TF Emissions failure - Forums
LinkBack Thread Tools Rate Thread Display Modes
post #1 of 10 (permalink) Old 01-02-2017, 09:57 Thread Starter
Registered User
Join Date: Feb 2017
Location: Finland Oulu
Car: MG TF
Posts: 4
Unhappy TF Emissions failure

Hi ! I'm new happy owner of MGTF 135 (10/2003, Royal blue/beige leather, chrome details) in Finland. Car didn't pass the emission test. On idle HC ppm is too high. Result:
On Idle
CO% 0.1 ok
CO2% 15.1 ok
HC ppm 235 NOT OK

On higher rpm
CO% 0.1 Ok
CO2% 15.3 Ok
HC ppm 77 Ok

Sparkplugs changed but check them again – one is still black and littlebit wet and others are ok. I haven’t seen any visible coolant leaks outside the engine. No coolant smell. Temperature is normal. Car goes well. On idle only a little petrol smell from exhaust. Engine yellow warning light is on. OPD failure code P0170. Has Anyone had same kind of problem ? Fuel injector fail, coils/leads or HGF ?
Emzii is offline  
Sponsored Links
post #2 of 10 (permalink) Old 01-02-2017, 10:28
Join Date: Mar 2013
Location: Helensburgh
Car: MG TF
Posts: 464
I don't know the codes but I had a similar problem last year and my IACV was the problem. I also needed to reset the throttle.

I took the IACV off and cleaned it of the sooty deposits. I used brake cleaner with no ill effect.

The engine should idle steadily at around 800rpm. I reset my throttle. To do this, I warned the car up to operating temperature. I switched off then switched on to position 2 on the ignition (did not start the car) I pressed the accelerator 6 times in 30 seconds, waited 15 seconds and turned ignition off. The car had been idling erratically at around 1100 revs with some hunting. After the reset, the car is steady at 800 rpm or thereabouts.
Dickybeau is offline  
post #3 of 10 (permalink) Old 01-02-2017, 10:56
Registered User
Join Date: Jul 2012
Location: Hunstanton
Car: MGF
Posts: 3,276
you have probably highlighted all the things to check in your post.. but...think on this... its a clue..:

1. unburnt fuel means its not being burnt.. its reaching the cylinder, not burning completely or at all, then being pushed out into the exhaust.

2. has the engine warning light come on? if not...the ecu isnt registering a fault from sensors , neither is it having a problem setting up the air fuel mix,
so i would use an obd reader to see if it could tell me of any faults that the ecu isnt flagging. you have a fault code-p0170

i would expect that unburnt fuel in the exhaust. to mess up the oxy sensor function.. and it will naff up the catalytic convertor. so not to see an ecu fault code displayed by it turning the engine warning light on, means that the ecu is still able to keep the air fuel mix ratio in range... thats tells one the ecu cant see a fault.. yet.

3. if there are no fault codes and the car " appears" to run ok.. then something that the ecu cant see, and cant indicate --- is happening... what might that be?

the ecu is trying to set the mix, its still doing that within its operating range, the oxy sensor isnt going out of range, the injectors, cam and valve control isnt flagging fault to the ecu...


4. its something after all the sensors?

spark plug not firing, even though the ecu is telling it to and cant see any prior ignition faults - that could be caused by a duff ignition circuit.. ie no high voltage generation, duff lead, shorted lead, duff plug.. all of those are after the ecu sensing..

i would check the whole ignition circuit, its connectors, supply, the coils, the leads, the plugs...

5.valve not closing properly.. not every time... but some of the time.. before the fuel has burnt... that could be difficult to investigate, because one might not see it with a static compression test, if it only happens at certain revs or at certain times..

6. valve not opening properly...not every time... but some of the time.. before the required amount of air for the fuel being delivered is the right mix.. an air intake valve problem..

7. - 5 and 6 are not common problems.. and usually are indicated by odd engine noises, and bad running, and idling.. even tapping noises on a regular basis if the timing starts to go way off... 5 and 6 are bad news, because the ecu cant see those faults.

your fault is more likely to be an electrical ignition fault, than a mechanical one.. given that you know the condition of the engine isnt far out.. just not meeting the spec..

and just one plug, being black and wet, not all four,,, is giving you a pointer which part of the ignition to look at.

8. if you are absolutely sure, that the ignition circuits are A1, but still get one black and wet plug.. it could be a cylinder problem, and you are getting oil into that cylinder, that is stopping the plug firing and contaminating the mix. i hope its not

as an aside.. a duff iacv will affect all four cylinders.. not just one. and the mix ratio wont be able to be set by the ecu, which should flag a fault... i.e it cant set the iacv.. it tries to.. but the mix stays wrong, and goes out of range..

you get a p0170 fault code because the oxy sensor is being contaminated by unburnt fuel.. and you have one wet plug not four wet plugs...... thats where the fault is. not the oxy(lambda) sensor...not the iacv... but the plug not firing.

9. if you clear the faulty plug ignition problem and are absolutely sure all four plugs burn the fuel properly, but still get a p0170 fault code.... then maybe the lambda sensor has gone awol...fried itself.. because if the air fuel mix is good, the lambda should burn of the contaminants, the exhaust should clear them out... and a good run should mean the car will pass its emission test..


