NCT emission testing and reeving the engines

Xpro

Some time ago I had a 320d Auto in for an NCT, while I observed the NCT tester reeving the absolute life out of the engine, for a solid 30ish seconds and probably in 2/3 cycles.

Now, the car is 2012 model with DPF fitted and the exhaust tailpipe is spotless clean showing the clear stainless steel.
A blind man would see there was zero smoke coming out of that exhaust.

Interesting part is I did some inquires into the emission testing and various requirements.

The NCT manual states the following:


15. To initiate each free acceleration cycle, the throttle pedal must be fully depressed quickly and
continuously (in less than one second) but not violently, so as to obtain maximum delivery from the
injection pump.
16. During each free acceleration cycle, the engine shall reach cut off speed or, for vehicles with automatic
transmissions, the speed specified by the manufacturer or, if this data is not available, then two thirds
of the cut-off speed, before the throttle is released. This could be checked, for instance, by monitoring
engine speed or by allowing a sufficient time to elapse between initial throttle depression and release.



So basically its in their manual to hit the limiter/redline while they are performing the test..


Quite contrary to what some manufacturers actually state:

As BMW related, this are BMW testing files

- Emissions test instructions for BMW Group vehicles with petrol engines
- Emissions test instructions for BMW Group vehicles with diesel engines
- Emissions test instructions for BMW Group vehicles with alternative drives

Effective check by means of exhaust tailpipe measurement :

7. General – covering all engine designs
Exhaust emissions test on vehicles with automatic transmissions
Vehicles with automatic transmissions may suffer failure of their multidisc clutches during
exhaust emissions test if the test steps take up too much time at higher engine speeds.
This concerns in diesel engines primarily the checking of the “maximum speed at no load” if
it takes longer than 1.5 seconds and in petrol-engine vehicles with oxygen sensor emissions
control (closed-loop-controlled catalytic converter) if the conditioning phase of 3 minutes is
applied at n => 3000 rpm.
This damage is caused by the high pressure in the hydraulic fluid circuit at engine speeds
above approx. 2500 rpm, which results in a pressurization of the clutch discs by way of leaks
due to operation or wear. The linings of these clutches are subject to increased wear with the selector lever in position “P” or “N” and the output shaft or rear wheels stationary.

engine = 2500 rpm --> max. 15 minutes
engine = 3000 rpm --> max. 60 seconds
engine = 5000 rpm --> max. 1.2 seconds

In the case of other automatic transmissions, the dwell time at higher engine speeds
( > 3000 rpm) must be limited to the absolutely necessary level.


The extract above was specifically for diesel BMW engines.

I'm not going to quote other stuff, as some of its quite similar, but this would give a general idea on poor testing standards in Irish NCT test centres.
No wonder there are so many engine failures and snapped belts during the test.
One would wonder how an MOT system works in UK, while most cars with DPF filters are only inspected visually and via the OBD as smoke tests on these cars are pointless, never mind revving the stones out of the engines..

demanufactured

It won't do any harm to the engine.
Where are you hearing of snapped belts during tests?
I've literally never heard of it.

JimmyCrackCorn

demanufactured wrote: »

It won't do any harm to the engine.
Where are you hearing of snapped belts during tests?
I've literally never heard of it.

Unless your car is already broken no harm in revving the engine.

If your bet pops off with no load on the engine it wasn't right to begin with.

mickdw

I would generally be of the school of thought that says if it breaks during testing, it was ready to break anyway however, if they are exceeding manufacturer recommended limits, that is a different story and should be strongly queried.

wonski

I am not really sure the manufacturer's guidance on how to test emissions is the one to be followed.

If the engine can't take a bit of revving once every two/one year then it says something about the manufacturers as well.

jimgoose

JimmyCrackCorn wrote: »

...no load on the engine...

Isn't that the truth. Thus rendering the test as currently implemented completely pointless on anything vaguely modern. :pac:

demanufactured

jimgoose wrote: »

Isn't that the truth. Thus rendering the test as currently implemented completely pointless on anything vaguely modern. :pac:

Yep,
Should be on a rolling road with some back force.

Xpro

I know some might think you can rev the car stationary and nothing will happen, that might be that case,but it’s certainly not good for any engine to produce high rpm without any kind of loading, besides with current diesels its totally pointless.
If you look at the newer VAG engines, all are electronically limited to 2500rpm stationary, you just cant hit the higher revs in N as it wont allow you. Probably a good reason for it too.

1874

Always been a bit wary of this myself, but they make you sign a disclaimer, how would you prove they over did things ie revving excessively? or disprove their likely assertion that the belt was on the way out?
Can you limit different cars to prevent excessive revs? older petrols or diesels? Ive an older diesel and I would like the option to prevent them from overdoing it.

CJhaughey

1874 wrote: »

Always been a bit wary of this myself, but they make you sign a disclaimer, how would you prove they over did things ie revving excessively? or disprove their likely assertion that the belt was on the way out?
Can you limit different cars to prevent excessive revs? older petrols or diesels? Ive an older diesel and I would like the option to prevent them from overdoing it.

mechanical or electronic throttle?

1874

CJhaughey wrote: »

mechanical or electronic throttle?

I believe its an electronic throttle 01 octavia diesel, in good nick, know the date of the timing belt change etc, may fail on something else, but Id rather they did not try kill it outright.

lalababa

Another question; why do they attach two clamps with wires to the battery? I've seen them do it.

I put my diesel passat throught the uk MOT last week.The engine was wasn't revved at all.Emissions test is done at idle

Squidgy Black

1874 wrote: »

Always been a bit wary of this myself, but they make you sign a disclaimer, how would you prove they over did things ie revving excessively? or disprove their likely assertion that the belt was on the way out?
Can you limit different cars to prevent excessive revs? older petrols or diesels? Ive an older diesel and I would like the option to prevent them from overdoing it.

