Running Rich, failed MOT

[Shottymonster]

i've just come back from my MOT, and with a few minor defects, my Leon 2004 1.4 failed on emmissions, mainly its running rather rich at fast idle.

Co was 1.43% (limit is 0.2%)
and Lamba was 0.958 (needs to be between 0.970 and 1.030)

i've no engine light on, and i've just ordered an OBD11 because my old code reader wont work on newer motors to see if there are any hidden codes but are there any "common" or simple things i should check??

 

[adam davies]

i've just come back from my MOT, and with a few minor defects, my Leon 2004 1.4 failed on emmissions, mainly its running rather rich at fast idle.

Co was 1.43% (limit is 0.2%)
and Lamba was 0.958 (needs to be between 0.970 and 1.030)

i've no engine light on, and i've just ordered an OBD11 because my old code reader wont work on newer motors to see if there are any hidden codes but are there any "common" or simple things i should check??

This is mk3 forum 2012 an on

 

[Shottymonster]

This is mk3 forum 2012 an on

Sorry typo, it's a 2014 1.4 fr, I'll update the post

 

[cupra14]

Check OBD status to see if it's running CL (closed loop) - it may well not be and if not will run rich because it dare not run lean (engine destroyer).

Ideally an engine will be OL (open loop) when cold but rapidly (e.g. 30 secs) switch to CL.

If running CL, look at fuel trims (STFTs & LTFTs) with a hot engine, parked, at idle. (Hot so that the O2s should be working.)

A dirty MAF (if your car has one) can be a cause but don't assume - get data.

As well as checking for codes (DTCs) also check for pending ones.

 

[Shottymonster]

So running in CL

Intake pressure at idle 33kpa
LTFFT was 2.4%
Couldn't see a short term one?

I did notice that my O2 sensor post cat was 0.66v fluctuating slightly but my O2 sensor bank 1 sensor 1 was 0.00v with no movement.

I have no fault codes other than a few old misfire ones.

 

[cupra14]

I don't know your engine but usually the pre-cat O2 is a wideband (they are measured via current so your OBD tool needs to report that way) and the post cat the other (ahem, cheaper!) kind (using voltage).

Widebands shouldn't constantly fluctuate (whereas the other kind pre-cat will). Post cat O2s shouldn't fluctuate much (because the burned fuel mix that's been through the cat should be pretty much consistent and OK as regards O2/HC - granted yours isn't at the moment).

The car can only measure O2 so if there's too much fuel (or it doesn't burn properly) you can have an apparently OK LTFT yet things are not OK.

(Ideally they'd also fit fuel-measuring sensors but exhaust gas is hot and horrid and I don't think there are any affordable and robust fuel sensors, so we make do with just O2s.)

An LTFT 2.4% means there's a tiny bit too much O2 (according to the sensor(s)) so it's adding a tiny bit of fuel - I'd say that's not helping but not the problem.

So... you get to engage brain for what can fit the above. My feeling is incomplete combustion so a problem with spark plugs (old? wrong ones?), or coil(s) (e.g. not firing properly), er... or maybe something I've not thought of.

BTW, if you have a tune or any mods at all start by suspecting them!

 

[Shottymonster]

Hmmmm i did change the plugs about a month ago with what the NGK site recommended PZKER7B8EGS, could possibly be a bad batch but I will double check the coils are attached and that the plugs are tightened down ( I'll take one out and see what the tips look like)

I did notice throughout the winter when I was driving there was alot of what I thought was condensation from the exhaust at standstill even after a long drive but I just put that down to the cheaper petrol with more ethanol in it now. Could be a red herring, I'm not used to modern petrols, been a derv man for the last 10 years.

No mods that I know of, certainly not by me and the previous owner said she never had it mapped either (she's an old friend) and she's had it 5 years ish with no reports of emissions on the MOT's

I ordered a pre-cat O2 anyway which is sat awaiting parts as I'm away for a few day, seatparts site listed them both at the same price of £230 each but that doesn't mean ones more advanced than the other I guess.

Not have emissions issues on a car since I had an old classic mini all this modern tech is new to me fueling wise.

 

[Shottymonster]

So I had a play when I got back (they sent the wrong lambda sensor, they sent a 4 pin not a 6) so I had a play with some other bits.

Checked plugs for security and looks, couldn't see anything there. Cleaned the sensor on the manifold and intake. Re-secured the air filer housing as one of the clips is broken so secured it with a cable tie (and checked the screws underneath the housing)

Ran up to temp again and get a long term trim of 0.6ish, then if I blip the throttle and let it settle it sort of goes up to 2 ish then comes back down to eventually settle at 0.6 again.

