Failed Co2 emissions

[maxmc2]

HI Guys

MOT failure on my MK3 golf GTI 8v

Needed to replace back box which i did and still the Co2 emissions are high.

Took to the garage today for some diagnostics and report as follows.

No air leaks in the exhaust.

Co2 emissions at rest are fine, but when you rev to the required 2500rpm the Co2's shoot high making the car run rich. He was baffled. Took up a spare Maf sensor i had lying around which i know is fine but still no joy.

The car has had a new cat, downpipe, cam belt and back box.

Mechanic said he could spend hours replacing parts costing me a small fortune but has suggest i trail the net to search for clues as to what it could be.

Any ideas guys need to get the car back on the road.

Thanks

[Screech16v]

lambda sensor? ,have you had it plugged in to check for dtc's

[maxmc2]

lambda sensor? ,have you had it plugged in to check for dtc's

Well it had a new lambda when the cat was fitted about 2000 miles ago, i asked the mechanic about that and he didnt seem to think it a problem as the lambda readings were within range... and no haven't checked for codes yet

[tshirt2k]

You must mean CO? Check for a duff coolant sensor or similar as these would cause rich running

[maxmc2]

You must mean CO? Check for a duff coolant sensor or similar as these would cause rich running

Yeah the CO sorry.

Have a new sensor that im going to fit now.

Is it also worth checking for vacuum leaks around the inlet?

Do mk3 golfs have EGRs?

[tshirt2k]

Change all vacuum lines for 3mm id silicone if you can. Vac leaks arent good either as its unmetered air.

[*tell*]

we fitted a new landa sensor to a mates vr and cleared all the codes.
a week later scanned again same code turns out the cheap landa sensor wasnt
up too the job?

[maxmc2]

OK

So last night i replaced the ECU temp sensor, new PCV and piping, cleaning the inlet manifold checked for leaks and run some injector cleaner through and gave it a good blast.

Apart from an overcooling issue to to air in the coolant system i think i have done everything i can to get the CO down.

The only other thing that i can think of is the timing is a tooth out, but then it wouldnt run as well as it does, or a dodgy ECU, any thoughts.

Started the car this morning and noticed there was an exhaust leak at one of the joints, the cars in for its re test today as its the last day for a free re test.

Would the blow cause any problems do you think? also the new back box i got could that causes the COs to go up.

Cheers for all you help guys.

[tshirt2k]

Exhaust leaks can cause problems but depends where it is. If the lambda sees a lean condition it will richen up the mixture.

[maxmc2]

Exhaust leaks can cause problems but depends where it is. If the lambda sees a lean condition it will richen up the mixture.

Its where the back box joins the middle box the joint isnt perfect and something i need to sort out but i need to get it taxed and MOT'd before i can do anything really, ive put some putty round it for the mo just hoping that doesnt cause it to fail again.

Grrrr