You could fit an aftermarket rev limiter, or else change it in the map on the ecu.

Wouldn't really be worth the effort, revving a car to red limit for a very short period of time shouldn't cause much damage.

teediddlyeye

lalababa wrote: »

Another question; why do they attach two clamps with wires to the battery? I've seen them do it.

That's how the machine reads the rpm.

As others have said if you're engine breaks during the nct there was something wrong to begin with. Your car should be able to rev to the redline no problem.

If the nct tester is holding the revs high it could be because the machine is reading too low a temp or the cat needs to be purged.

Either way generally the tester is usually trying to make it pass not fail 😉

mikeecho

My auto Diesel BMW, often revs at over 3k while driving /accelerating for well over 30secs while in sport mode.

It hasn't blown up (yet) .. so I doubt that a few revs under no strain at the NCT centre would be an issue.

1874

mikeecho wrote: »

My auto Diesel BMW, often revs at over 3k while driving /accelerating for well over 30secs while in sport mode.

It hasn't blown up (yet) .. so I doubt that a few revs under no strain at the NCT centre would be an issue.

Some posters have mentioned this is done under no load, a different situation and seem to suggest that that in itself may cause a problem and not benefit an emissions test anyway. At times i might floor it and the revs go fairly high, I dont think thats a harm itself that cannot be tolerated, but I wouldnt stick it in neutral and redline it.

Xpro

Exactly, the engine is designed to rev when under the load, but its a quite different scenario when you rev your engine stationary. Its like pedaling your bike with the wheels up and the chain and gears are bouncing up.

Anyway, the moral of the post is why NCT have a generic regulations to rev the cars to the limiter for smoke testing while car manufacturers are recommending differently and especially on latest DPF cars. It makes no sense.

As I work in the motory industry, we had a few failures of cars during the NCT test. And I wouldn’t say the cars tested were in poor shape.

Granted, we had an N47 320d breaking a chain during the emissions testing, while they are know for chain failures, so clearly an underlying issue.
14 Ford Mondeo broke a belt under high rpm, full dealer history and 67,000miles.

Quick google and boards search will revel even more of those issues.

And theres a reason why NCT make you sign a declaration, cause they know it well, cars can go pop, as it happens and they refuse to take the responsibility

rex-x

Xpro wrote: »

Exactly, the engine is designed to rev when under the load, but its a quite different scenario when you rev your engine stationary. Its like pedaling your bike with the wheels up and the chain and gears are bouncing up.

Anyway, the moral of the post is why NCT have a generic regulations to rev the cars to the limiter for smoke testing while car manufacturers are recommending differently and especially on latest DPF cars. It makes no sense.

As I work in the motory industry, we had a few failures of cars during the NCT test. And I wouldn’t say the cars tested were in poor shape.

Granted, we had an N47 320d breaking a chain during the emissions testing, while they are know for chain failures, so clearly an underlying issue.
14 Ford Mondeo broke a belt under high rpm, full dealer history and 67,000miles.

Quick google and boards search will revel even more of those issues.

And theres a reason why NCT make you sign a declaration, cause they know it well, cars can go pop, as it happens and they refuse to take the responsibility

There is zero chance that the nct test is damaging an already healthy vehicle. If you had a belt or chain snap then they were already going to snap! The reason for the disclaimer is because of so many playing timing belt roulette

Del2005

Xpro wrote: »

Anyway, the moral of the post is why NCT have a generic regulations to rev the cars to the limiter for smoke testing while car manufacturers are recommending differently and especially on latest DPF cars. It makes no sense.

The manufacturers don't set the emissions limits or how they are tested.

We've seen what happens when they get a bit of lee way with the fuel efficiency standards they gamed and the anti test software they installed.

Xpro

Del2005 wrote: »

The manufacturers don't set the emissions limits or how they are tested.

We've seen what happens when they get a bit of lee way with the fuel efficiency standards they gamed and the anti test software they installed.

Every one of them they do. Just look at brits and their emissions testing. A much higher standard and accuracy.

Btw, the software cheats and all that stuff that went on, certainly wouldn’t be discovered by an NCT , as cars with DPF filters produce no smoke anyways regardless of what their emissions are.

w211

Here in Ireland they do not torture the engines. They perform the test only around 3000rpm and the testing time are relative short. The brakes testing they take bit longer time to warm the brake system and then they get the good readings. Almost brakeles car can too pass. They do not work against you.

Del2005

Xpro wrote: »

Every one of them they do. Just look at brits and their emissions testing. A much higher standard and accuracy.

Btw, the software cheats and all that stuff that went on, certainly wouldn’t be discovered by an NCT , as cars with DPF filters produce no smoke anyways regardless of what their emissions are.

The UK who used the NCT as a template for the MOT in Northern Ireland. The MOT is riddled with corruption.

The software cheat was an example of why they don't get to set the testing standards. What was being tested is immaterial.

chicorytip

teediddlyeye wrote:

If the nct tester is holding the revs high it could be because the machine is reading too low a temp or the cat needs to be purged.

teediddlyeye wrote:

Either way generally the tester is usually trying to make it pass not fail 😉

Entirely accurate. Good points.

mikeecho

If an engine fails because it was revved in neutral.. doesn't say a lot for the engine.

Can I go to a main dealer, ask for a test drive, rev the car in neutral and expect it to explode...

There is obviously a problem with an engine if it is unable to withstand a short term stress.

sunnysoutheast

Was the concern detailed by BMW in the original post not about clutch wear at high engine revolutions in P or N rather than the engine failing?

I'm on the phone so can't post and read it at the same time!

I'm not sure if it's a concern with torque converter transmissions or just DSG/DCT etc . given it talks about multiplate clutches.