MOT Emissions

[Thommo]

Just failed my MOT dismally on emissions ☹️

 

Its an low mileage 2002 1.6K on standard exhaust/electronics but with DVA work to head/cams a few years ago.

 

Always sailed through before but way out this year (at usual test centre) ... took it away for a good blast with a dose of petrol additive but still no joy.

 

Anybody able to help on likely cause...I guess Cat and lambda sensors are most likely

 

 

[Jonathan Kay]

Are you sure that shouldn't be visual inspection only... or perhaps it was.

 

Jonathan

[shn7]

Think air leak on exhaust side can cause problems too. Post the readings and it might help those with more specific knowledge.

[shn7]

Not on a car of that age. Unless you "know a man who can"

[Thommo]

Sadly not just visual...tester is very helpfull and said he had looked through the guidelines for a loophole, but couldn't find one

 

Results are:

 

Fast idle 1:

CO 7.582

HC 388

Lambda 0.822

 

Fast idle 2:

CO 0.39

HC 256

Lambda 1.732

 

Natural idle:

CO 4.334

 

Second visit he said he got it down to 3, but thats still well over

 

[ACJ]

Just recently had a similar problem with emissions on an MOT. I think the numbers to pass are CO - 0.3% or below, HC 200ppm or below, Lambda - 0.9 to 1.03. The test checks all 3 on fast idle (2500 - 3000) and only CO at natural idle. Try to run as close to 3000 as this seemed to help for me.

 

I was lucky that the car I was working on had an emerald ECU allowing me to alter the fueling whilst connected to a gas analyser before going to the test. Looking at your figures I think you must have an exhaust air leak (as already posted) as Lambda is way too high at 1.7 Check all the joints for soot and seal with exhaust paste or sim. Also try spraying brake cleaner around the intake manifold whilst running to see if the idle changes as that would also point to an air leak. (go carefull as it is flamable!)

 

Although lamda is reading high (or weak mixture) the reading is taken at the exhaust exit so it's not a reflection on if the lambda sensor on the car is working correclty. This can be checked using a multimeter and measuring raw voltage, I will have to just check on some notes to remember which pins and the voltages you should use.

 

Last thing is I presume the car is very hot - not just warm, giving the cat a fair chance to work.

 

Be interested to hear how you get on

 

Andy

[peter clarke]

Have had a similar problem a few years ago with similar readings. Checked Lamba and it was no good, new one and then set up with gas analyser and all perfect ,below 0.2 reading

[Titanium7]

Just had the same problem with my 1.6 with a DVA K05 upgrade a few days before the MOT and running on a base map. Not that its much help to you but adjusting the fueling on the fitted Emerald it passed easily.

 

 

[charlie_pank]

One lambda reading is twice the other. That means for the same conditions you're putting in twice the fuel eg. 15 mpg or 30 mpg - huge difference!

 

There's clearly some sort of problem, my suggestions are:

 

- ECU thinks it's hotter or cooler than it is - perhaps a sensor is misreading or there's a bad contact with one. I'd start by checking the TPS voltages- IACV sticking causing air - leak. You can unbolt it and check it is resetting properly when you power up the ECU

- air leak somewhere on exhaust side (so ECU increases fuel input to compensate for what it thinks is leaning off)

- air leak on inlet side (less likely as ECU can increase fuel to correct lean mixture)

 

I don't know whether your ECU and lambda setup run in a feedback loop under MOT conditions or not, so difficult to say precisely what's wrong. What ECU are you running, are you able to connect to it and see what it thinks is going on?

 

[Thommo]

Thanks for the advice guys, had a good look at the exhaust and no sign of any leaks there, so looks like Saturday will be spent checking all the sensor outputs...standard EU3 ECU so sadly no quick fiddling on the laptop to get it through

 

Either that or find the friendly mot tester who should have gone to specsavers and gets his exhaust pipe's mixed up... 😬

[johnv]

where did you take it?

[Thommo]

At the moment it goes to Farnborough Car Care, up till this year they always let me sit in the car (being 6'4 I don't have a seat so the tester probably couldn't reach the pedals) and the owners son used to race karts/cars so we have a good chat about racing in general...I think they are as friendly/helpful as they can be, but they aren't particularly knowledgeable about 7's.

[johnv]

I took mine to Foster&Heanes in Hook after recommendations on here, and, whilst thorough on the safety side, they didn't seem too picky about the emissions.

[Thommo]

John, thanks for the tip, not far so may have my tinker then go there

[charlie_pank]

If your lambda readings are really varying that much, you really should find the root of the problem rather than a bent MOT tester. A Rover garage should be able to plug ino the diagnostics socket on the loom and tell you what's going on. I don't have a K any more so I can't remember where it is, someone else should be able to tell you.

 

Start with TPS voltage and checking/cleaning IACV if you don't find anything untoward, find a friendly Rover garage...

[Thommo]

Well, whilst waiting for a mate to borrow his mate's diagnostic code reader (still waiting) I checked the Lambda sensor outputs (ok), AICV seems to be resetting ok, no obvious leaks anywhere, not sure about checking TPS voltages but read about resetting by pumping throttle 5 times to reset it....

 

Desided to pop it into another local garage and...it passed

 

Tester did mention he struggled a bit with emissions (I hadn't said anything about problem when booking it in) becouse of difficulty getting it to hold constant revs for long enough (which I have also noticed getting noise tested in the past).

 

He suggested TPS maybe being the problem, anyone know if I can test this at home with my trusty multimeter, which wires/what readings I should be looking for

[ACJ]

Not sure if this will help as it may only apply to MBE system cars, worth a try though. The TPS will have 3 wires going to it. First thing is to figure out which is pos, neg and signal.

 

Disconnect the TPS Sensor and work on the TPS sensor plug – not the wiring harness plug.

 

Using a multimeter find the two wires which do not vary their resistance when you move the TPS spindle. These two wires are the +5v and GND - you just don't know which way round they are! To determine this connect either one of the +5v/GND pair to the remaining wire – which by default must be the signal wire. Note the resistance value you see and operate the TPS spindle.

 

If the resistance value INCREASES as you operate the pot then the wire you are working with is the GND

If the value of the resistance DECREASES as you operate the pot then the wire you are working with is the +5v

 

In theory if this process works the TPS should be working ok. However, if you want to check the signal being sent back to the ECU you will need to connect the sensor back to the loom and power up the ECU (only ignition, not running). Now test the voltage across the signal and pos pins, or signal and neg pins. It should vary between 0 and 5v on most systems (this is the part I am not 100% sure of on the standard MEMS unit).

 

It will require you to have a needle end on the multimeter lead to push up the back of the plug whilst connected.

 

Be really carefull not to cause a straight short - never done that and not sure if it would cause any damage but not worth risking it!

 

Hope this answers your question,

Andy