NCT emissions on a classic car

Dkhuts

Just failed my retest on emissions.
Low idle CO 0.17%
HC 1780ppm
I dont really understand it but the ppm number seems through the roof
Car is a 1990 bmw 316 with a 2.0 litre conversion.
Will a simple change of the sparkplugs and some fuel addative help or is it fecked?

JoeySully

its not exactly that old, might be better posting in the regular motors forum

what year is the engine from?

https://www.bmw-driver.net/forum/ is also a good place for advice.

Tazio

had the same on an old Alfa with twin carbs - went from >1600 ppm to under 400 with new set of jets and a vacuum retune.

your engine is dumping too much much unspent fuel out its back pipe...

Depending on the technology in your engine ( I don't know this engine) it could be one of the following:

- plugs
- coil ( or coil pack)
- Distributor arm
- points (again don't know your engine) on older cars.
- leads
- poor grounding on engine block.
- newer car - air flow meter inaccurate - or if 'flap type' stuck open
- newer car - WOT sensor stuck to on (Wide open throttle)

Dkhuts

Not entirely sure of what year the engine is from but its from the same era, is a m20b20

w124man

One word ...... Dipetane!

unkel

w124man wrote: »

One word ...... Dipetane!

Or my preferred method.......an Italian tune up

Dkhuts

Tazio wrote: »

had the same on an old Alfa with twin carbs - went from >1600 ppm to under 400 with new set of jets and a vacuum retune.

your engine is dumping too much much unspent fuel out its back pipe...

Depending on the technology in your engine ( I don't know this engine) it could be one of the following:

- plugs
- coil ( or coil pack)
- Distributor arm
- points (again don't know your engine) on older cars.
- leads
- poor grounding on engine block.
- newer car - air flow meter inaccurate - or if 'flap type' stuck open
- newer car - WOT sensor stuck to on (Wide open throttle)

By vacum retune so you mean you got someone to basically tune the amount of air and fuel mixture? Id assume its not simple and would need someone who knows their stuff to do it. Ill try a set of new sparks first of all

JoeySully

Dkhuts wrote: »

By vacum retune so you mean you got someone to basically tune the amount of air and fuel mixture? Id assume its not simple and would need someone who knows their stuff to do it. Ill try a set of new sparks first of all

That is for carburettor engines i think. You have fuel injection so ecu decieds how much fuel the engine gets depending on throttle position and how much air in comming in.

The air intake hose are known to crack. Might be worth haveing a good look at it once removed.

Dkhuts

JoeySully wrote: »

That is for carburettor engines i think. You have fuel injection so ecu decieds how much fuel the engine gets depending on throttle position and how much air in comming in.

The air intake hose are known to crack. Might be worth haveing a good look at it once removed.

The car wasnt up to full temp when i brough it to nct as i live 3 mins away, that could be a factor too. Ive the NCT booked for next week and hoping that a set of new sparks, removing the air filter, and some diptane with high rev driving will do the trick

Bigus

Dkhuts wrote: »

The car wasnt up to full temp when i brough it to nct as i live 3 mins away, that could be a factor too. Ive the NCT booked for next week and hoping that a set of new sparks, removing the air filter, and some diptane with high rev driving will do the trick

Not much point in going to that retest until you get it tested by a mechanic on a gas analyser first, otherwise it's just unscientific guess work, he should be able to find something obvious with the HC so high .

Dkhuts

Bigus wrote: »

Not much point in going to that retest until you get it tested by a mechanic on a gas analyser first, otherwise it's just unscientific guess work, he should be able to find something obvious with the HC so high .

Good call, bringing it to a mechanic day nefore the nct hopefully he solves it

w124man

Run a few tankful's treated with Dipetane through the system and make sure you drive the car for at least 20 miles on a good road to blow the cobwebs out.

Dkhuts

w124man wrote: »

Run a few tankful's treated with Dipetane through the system and make sure you drive the car for at least 20 miles on a good road to blow the cobwebs out.

Thats the plan but car has no tax or nct so dont want to be driving jt that much

unkel

Dkhuts wrote: »

Thats the plan but car has no tax or nct so dont want to be driving jt that much

Tax it so.

And print out your NCT appointment confirmation and bring it with you. Almost all gardai are reasonable people like the rest of us and they will have no problem with that. I presume the car is insured. Then take the advice several people gave you: take the car on a long spirited drive. And then put it through the NCT again.

