Failed MOT on emissions - some numbers for those who know mo

[Paul]

Evening all,

My 3.9 V6 Dodge failed its MOT rather drastically today...



Not even close to passing.

It failed a couple of months ago, and the OBD flagged a P0155 - bank 2, sensor 1 o2 sensor fault.

Replaced that and it failed even more drastically today 🤣

The P0155 has returned

So I went out and did a good Eyetalyan tuneup (10 miles at 50mph in 2nd😁) took my little computer and did some data logging which I'm hoping someone can make sense of:

At cold the voltage cycles are as below.

02s11 cycles 0.84 to 0.06
O2s12 cycles 0.78 to 0.12
O2s21 cycles 0.86 to 0.06
O2s22 cycles 0.76 to 0.72

When warmed up all cycle 0.74-0.82 (which is definitely rich) except O2s21 which is still sending wacky voltages from 0.3-0.76 volts



Short term fuel trims confirm the rich running:

SHRTFT11 0%
SHRTFT12 99.2%
SHRTFT21 0%
SHRTFT22 99.2%

EDIT: Or not, B1S2 and B2S2 are downstream of cats and will always show 99.2% apparently, and aren't relevant. So I think these numbers are actually healthy?

Coolant temp sensor seems accurate, showing 205 Fahrenheit when warmed up.

Is the new o2 sensor a dud? Could this be causing the rich running? All thoughts welcome 🙏

[mk2cossie]

Narrow band sensors should fluctuate fairly quickly between 0.1 and 0.9 volts when up to temp.

Also, is the Dodge an SUV or pickup? If so, they aren't treated to the same passenger car emissions test as 80% of normal cars

[Paul]

I'm wondering if my cheap OBD reader isn't keeping up with the rapid fluctuations.

Definitely a pickup - wonder if they know about this at my garage. I doubt it since I've got an advisory for corroded rear coil springs which look decidedly long and flat and leafy to me...

[jimi]

Have you tried searching for your VRM on the government vehicle check website (or the MOT history one) ? if not give it a try on both

[Rich]

Oct 31, 2023 22:13:43 GMT Paul said:

Definitely a pickup - wonder if they know about this at my garage. I doubt it since I've got an advisory for corroded rear coil springs which look decidedly long and flat and leafy to me...

That’s just one mouse misclick as coil and leaf are listed next to each other on the MTS. However, it’s not great practice. Does the truck have twin exhausts to the rear? If so the emissions test should be carried out twice, on each engine bank and the emissions results averaged. The downstream sensor with a voltage swing would appear you have a failed or failing cat on that bank.

[pow]

Low Lambda reading and high CO would suggest rich running to me - any evidence of that?

[pow]

Sorry I should read the whole post shouldn't I!

I'd start with anything that measures air in and exhaust out - sensor wise. Mass air flow or manifold pressure? Other things like ignition timing as well would have an effect, mullared plugs?

[Paul]

Plugs don't seem to show anything majorly untoward (don't ask about number 6 pls I bounced it off the bonnet, chipped my paint then smashed it on the ground)


I'm going to chuck a bottle of cataclean in and hook around at midnight for 15 minutes in 2nd gear.

I'm wondering if it's a clogged cat on the bank 2 side...have ordered a back pressure tester on Amazon so will give that a whirl tomorrow.

Have also ordered another pair of o2 sensors which a friend who happens to be in Boston right now will bring me back this Sunday.

[tuckers1954]

is your vehicle in the emissions book ? i think its available on line , if its not a factory import from new there are no figures for it and it wont be in the emissions book and is therefore a default test , ie non cat , look it up lts of garages get it wrong

[Rich]

Nov 9, 2023 16:36:18 GMT tuckers1954 said:

is your vehicle in the emissions book ? i think its available on line , if its not a factory import from new there are no figures for it and it wont be in the emissions book and is therefore a default test , ie non cat , look it up lts of garages get it wrong

Not quite.

Personal imports
A personal import must be tested according to its date of first use. However, if you’re shown a letter from the vehicle manufacturer proving that the engine does not meet British emission standards you must test to the next lower emission standard.

For example, a 1995 car first used in Gambia with a letter from the engine manufacturer stating the engine number and showing that the engine cannot meet catalyst emission limits, you must use the non-cat limits of carbon monoxide (CO) 3.5% and hydrocarbons (HC) 1,200ppm.

www.gov.uk/guidance/mot-inspection-manual-for-private-passenger-and-light-commercial-vehicles/8-nuisance#section-8-2-1

However Paul...

Passenger cars
A ‘passenger car’ is a vehicle that:

is constructed or adapted to carry passengers
has up to 5 passenger seats, excluding the driver’s seat
has a DGW not exceeding 2,500kg
is not a goods vehicle, such as a pick-up or a car-derived van
If you’re not sure if a vehicle is a passenger car, you can confirm it by:

getting the DGW from the manufacturer’s VIN plate
checking if the vehicle is listed in section 2 of the current emissions data book
checking the owner’s handbook or a data book
If you cannot find proof that the vehicle is a passenger car, you must assume it’s not a passenger car.

Chart 3. Emissions limits of non-passenger cars first used on or after 1 August 1992

[mk2cossie]

Nov 9, 2023 19:39:36 GMT Rich said:

Nov 9, 2023 16:36:18 GMT tuckers1954 said:

is your vehicle in the emissions book ? i think its available on line , if its not a factory import from new there are no figures for it and it wont be in the emissions book and is therefore a default test , ie non cat , look it up lts of garages get it wrong

Not quite.

Personal imports
A personal import must be tested according to its date of first use. However, if you’re shown a letter from the vehicle manufacturer proving that the engine does not meet British emission standards you must test to the next lower emission standard.

For example, a 1995 car first used in Gambia with a letter from the engine manufacturer stating the engine number and showing that the engine cannot meet catalyst emission limits, you must use the non-cat limits of carbon monoxide (CO) 3.5% and hydrocarbons (HC) 1,200ppm.

www.gov.uk/guidance/mot-inspection-manual-for-private-passenger-and-light-commercial-vehicles/8-nuisance#section-8-2-1

However Paul...

Passenger cars
A ‘passenger car’ is a vehicle that:

is constructed or adapted to carry passengers
has up to 5 passenger seats, excluding the driver’s seat
has a DGW not exceeding 2,500kg
is not a goods vehicle, such as a pick-up or a car-derived van
If you’re not sure if a vehicle is a passenger car, you can confirm it by:

getting the DGW from the manufacturer’s VIN plate
checking if the vehicle is listed in section 2 of the current emissions data book
checking the owner’s handbook or a data book
If you cannot find proof that the vehicle is a passenger car, you must assume it’s not a passenger car.

Chart 3. Emissions limits of non-passenger cars first used on or after 1 August 1992

And following that chart (and presuming the Dodge is 2001 from the reg) then its 3.5% CO, and less than 1200ppm HC

[Paul]

Little epilogue as I forgot all about this once I'd fixed it...not very exciting though.

Turns out the O2 sensor I'd replaced was itself a dud. Swapped it out - again - with a part a friend of mine brought back from a business trip to the States and all was well.

Another year's happy motoring awaits 😀

[swampy76]

Those Bosch super 4 plugs arnt the best either
I had a mini in at a rolling road ( hi tec motorsport in Bradley heath)and it was doing all sorts of weird things , swapped the plugs out for a set of standard single electrode NGK ones and not only did it start running right it picked up power as he could tune the carb properly ( yellow spring and a custom ground needle)