MOT failure - help!

[Mike16v 10]

So my 16v failed its MOT on emissions. The CO reading was 5% at idle and 6% at fast idle. As I understand it, the reading needs to be below 0.3% - so it's not as if it's even close. Since it passed with no problems last year, it looks like something I've done...

 

Ive replaced the dizzy cap, rotor arm, HT leads and plugs on the ignition side of things. I fitted new injectors a couple of weeks ago (thinking the old original ones were coming up to 100k miles so were probably not at their best.

 

The cat and O2 sensor were replaced 2 years ago.

 

The garage who did the MOT were mostly clueless, but did say they adjusted the screw on the metering head and managed to get the idle CO down to 0.2%. As soon as the throttle is touched it shoots right up to 6%+

 

Anyone had a similar problem? I'm wondering if the new new injectors are duff or does it just need setting up correctly?

[Harrier 1]

Where did you get your cat from ?

some of the things on sale from the motor factors are really pants and you can be lucky if they last 12 mnths

[Mike16v 10]

That's a good point it wasn't expensive if I remember. It's probably only done 500 miles since it was fitted though.

 

Trouble is, I can't find a decent garage near me who understands the fuel injection. They see the metering head and just glaze over.

[Portent 0]

I see you may be in Kent? You could maybe try giving SE Autoworks in Guildford a call. I take my car there and while I've only used them for fairly general stuff they seem to specialise in VW's and often have older cars there such as Corrado's. If you're in Kent it's not a million miles away; maybe an hour. Perhaps call them and sound them out on what they would be able to check. I've always been happy with them and they seem to know their way around Corrado's.

 

EDIT: Are 16v and VR6 cats the same? I have a spare VR6 one you may be able to borrow temporarily to at least check if that's the issue.

 

EDIT 2: Would engine codes show a defective O2 sensor?

Edited June 26, 2015 by Portent

[Mike16v 10]

Thanks Portent, I may give them a call. Most garages near me haven't got a clue about it.

 

I may change the cat as it's not too expensive. The type approved ones seem to be going for around £80-£100.

 

Re the engine codes - it's a '93 car and I was under the impression that I would only get ABS codes from it. You think I might get something more useful?

[Mike16v 10]

Had a thought about this last night...

 

I unplugged the 5th injector and measured the voltage to it on startup and got 12v.

 

I waited until the engine warmed up and expected to see the voltage drop or disappear. It didn't drop at all apart for a couple of split second blips down to 5v. But with the coolant temperature at 90C there was still 12v at the injector.

 

Am I right expecting the voltage to drop once the car is warmed up?

[davidwort 0]

oh, no, another garage messes with the factory calibrated settings on the metering head trying to compensate for another issue they couldn't find.

CAT change won't fix your CO problem, a 1.8 16v with no CAT will be way ower than that on idle CO, there's something fundamentally wrong with the fuelling or the engine itself, is it burning oil badly?, what do the plugs look like, pretty black 'd imagine.

You really need to find a bosch injection specialist, the system is very close to that used on fords and porsches, Volvos and more so someone near you must be able to help.

I'd look at testing/replacing coolant sensors, cheap and easy and often the cause of overfuelling probs.

[Mike16v 10]

So ran it up to the garage with the 5th injector unplugged.

 

Emissions are better - its perfect on idle but still goes up to 4% CO on fast idle (as opposed to 6% before). They seem to think the lambda sensor has gone wonky so going to try a new one.

 

The car starts fine in this weather without the 5th injector and the car only comes out in the summer, but I'd like to find out why its operating all the time. I'm assuming it's controlled by the ECU which is getting temperature information from the coolant temperature sensor?

[corrado wannabe 12]

Mike,

 

Check the wiring on the car side of the block connectors for the lambda (oxygen) sensor.

 

It has been posted many times on here not to go and buy a lambda before checking the wiring first.

 

If only I had taken heed on this advice before I had done just that. I replaced my lambda sensor to find that the wires were broken off from the connector on the loom side.

 

Worth a look before you go and spend the dosh.

 

If you do need a lambda sensor I just bought one of these genuine ones:

 

http://www.ebay.co.uk/itm/VW-G60-Lambda-02-Sensor-Genuine-037906265B-/161599669938?pt=LH_DefaultDomain_3&hash=item25a01746b2

 

Dougie

[easypops 8]

I had the same problem with the 5th injector on my old valver, I unplugged it and left it that way for about 5 years, through winters as well and it always started fine, passed all MOT's that way too

[sankysvr6 0]

This might help

 

http://www.clubgti.com/showthread.php?195423-HOW-TO-Check-repair-and-tune-your-MK2-Corrado-1-8-16v

[g0ldf1ng3r 15]

This might help

 

http://www.clubgti.com/showthread.php?195423-HOW-TO-Check-repair-and-tune-your-MK2-Corrado-1-8-16v

 

favourite - thanks sanky

[Mike16v 10]

Decided to have a look at the lambda sensor wiring yesterday and change the engine mount while I was at it. The wiring looks in good condition. While I had the air intake off from the air box to the throttle, I noticed that the vac hoses which connect to the little valve in the air intake hose were the wrong way round. Can anyone shed any light on what the little valve does or if this will make any difference?

[Knuckleduster 10]

Hi Mike, Had the same trouble with the lads A4 last year at MOT time. Cat had been replaced 3 years ago and had just scraped through emmisions before, but last year it gave very similar results to yours. After a lot of work and several visits to the MOT station it turned out to be the CAT that was fitted by a garage that my lad had taken his car to. I had changed and checked everything and in despiration got a TYPE approved CAT which cured the problem. When I took the "old" one off I spotted the problem straight away. The cat fitted was a two sensor one with one of the sensor holes blanked off with a bolt. The correct one has one sensor and costs more to buy. Thinking about it the 2 sensor type has less material in the cat to get the emmissions down, relying in the ECU to alter the mixture on a faster cycle. Pre and post cat sensors cause the ECU to cycle the mixture far faster than the single type hence the high CO readings. Got rid of the A4 after it broke a drive shaft at the pinion. Replaced it with a Corrado VR6--more fun!!

[Mike16v 10]

Thanks Knuckleduster, I checked the cat a few days ago because I didn't fit it myself. It is the one sensor type.

 

The MOT tester managed to make it pass although I think he's done some sort of slight of hand rather than sorting the job properly.

 

I've bought a new 02 sensor although I haven't had time to fit it yet.

 

When I've put it on, I'll check the emissions again. The car is actually running fine, although it doing an average 16MPG which is a bit scary and the exhaust still smells of fuel.

 

Fingers crossed the sensor will sort it - if not I'll do as you suggest and go for another (type approved) cat.