The CO is really really *really* low for a car without a cat (I presume) indicating that it's running too lean at idle. That can result in high unburnt content (HC) due to resulting misfires. A good ballpark figure for CO should be about 1 or maybe a tad higher (seen as it's a relative modern engine just before the cats were introduced). For older cars 1.5-3.0 is more suitable.

Could it be a massive leak at the inlet side? Like a bit missing from inlet manifold gasket.

For a properly running engine that doesn't burn any oil CO 1.0 HC 100 is a good target. You are almost 20 times over in HC.

Kylie Fan

Hi Folks,
Similar issue, failed CO emissions at low idle of 4.05 vs 3.5 for a classic 998c mini (carb). HC emissions passed.
Is there any point in getting retest with a bottle of dipetane or equivalent plus having it warmer (oil temp was 28C)?
Would increasing the idle speed help?
Air and oil filters are new so don’t think they are the issue

Tuning the carb is last option If I need to find a mechanic who would do it.
Thanks

Seweryn

Kylie Fan wrote: »

Hi Folks,
Similar issue, failed CO emissions at low idle of 4.05 vs 3.5 for a classic 998c mini (carb). HC emissions passed.
Is there any point in getting retest with a bottle of dipetane or equivalent plus having it warmer (oil temp was 28C)?
Would increasing the idle speed help?
Air and oil filters are new so don’t think they are the issue

Tuning the carb is last option If I need to find a mechanic who would do it.
Thanks

You should be able to easily reduce the CO by making sure the engine is fully warmed up and being driven for say 20 km before the test. I would also take it for a bit longer spin some time before the re-test. You can increase the idle speed to about 1200 rpm (this on its own could do the trick). No harm to put some Dipetane for extra help.

hi5

It could be the fuel/air mixture, there is usually a screw on the carb to adjust this.
You will need a vacuum gauge, lean out the mixture until you have maximum vacuum.

https://www.raygrahams.com/products/55477-draper-59075-vacuum-and-fuel-pump-tester.aspx?pv=25513&currency=eur&gclid=CjwKCAjw8LTmBRBCEiwAbhh-6PerxbRaiTTTtLD3P22bnEVB6k2UAJ7wndvNVuO0CP3Kz-dFdSA7DxoC2F0QAvD_BwE

Kylie Fan

hi5 wrote: »

It could be the fuel/air mixture, there is usually a screw on the carb to adjust this.
You will need a vacuum gauge, lean out the mixture until you have maximum vacuum.

https://www.raygrahams.com/products/55477-draper-59075-vacuum-and-fuel-pump-tester.aspx?pv=25513&currency=eur&gclid=CjwKCAjw8LTmBRBCEiwAbhh-6PerxbRaiTTTtLD3P22bnEVB6k2UAJ7wndvNVuO0CP3Kz-dFdSA7DxoC2F0QAvD_BwE

Thanks, I wouldn’t be confident on whether i would make it worse or better without being able to measure the emissions. I have heard you can judge it by the condition of the spark plugs but I don’t really have experience of doing it.

As carbs are probably only on cars that are nearly 30 years old would most mechanics( at least ones under 40) be familiar with tuning them, probably simple enough job when you know what your doing?

kadman

Was the original carb from the 2 litre setup fitted.

Seweryn

Kylie Fan wrote: »

Thanks, I wouldn’t be confident on whether i would make it worse or better without being able to measure the emissions. I have heard you can judge it by the condition of the spark plugs but I don’t really have experience of doing it.

As carbs are probably only on cars that are nearly 30 years old would most mechanics( at least ones under 40) be familiar with tuning them, probably simple enough job when you know what your doing?

I wouldn't give that job to anyone unless he uses proper equipment, i.e. an exhaust gas analyser. Otherwise I can do it myself with just as good results.

Seweryn

Seweryn wrote: »

I wouldn't give that job to anyone unless he uses proper equipment, i.e. an exhaust gas analyser. Otherwise I can do it myself with just as good results.

For carbs there maybe specs like "Fully close the mixture screw and open by 2.5 turns" to get it to a right ball park. I'm almost ready to bet that, as the CO is just a tad over the limit, by just closing the mixture screw (if fitted, could be hidden behind a tamper proof seal) by a small amount (1/4 - 1/2 turns) would be enough to make the Mini pass.

In general the good rule of thumb is that idle mixture screw should be turned to where the idle speed is the highest and the idle screw then turned until you reach a specificed idle or if not specified to 900 rpm +/- 50 for most of the engines that rev up to 5000-6000 max. Alternatively adjust to close to minimum where the engine still runs smoothly with headlights on.