Last edited by Incony; 01-02-2017 at 11:48.
Incony is offline  
post #4 of 10 (permalink) Old 01-02-2017, 11:36 Thread Starter
Registered User
Join Date: Feb 2017
Location: Finland Oulu
Car: MG TF
Posts: 4
Thank you for the quickly answers. Yes
- only one spark plug is black
- yellow engine lamp is on
- problem seems to be only on idle speed

First I'll check the spark plug leads (if problem is in coil, 2 plugs should be black, is that correct ?)
Emzii is offline  
post #5 of 10 (permalink) Old 01-02-2017, 11:52 Thread Starter
Registered User
Join Date: Feb 2017
Location: Finland Oulu
Car: MG TF
Posts: 4
Thanks for the quickly answers. Yes:
- yellow engine warning light is on
- only one spark plug is black
- problem seems to be only on idle rpm

First I'll check spark plug leads. If the problem would be in coil, two spark plugs should be black, is that correct ?
Emzii is offline  
post #6 of 10 (permalink) Old 01-02-2017, 14:28
Registered User
Join Date: May 2004
Location: Under a car near scunthorpe
Car: Maestros, 200, 600, ZTT
Posts: 25,281
Send a message via MSN to E_T_V
High HC's are because of unburnt fuel. Probably as a result of a misfire. Changing the spark plugs is a good first plan. Next would be to change the HT leads. If you know which cylinder is affected (one of the spark plugs looks different to the others), then swap the components about to see if the fault moves. Then you know which component is faulty. The fault code is probably because of the misfire but could also be a leaky injector too. (those can be swapped to see if the fault moves too - or tested and fixed if they are obviously dribbling)
E_T_V is offline  
post #7 of 10 (permalink) Old 15-02-2017, 18:20 Thread Starter
Registered User
Join Date: Feb 2017
Location: Finland Oulu
Car: MG TF
Posts: 4
Both coils, all HT leads and spark plugs changed. Fault code P0170 reset and it is not yet coming back (I bought cheap, 49€; OPD reader, works fine ). But 1 plug is still getting black on idle rpm. And when engine is warm idle is not completely stable.

Next I will change one fuel injector. If it doesn't help - then I'll remove cylinder head or has anyone other suggestions ?
Emzii is offline  
post #8 of 10 (permalink) Old 15-02-2017, 19:32
Woof Woof
Join Date: Aug 2010
Location: Nottingham
Car: TF160 Disco 3.9 XR4i 4trak Yamaha XV535
Posts: 10,703
You could just swap the injectors round to see if the problem moves to another cylinder. A compression test could be a good idea before pulling the head off.
barkingdog is offline  
post #9 of 10 (permalink) Old 15-02-2017, 20:46
Registered User
Join Date: Jul 2012
Location: Hunstanton
Car: MGF
Posts: 3,276
dont touch the head yet... you need to be sure its not an air or compression related problem. i go with what barkingdog says... if the injector isnt shutting off properly - you get excess fuel..., if its a "sticky" or a not seating properly valve... the compression will be low.. and a god forbid that its a ring or the head gasket.

it could also be residue in the cylinder that you have now cured by sorting the electrics...

i think you need to warm the engine, and take it for a spin to the redline.. then let it rest on idle for a few minutes and have another look... make the engine do some work..

it still might be that the oxy sensor isnt giving the ecu good readings because of the contamination in the down pipe... so i would want to be sure i had got rid of old carbon from unburnt fuel..

if after all that, one plug is still being contaminated.... then its water or oil getting into the cylinder...

but.. i think if that happens the ecu will see it.. via the oxy sensor... and flag a fault code still..?
Incony is offline  
post #10 of 10 (permalink) Old 16-02-2017, 00:31
Registered User
Join Date: Dec 2006
Location: Ashington, Northumberland
Car: MGTF 160, TF LE500, Nissan Leaf, KTM 990, Kangoo Van, Freelander 2.
Posts: 33,074
My guess would be an oil leak, possibly a valve stem.

Everything else has been replace and you aren't showing any errors, therefore it must be a system outside of the ignition system.

Oil in the cylinder would increase HCs too.
CJJ is offline  


Quick Reply

Register Now

In order to be able to post messages on the Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes Rate This Thread
Linear Mode Linear Mode
Rate This Thread:

Similar Threads
Thread Thread Starter Forum Replies Last Post
Emissions failure HELP! Muttsnuts MGF and MGTF (Sponsored by MGFnTFBITZ) 5 23-04-2010 20:47
emissions failure again... mitsirfishi MG ZR / Rover 25, 200 & Streetwise 13 29-09-2009 22:17
Emissions failure jetski MG ZR / Rover 25, 200 & Streetwise 0 15-01-2008 18:22
emissions failure fletty100 MG ZR / Rover 25, 200 & Streetwise 0 21-10-2007 13:28
Emissions Failure Nick Curtis MG ZR / Rover 25, 200 & Streetwise 4 18-10-2006 18:42

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome