Emissions fail

[snodge182]

Hi all,

I have recently had an MOT failure due to the emissions test. (See attached photo)

I'm not sure what to make of this, as in one test the CO is fine but the lambda isn't, and in the other test the lambda is fine but the CO isn't.

Also to mention, I have this error code that keeps coming back (P0420), and using torque pro I also have the rich to lean failure come up within test results (see attached screenshot)

I'm not well off when it comes to money so I can't afford a garage to be diagnosing this, so I'm trying to do it myself.

Any idea what this is? I understand it could 1 of 4 things:

- Hole or leak in the exhaust

- Upstream O2 sensor malfunction

- Downstream O2 sensor malfunction

- Catalytic converter

 

I have tested the sensors as idle and at 3000 rpm. At idle, the graphs are both alike; moving up and down between 0.01 and 0.9. At 3000 rpm however, the downstream sensor becomes stable, while the upstream sensor continues its up and down readings.

 

Any help will be much appreciated.

 

P.S: also maybe worth mentioning, inside the cabin stinks of fuel when stationary with the engine idling (unburnt or otherwise) similar to a go kart or aftermarket motorbike exhaust.

[furtula]

Does it still smell like fuel when the car is warm? Might be it's just running lean due to 1st lambda sensor (from the engine side) being dead, but this should throw an error.

I have had lamba die/work depending on outside temperature, car temperature, so this might have happened to your car during the test.

 

What's your commute, do you die a lot of short trips and mostly city driving?

[snodge182]

When the MOT was done the car had been motorway driving right before for 2 hours.

When I did the test with the readings of the two sensors it had been running for an hour, and I had taken them with the engine running at 3000rpm for 2 minutes first.

During my normal use, I use the car for a 15 minute commute, morning and night, and short trips to the supermarket 5 minutes away

[furtula]

Haven't answered the 1st part of my question. If the answer is NO, then i would go back to motorway for some Italian tuneup.

[snodge182]

Sorry, yes it smells like fuel when the car is warm.

[flash22]

Does the car feel underpowered ? the O2 sensors need checking correctly with a meter, what are the fuel trims like ?? (short and long) if there is vac leak or the maf is reading incorrectly it will run very rich - What readings are you getting from the Maf at idle (up to temp)

It could need a CAT due to its age and mileage

[snodge182]

I'll check the fuel trims shortly using the torque app.

Also, regarding the MAF, I was looking for info on how to find it etc and this came up in the Toyota owners club:

"On 8/3/2010 at 10:54 PM, Jan van de Wouw said:

The Aygo does NOT have a MAF-sensor.

It relies on the MAP* and IAT* (which are actually combined into one and sit just befor the throttle valve) to determine

how much fuel needs to be injected. These values are then checked agains the O2-sensors and adjusted if neccesary.

*Manifold Absolute Pressue and Inlet Air Temperature"

Is this true?

 

I will post the trim results after warming the car back up and testing again

[snodge182]

So I have logged the fuel trim results (both short term and long term). It seems while one is never changing, the other follows a similar pattern to the O2 upstream sensor.

This is when the engine had only just started (and at idle):

 

And this is after the engine had warmed up to 86°C (and at idle):

 

I'd like to add at this point that a couple weeks ago/a month ago, I noticed trouble accelerating under high load. It seemed to be fine when driving normally but when I tried to push it to go fast and quick, it seemed a little like it was giving up (or even like it was out of fuel). Since then I filled up fully (with petrol of course) and added one dose of redex to it, as I thought maybe the injectors needed a clean. Since doing that it has been running fine again (fine as in performing under stress), but I'm wondering if any of that might have anything to do with these emissions issues.

 

P.S: I have since filled up with only petrol after running that tank down to reserve.

I also have one dose/shot of redex left that I can use.

 

[furtula]

When the car is warm, you should not smell gas, as it's not running lean anymore (as compared to cold car where the smell is pretty obvious).

I would suggest checking the 02 sensors with multimeter (if you have one), as it's one of the easier things to do.

[snodge182]

I'll have to source a multimeter, shouldn't be too difficult. What readings would I be checking for?

We have just done a 'block the rear of the exhaust' test, which seemed to create pressure within the exhaust system however there was a hissing sound coming from the engine bay at the exhaust outlet, so we are going to check that out for holes or other leaks.

To do this we are removing the front bumper for access 😣

[flash22]

The fuel trims look fine, my mistake about the MAF was thinking of another engine

As for testing O2 sensors you just need to check for resistance - but im leaning towards a blocked cat

You should be able to undo the top 02 sensor and look at the top of the cat

[furtula]

3 minutes ago, flash22 said:

The fuel trims look fine, my mistake about the MAF was thinking of another engine

As for testing O2 sensors you just need to check for resistance - but im leaning towards a blocked cat

Might be clogged cat, but how do you explain smell of unburnt gasoline, even in car,   when the car is warm?

Might be both tho, so take it out for a spin at 4k rpm on a highway 🙂

[snodge182]

Didn't think to visually check the catalytic converter, when we took the top sensor out we saw the mesh/grid type thing was blocked, so we have ordered a new cat from eBay.

Thank you so much for all the help, I will fit the new cat when it comes and reply with the result.

[flash22]

google is your friend for pics of bad cat's, hopefully you ordered the manifold and bottom gaskets too