Help - MOT fail on HC emissions - now fixed!

My GTI has failed it's MOT for the first time in the 27yrs I have had it.

The emissions readings for CO2 were fine at 0.30,  but the HC reading was 1547ppm, and the limit is 1200. Last year passed fine well within limits IIRC.

Since last year just done 1500 miles and as background but don't know if relevant at all this is everything done to car.

-new oil pump, pressure relief valve went on old one causing excessive pressure- cleaned out crankcase breather gauze as precaution when new pump fitted.
-new HT leads fitted last weekend.
-new custom stainless exhaust fitted.
-old air box had lots of holes drilled in to increase induction noise, but after fitting new exhuast couldn't hear this anymore so covered all the holes up, so now just draws in air from the standard inlet pipe.

car was last used in September, and it has sat in garage until last weekend when I started it up, to be fair did smell a bit of fumes but thought it was because it was enclosed in garage.  As MOT had run out and not taxed , I wasn't able to give it much of a run to the MOT centre, just about 2 miles down the dual carriageway.

since getting the fail today, I did give it a slightly extended route back home and ran it as 5000rpm for couple of miles. I have done some searching on here, and so far checked/done-

- removed plugs and all same light brown colour, so thought this might rule out the HT leads being at fault?
-checked all the vacuum pipes for splits and tight joints.
-removed fuel meter head rubber cover and the metal flap inside seemed in okay condition, but gave good squirt of carb cleaner that I used last year when getting car out of it's long hibernation.

So, as I won't be able to check the readings until it goes for its next test on 9april as I don't have any equipment to test, what else can I do to up the chances of a pass. Realise the garage may do a few bits to try and get it down - they didn't today as it also has to go back for a new ball joint as failed on this also.

have read about the 5th injector - could the wiring just be disconnected to stop it working - realise would give some cold start issues possibly, but only use in summer months?

finally  - just to mention that has a Kent Cam fitted so never idles perfectly anyway, but garage did say engine seemed to be hunting a bit.

There we are then, sorry if it's a bit of a ramble but thought it might help the experts out there - plus remember I don't have much mechanical knowledge or tools to do some more in depth checks - do have a multi meter but no idea how to use it!
 

Sounds like a dodgy plug lead. Find by elimination.

paul_c said

Sounds like a dodgy plug lead. Find by elimination.

Would that make one of the plugs be a bit black and damp though, as they all look same? although I have only done a few miles.  I have all the old leads so can put them back on.
 

Looking at plugs is meaningless.

Could it just need an 'Italian Tune-up' Richard if it's been sat?

Although the CO is a pass it looks like it's running very lean to me. Not sure if that has a knock-on affect on HC though?

From memory the ideal CO is about 0.8-1.2

Just did a brief bit of googling and the lean mixture could be causing the high HC.

If I recall also internal oil leaks could cause high HC? But doubt that's an issue with yours esp. as plugs all OK.

I'd say take it for a spanking and get mixture looked at if still high on HC. What were the figures on last year's MOT?

Thanks for replies so far, I haven't got the figures from last year, sent MOT paperwork off for number plate change and the emissions print didn't come back.

Will defo put the old plug leads back on, it's a real pain that you are only legal to go to MOT station when the tax and MOT have run out, however I have a plan to accidentally miss the slip road on the dual carriage way and then it's an 8 mile round trip to get back!  

I know you will say what are the chances of getting stopped, but just this morning went a different way out of village and there sat a police car having pulled someone over - never seen one on that piece of road all year!.

Your high lift cam is not helping. What is your ignition timing set at?

dubboy said

Your high lift cam is not helping. What is your ignition timing set at?

Sorry no idea, all I know when it was fitted about 10k ago, they fitted an  adjustable vernier pulley to help set the timing??

As mentioned dont have last years MOT figures, but the one before that way back in 2000 has CO2 as 2.82 (but HC -as 92 which surely isn't right, but it is handwritten, not a print out ) so hoping that getting it moved from 0.30 up to something like 1.5 might be enough along with the old HT Leads- what do you think?

Unless you have the definite solution then  swap the cam back for a standard one. That should get it back to a pass and then you can do some better investigation once its taxed and MOT'd.

Also - how much fuel was in it over the winter? The fuel's not gone off has it?

I can't find the old CAM it was changed 18 yrs ago. Fuel was Superunleaded, put two gals in tank in sept, have just filled up though on way back from MOT.

Drive to Bert for mot save messing mate 
bert

What's the air filter like?

mark1gls said

What's the air filter like?

New last year so only 1500 miles, will check not got too dirty for any reason.

There is also a breather on top of the rocker cover which can get blocked, try removing the hose and using a bit of hose to blow down it (you won't be able to get your mouth around it where it is so that's why you need a bit hose) Take the filler cap off before you blow down the hose.

As long as you are driving to a pre-booked MOT, there is no restriction on how far you travel to get to it. A colleague of mine built a kit car in Surrey, and booked his MOT in Northampton - gave it a good blastup the M1
If you do get stopped on the way, the police can call the MOT station to check you have pre-booked - of course if the car has an obvious serious defect you can still get done for it, but then that could happen anytime, MOT or not.
Good luck
Lee

Thanks LeeO didn't know that, thought it had to be somewhere reasonable.

Yes, I don't think I would risk such a long blast, but you definitely don't have to pick your nearest MOT centre.

Check for air leaks on the inlet side. Mine failed on emissions and HC.

It had a leak on inlet manifold that made it idle rough, although ran fine when under way at higher revs. The air/fuel mixture was being upset and running far too lean on at least 1 cylinder.