As per the title my 2006 NC Sport has failed the MOT on emissions.
The results:
Fast idle test:
RPM Pass 2570rpm
CO limit .3% volume, Actual value 1.395%
HC pass 106ppm
Lambda. Required .970-.1.03 Actual .952 Fail
2nd Fast idle test:
RPM Pass 2599rpm
CO limit .3% volume, Actual value 1.181%
HC pass 49ppm
Lambda. Required .970-.1.03 Actual .960 Fail
Natural idle test. Required revs 620-820 not done as tester said idle was too high. I have since checked on my obd2 reader and tickover is 720rpm so I don’t know what happened there. Part of me [the hopeful part] suspects something amiss with their equipment or the engine was not fully warmed when the test was run hence the high idle and rich mixture
This test was done at a place I don’t usually use and does not have the capability to fix this as it’s primarily a tyre and exhaust centre but I had a voucher so…
My current plan is to run some fuel system cleaner through the system [& a mild Italian tune up] and give it another try at my usual place [they’ve already offered to check the emissions once the cleaner has done it’s stuff]. If nothing changes what do the experts here think might be the problem?
Hopefully an equipment issue as those readings are not good, none of them.
What is the car like on fuel? Problems with emissions are often quickly translated into increased fuel consumption.
The low lambda reading indicates a rich fuel mixture which likely has created the high hydro carbon readings and carbon monoxide. Both these are the result of incomplete combustion where too much fuel introduced as a ratio to the air to burn it. You pass on hydrocarbon but reading too high. I’m thinking it should be less that 30ppm.
The carbon monoxide level also indicates that the cat is not coping very well where the catalytic process should be converting this or the majority of it to water, CO2, etc.
If the equipment is correct, it would seem you need a precat lambda sensor but check the OBDII port for error codes. At that level of lambda reading the ecu is wrestling to deal with a failing lambda and there should be an associated error code stored. Checking the diagnostics may also show that something else is causing this scenario.
I hope this is simple to sort out but on the face of it serious emissions issues.
Low Idle CO 0,0,0,0 therefore below the measuring tolerance of the equipment.
Lamda 1.01,1.01,1,1
High Idle CO .01,0,0.01,0
HC 32,0,33,1
If the fault still persists on a second test, it is a game of parts darts and it could be the first Lamda sensor, the Catalyst, the mixture contol device, a bad connection or bad earth on the elecronic units etc.
I get 33mpg average using Shell 99 in mixed driving. I am expecting that to go up slightly since I changed the thermostat and the engine can now run at 86c rather than the 67c I was getting previously. I’ve not gone through a tank of fuel since the change yet so new data is not available. I feel that the long time running an engine that was too cool may have affected the cats ability to clean the exhaust gasses properly. The 2nd cat was replaced in 2017 for a similarly dire emissions test so I think that the thermostat was needing to be changed long before I got the car this time last year
New pre cat Lambda was my first though also. I’m resisting the urge to throw money at the problem until I get a better idea of what’s happening, my first instinct was to buy a new O2 sensor, maf sensor, and a new cat. That idle test not being done bothers me and makes me wonder if the car was properly warmed before the test.
I’ve checked the OBD2 and no emission related codes are set. No CEL illuminated but there is an ABS network error which I have not seen before. I’m hoping that’s got something to do with the MOT brake test.
I’ve taken a screenshot of my OBD2 app whilst the engine is running before it goes for a drive [waiting for the roads to dry, just waxed it]
My spend thrift urges have got the better of me. I’ve ordered a new front O2 sensor and a MAF. I’ll get the emissions checked before I open the packets so I can send them back if not required.
Our 56 plate 5 failed it’s mot yesterday miserably on emissions. Tester said it was way out and could not read anything and smelt oily. Car starts well and runs well, but could be the dreaded piston rings or PCV valve ?
Has anyone actually replaced the PCV valve and had success ? I also know its a pig of a job !
My first thought too but I made sure it was off before it went in and it was still off when it came out.
Just took it for a blast with the fuel cleaner in. Hello to the MK3 on the A602 who gave me the thumbs up. 70 miles later no codes in the computer and idle speed is still around 720 with the AC off.
