Question about 1998 Audi A4

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Hi, Few days ago my Audi A4 1998, 128K done, failed MOT on high CO emissions. Somebody suggested to put Injector cleaner in fuel, and smoke free in Engine, did that, went for a spin night before and then took it for retest in the afternoon, it failed again, However the readings were slightly lower. Fail readings were: first idle test: 2558 rpm CO--limit (0.30%) reading 0.48% Second idle test:2527 rpm CO--limit (0.30%) reading 0.53% Day 2. first idle test:2720 rpm CO--limit (0.30%) reading 0.51% Second idle test:2549 rpm CO--limit (0.30%) reading 0.46% Spoke to a local garage guy, he checked that Oxygen sensor is working and needs to replace the CAT. I am not convinced, as the car runs absolutely ok, no lights fron ECU etc.. Please advice?? thanks

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Replace cat. The mechanic was correct.

Posted on May 16, 2011


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After warm up engine runs ruff and loss of power

Injectors need cleaning if it is a diesel
There is a buold up of contaminants in your fuel system that needs to be cleaned out

If it is a petrol engine I would be very surprised

Just add a couple of treatments of injector cleaner to a full tank of fuel and go out for a high rev blast for an horor twom that should hopefully clean it.

My old renault laguna failed emissions so I PUT 2 bottles of forte injection cleaner and went out for a 70 mile blast, it was a diesel car. I returned to the testing station within 2 hours and the black smoke had ccleard and I got the pass certificate.

Jul 09, 2015 | Cars & Trucks

1 Answer

High CO emissions. MOT failure. No codes. Runs like a dream. Fuel consumption high

check that the cat converter is not failing and blocking up the exhaust system. or not doing it,s job. replace both HO2S and O2 sensors

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1 Answer

Hi Audi A4 1.8 T sport, X reg failed mot on high emissions Front Lambda replaced, and readings still high (running rich) any ideas please

hi this could be a few things but more than likely it is either the MAF sensor or MAP sensor, these things do roughly the same thing, but the MAP also adjusts the timing through the ECM , either one would cause this to "over fuel" and not burn correctly, the starting place would be try the MAF first as this is the common one, make sure spark plugs have been changed as this also will help, if you still get a fail, then try the MAP sensor...hope this helps good luck..

Sep 17, 2010 | 2000 Audi A4

1 Answer

99 audi a4 1.9 td red i starts perfect but has a misfire when cold and wont rev over 3000 revs and puts out a bluish white smoke but if i bring it for small drive turn it off for few mins and start it...

first check your glow plugs that they are not faulty,if faulty replace them,then get a bottle of injector cleaner and put it in your fuel take and replace your diesel filter,and also change your oil and oil filter,maybe your hydralic lifters are not preasurising when cold

Nov 19, 2009 | 1997 Audi A4

2 Answers

Hi, 2000 Landrover Freelander 1.8 petrol, failed MOT on CO emissi

check both lambda sensors for breaks in wires and for open circuit on heater side of lambda sensor on the one under the car on the second cat,failed heater element will not heat gas engough for sensor to read causing false readings , also check for slow i.a.c valve on inlet manifold.

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2 Answers

Improper fuel combustion; need to pass emissions test

Sounds like you need to replace your oxygen sensors.  If you have a four cylinder I think you only have one oxygen sensor and the six cylinder I know has 2.  You can check that out at your local parts store.  Anyway, the oxygen sensor helps the computers in your car make sure that you are getting the correct amount of fuel and air during combustion thus controlling your emissions.  I would think that if you haven't replace these in a while that is what is probably keeping you from passing your test.  Change the oxygen sensors and put a bottle of good fuel injector cleaner in a full tank of gas and you should be good to go.  I would suggest Greased Lightening fuel injector cleaner that can be purchased at Napa and O'Reilley Auto Parts.  Let me know if you have any other questions.  Thanks for an honest rating and for using FixYa!

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2 Answers

Ford failed MOT on High CO emission

High CO usualy means the O2 sensors are not reading properly. Take it to a parts store that can read codes, I know Auto Zone does in my area. If it is the O2 sensor it is an easy fix but the sensors run about $50.00 each.

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It sounds like the catalytic converter is bad.

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1 Answer



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2 Answers

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make sure to smell the oil and see if it is contaminated with fuel
if it is then do an oil change and try to re test

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