the throttle full open and no load on the engine is neither sensible or healthy to the engine IMHO.
The other thing is its not really a true reflection on the cars emissions in normal driving because, in normal driving you never need to exceed 3000rpm.

Clarkey · 28 Feb 2006 at 20:44

Its the way it has been done for many years, it is not an issue.

Lopéz · 28 Feb 2006 at 20:49

Diesel engines are tested at full throttle. This is the only way of getting the correct reading. If you don't like it then buy a petrol, they are tested at idle and then for approx 40 seconds at 3-3500 rpm.

The_Dark_Side · 28 Feb 2006 at 22:08

Sputnik II said:
I don't have a problem with the car being driven hard but, to hold it with the throttle full open and no load on the engine is neither sensible or healthy to the engine IMHO.

if running without load damages an engine how are some engines "bench run-in"?

Sputnik II said:
The other thing is its not really a true reflection on the cars emissions in normal driving because, in normal driving you never need to exceed 3000rpm.

that's nonsense.
in a Turbo Diesel the turbo won't come on song until approximately 2500RPM.
obviously the engine needs to be tested to see what emmisions are like at the higher end of the rev range.

MrMoon · 28 Feb 2006 at 22:16

40seconds on the limiter is hardly gonna knacker your engine unless is a bucket of bolts in that case get a new car

Sputnik II · 28 Feb 2006 at 22:18

The_Dark_Side said:
if running without load damages an engine how are some engines "bench run-in"?

Probably because they ain't held at 6000rpm +

The_Dark_Side said:
that's nonsense.
in a Turbo Diesel the turbo won't come on song until approximately 2500RPM.
obviously the engine needs to be tested to see what emmisions are like at the higher end of the rev range.

Thats also nonsense because, the point of the turbo being 'on song' is dependant on the vehicle and its design etc. A nova turbo diesel comes on song at 3000rpm . A 16 litre truck engine would have a turbo spinning like a whirlwind at just 1000rpm.

Marshy · 28 Feb 2006 at 22:31

Opening the throttle on a diesel engine only regulates how much fuel is injected , the only way to test it's emissions is to inject the maximum allowed into the engine & that is ONLY going to happen at full throttle hence a diesel smoke test has to be done at full throttle, Some basic checks are carried out before the test is done which include oil level, bringing the engine up to normal running temp but most importantly the cambelt history has to be taken into account, The presenter of any diesel car should be given a card at reception stating what happens during the smoke test & if there is any doubt or the presenter can't confirm the cambelt history the testing station can & will refuse to carry out the test.

For the record the engine is held on the governor for aprox 5 seconds , if the smoke reading is within the limits after this time the car passes & thats it, this is known as "Fast Pass" , If if fails then the test is carried out up to a maximum of 6 runs & a mean average is taken , more often than not the first test run can be quite high especially if the car only pootles around as there is a buildup of soot in the exhaust which needs to be cleared out.

The_Dark_Side · 28 Feb 2006 at 22:42

Sputnik II said:
Probably because they ain't held at 6000rpm +

nor are 90% of diesels as they don't rev that high.
the amount of fuel fed to the engine determines how high it revs therefore you cannot rev a diesel past it's safe working limit.

Sputnik II said:
Thats also nonsense because, the point of the turbo being 'on song' is dependant on the vehicle and its design etc. A nova turbo diesel comes on song at 3000rpm .

notice the word APPROXIMATELY in my post.
now let's address your reply shall we?
according to you there is no need to rev higher than 3000 RPM in a diesel car.
if that's correct,and you are also correct in your Nova TD example then can you explain why the manufacturer constructed a vehicle with a turbo that according to you would be un-necessary to use?

Sputnik II said:
A 16 litre truck engine would have a turbo spinning like a whirlwind at just 1000rpm.

fairly obvious as many truck engines won't even rev to 3000 RPM

Sputnik II · 28 Feb 2006 at 22:52

The_Dark_Side said:
notice the word APPROXIMATELY in my post.
now let's address your reply shall we?
according to you there is no need to rev higher than 3000 RPM in a diesel car.
if that's correct,and you are also correct in your Nova TD example then can you explain why the manufacturer constructed a vehicle with a turbo that according to you would be un-necessary to use?

Erm, What I actually said is there is no need to rev MY car higher than 3000rpm because its passed the point of maximum torque produced. My car is normally aspirated so nothing exciting is gonna happen however hard its revved.
My point of comparing a Nova to a truck is that you can't generalise all diesel vehicles as being the same and having the same power bands.

tb2000 · 28 Feb 2006 at 23:04

The_Dark_Side said:
the difference with a diesel engine is many owners think their engine is killing itself when revved like this.diesels just sound that way when revved hard and no damage is being done unless you're low on oil.
unless i'm mistaken you physically cannot get enough fuel into a diesel engine to allow it to rev upto valve bounce.

If you take the governor off of a diesel engine (at least, on one's with the mechanical injection pump) then it would just keep climbing up the revs until self-destruction. Whether it would blow up before the valve bounce I'm not sure.