MPG might suffer a bit this tank as I’ve been hooning around with a few more revs than usual to get the fuel system cleaner through. It’s been fun though.
I’m going for about 36 myself once I calm down a bit. I got 37 from one tank when I drove the length of the A1 and back in the same day.
Error codes are elusive. It would be nice to have the computer at least give me a hint but all the numbers look right. Afr 15-1 and a reading of 1.0 from the O2 sensor. all are what I would expect. You would think if the CO reading was that high that the second O2 sensor would be moaning but the car seems happy and content with the world.
Quote. “ Just took it for a blast with the fuel cleaner in. Hello to the MK3 on the A602 who gave me the thumbs up. 70 miles later no codes in the computer and idle speed is still around 720 with the AC off. “
Not wishing to cause problems, but if the car has failed the MOT, under the new rules, does that not mean you are driving it illegally?
As I say, not criticising, just interested in the legal position under the new rules.
D
Looking online it says that as long as the current ticket is valid you can drive the vehicle if the failure was not due to a dangerous fault https://www.gov.uk/getting-an-mot/after-the-test. The car still has to be roadworthy which means that it has to be safe to drive. No mention of the emissions in the roadworthy section on the government website https://www.gov.uk/check-vehicle-safe The failure sheet says to repair immediately which is what I am doing by running the stuff through it after advice from a garage. If this has repaired it then [it’s hard to know, who has the money to have another MOT done after every new substituted part goes in?] I have nothing to say that I need proof of that until the old ticket expires. If it were a dangerous fault then obviously I would not be driving it but I would most likely know the fault and would have already fixed it. These “it might be this” faults are the worst.
EDIT: FWIW the car breezed through the rest of the test without advisories
An update. I’ve been messing around with the torque app and checking various sensors. I found that the O2.1x2 sensor voltage (post cat sensor) was reading 0.9v. At first I thought this was normal but on further investigation discovered that it should read 0.45v when presented with a fuel mixture of 14.7 to 1. I replaced this sensor when I first got the car so assumed it was okay and therefore the mixture is in fact rich just as the mot emissions indicated. The fuel treatments were having no effect and a cleaning of the maf had little to no effect either. I bit the bullet and opened the packet to the front o2 sensor I received on Friday. The old one came out really easily once I’d worked out how to access it and the new one went in with little fuss and very little torque applied. I took the opportunity to change the oil while it was up on stands and spent some time swearing at the oil filter positioning, what I wouldn’t give for a four post lift!
A quick test drive confirms that the old sensor was at fault, the new reading on the post cat sensor spends most of its time at under 0.1 with peaks as high as.0.9 when I get really heavy footed. Another mot is booked for Tuesday, I feel pretty confident it will breeze through the emissions now.
I filled up with fuel and have been getting 33mpg (bang on average for this car) since changing the thermostat despite thrashing it to get the fuel additive through which is pleasing. Now it’s not housing fuel into the engine like its going out if fashion I hope for 35mpg plus
Thanks to everyone for their input, I’ll let you know what happens on Tuesday
Got the car home and I went crazy and opened the packet to the new MAF sensor I bought the other day. Fitted in moments. Then I removed the + battery terminal for 30 seconds or so to force the ECU to relearn some things. My thinking behind that being that it has been struggling with a dodgy front o2 sensor and an under cool engine for a while so all it’s previous learnings might not suit the new situation it finds itself in. No codes stored in ECU when first started. Adjusted the Torque app on my phone to show AFR both measured and commanded, rear o2 readings, EGR operation as well as the usual revs and temp. Went for a drive. No pending codes when I stopped after a few miles. EGR seems to be working and the rear o2 sensor is showing between 0.5 and 0.9 in normal driving and in the .4 region when under large throttle openings and higher revs. I think the high reading on the rear o2 is something to do with the EGR operation, if the exhaust gas is being recirculated then the amount of oxygen in the exhaust is going to be lower i think maybe who knows?!?!? Another 50 miles on top and still no codes pending or otherwise. Another drive to work tomorrow, lets hope it remains happy. It bloody won’t though I can feel it!
Think positive thoughts and all will be well. Maybe offer up a prayer to the god of the infernal combustion engine.
Good luck and let us know how you get on.
D