Is 0.6 a more acceptable figure? Maybe it was a dirty sensor.

 

[cupra14]

2.4% is ok. So is 0.6% (if you meant that).

But always bear in mind the car cannot see fuel (HC) left in the exhaust gas (can't see NOx either). So it's using O2 and so long as the air/fuel mixture is in the right ratio and also burns properly that is fine. Your MoT shows things were not OK at that time - the MoT here (UK) can (& does) measure HC and so on (using costly sensor(s)).

It figures the ratio by trusting the air coming in (MAF sensor, typically) and knowing how much fuel is needed for that air (O2, that is) - which means it has to trust the fuel injector(s) deliver that amount.

 

[Shottymonster]

Ahh I see, well the HC was within the limits when it was on the tester, just the co and lambda were out so it must be burning it correctly, just not at the right ratio? (If it was plugs or coils then would it be a poor spark and a high HC?)

So possibly the slightly insecure airbox or a dirty sensor may be the issue then and throwing the ratio out, I guess without it going back in the machine again I'll have no way of knowing if I have fixed it or not. I'll chuck some injectors cleaner through it as an extra and then suck it and see, if not then it's going to have to be booked into a specialist as I'm at the limit of my knowledge unfortunately.

 

[MATT RILEY]

Common issue on the 1.4 failing mot with this, change probe 2 after the cat mate.

 

[cupra14]

Some garages will test just the emissions quite cheaply, rather than having to pay a full MoT fee

 

[mty12345]

The sensors post cat are there to measure the efficiency of the catalyst only, they do not affect the mixture.

Your Bank1 sensor 1 should have some voltage, and is the primary source of mixture control. I would highly suspect that is the issue, although how that isn't giving a fault code i don't know. I see you have already ordered one so i would imagine there is a high chance that will fix the issue.

 

[Shottymonster]

I think I got my wires crossed slightly on what I was looking for on the sensors.

My pre-cat is a wideband, so it's measuring current rather than voltage (I was looking in the wrong place on the scanner) and that gives me a lambda reading fluctuating between 1.001 and 1.01, and the current fluctuates a little, up to about 50mA if I remember right but it definitely has figures that are changing.

Google tells me a lambda reading of between 9.8 and 1.05 is fine which I am within (according to the car)

My post cat is reading 0.7v which again Google says is about right for post cat. (This fluctuates down to 0.2v if I rev the car and come back off the throttle but it then returns to 0.7 when back at idle after 5-10 seconds ish)

I did order a pre-cat sensor but they sent the post-cat one by mistake and I don't want to throw £200 sensors at it if it's not the issue because I can't send them back.

I'm going to run it a couple of days with some injector cleaner in there and then take it for a re-test, hoping that cleaning the MAF and the MAP sensor, and resecuring the airbox lid (one catch is broken) has done the job.

I'll come back and let you know the outcome (good or bad)

Thanks for all the info you have been throwing at me though, it's been a learning curve from what I'm used to.

 

[mty12345]

Yeah they work by measuring the current, but you should still have a voltage across them too. You can't have current flowing without a voltage, but i expect the ECU just doesn't measure the voltage and that's why it's showing 0.00v

If you haven't already paid for the sensor then yeah i agree, it's worth holding off for now and seeing if any of that helps first. If not then it could be that the sensor is failing and gving the car the wrong lambda reading. You'd only have to be off by a few mA to throw the lambda out by a certain percentage.

Good luck and definitely keep us updated, will be interested to know the outcome.

 

[Shottymonster]

Re-test done.

emissions passed with co of 0.01%, lambda of 1.00 which is a total change from what it was before.

unfortunatly im not 100% sure what fixed it which is a bit of a bummer. I could even still have a breaking down sensor and it just happened to be ok at time of re-test maybe.

but i want to thank you all for the input you gave, its been apreciated and saved me some pennies.

 

[mty12345]

Re-test done.

emissions passed with co of 0.01%, lambda of 1.00 which is a total change from what it was before.

unfortunatly im not 100% sure what fixed it which is a bit of a bummer. I could even still have a breaking down sensor and it just happened to be ok at time of re-test maybe.

but i want to thank you all for the input you gave, its been apreciated and saved me some pennies.

You're welcome. Glad to hear it passed without any issues.

 

[cupra14]

Great news - phew!