Golf GTi CO level too high - MoT failed, can you help??
Discussion
Despite failing to pick up two split flexi brake hoses, my local MoT station recently took pleasure in failing my Mk2 on excessive CO emmisions (about 7%)... I borrowed a mates gas analyser to confirm their reading. HC levels are about 250 to 300 PPM.
In total I have done the following:
- De-coked bores and flushed injectors.
- Changed oil and filter.
- Replaced plugs, leads, dizzy cap and rotor arm.
- cleaned air filter.
- adjusted CO grub screw (with little/no effect on emmissions)
- ECU was renewed a few years ago (standard map).
It seems to run absolutely perfectly, infact better than ever.
Local Golf breakers sells few air meters so not sure whether this may be playing up...
Does anybody have any ideas why these emissions are so high..?? I need to re-launch my wheels and reduce dependancy on the National (incontinence) Express.
Also, can anybody tell me what the black, plastic sensor is connected to the front left side of the engine block? The wire has a copper sheath which has broken. Not sure whether this sheath forms part of one of the core wires. Could this be connected to the emissions?
Cheers all.
In total I have done the following:
- De-coked bores and flushed injectors.
- Changed oil and filter.
- Replaced plugs, leads, dizzy cap and rotor arm.
- cleaned air filter.
- adjusted CO grub screw (with little/no effect on emmissions)
- ECU was renewed a few years ago (standard map).
It seems to run absolutely perfectly, infact better than ever.
Local Golf breakers sells few air meters so not sure whether this may be playing up...
Does anybody have any ideas why these emissions are so high..?? I need to re-launch my wheels and reduce dependancy on the National (incontinence) Express.
Also, can anybody tell me what the black, plastic sensor is connected to the front left side of the engine block? The wire has a copper sheath which has broken. Not sure whether this sheath forms part of one of the core wires. Could this be connected to the emissions?
Cheers all.
High CO means incomplete combustion which generally means it's running rich. I have no idea what that sensor is, but it might possibly be a coolant temp sender, and a faulty one of them would cause the engine to run rich. There are loads of other faults that could cause that, of course.
The sensor youre referring to is the Knock sensor and they generally lose most of their cable sheathing for some reason.
Shouldnt make any difference to your high co% reading though.
When did you last check the ignition timing and cam timing? Either of those can make a high co reading as well as the afm co screw not being correctly adjusted.
Editted to add- the coolant temp sensor is on the head at the front of the car and it is colour coded BLUE. There may also be a white sensor next to it or a blank.
hth.
>> Edited by deltafox on Monday 29th May 22:52
Shouldnt make any difference to your high co% reading though.
When did you last check the ignition timing and cam timing? Either of those can make a high co reading as well as the afm co screw not being correctly adjusted.
Editted to add- the coolant temp sensor is on the head at the front of the car and it is colour coded BLUE. There may also be a white sensor next to it or a blank.
hth.
>> Edited by deltafox on Monday 29th May 22:52
My '91 Mk2 Gti failed its french MOT with exactly the same fault late last year, albeit only at about 3% CO. As I didn't have access to a gas analyser I got a tune-up garage to check it out. They just cleaned up the whole air inlet system and screwed the mixture down at the Digifant airflow meter. It got the car through the MOT but it was clearly running lean (jerky at steady throttle, white deposits on plug tips) after their delicate work, so I've since richened up the mixture by 3/4s of a turn anti-clockwise on the adjustment screw.
It sounds like you've done all the obvious things to no avail. Some ideas - the Haynes manual gives some very simple electrical resistance measurements to check out the airflow meter - that would be a good start. Also worth spraying carb or injection system cleaner into the airflow meter while the engine is revving to wash any crap off the air flow measurement wire and the inside of throttle body. Bunging a hefty dose of fuel system cleaner in the tank while the petrol level is low might help if any your injectors are gummed up - I've done it but am not sure if it does a whole hell of a lot.
Haynes also gives simple electrical tests to verify that the knock sensor is working correctly - if it isn't then it affects the ignition advance so could be an issue for the CO level I guess.
Other than that I can only suggest a basic ignition timing check - cam timing shouldn't really be out unless the belt was changed and the timing cocked up since the last MOT.
Best of luck and let us know how you get on.
It sounds like you've done all the obvious things to no avail. Some ideas - the Haynes manual gives some very simple electrical resistance measurements to check out the airflow meter - that would be a good start. Also worth spraying carb or injection system cleaner into the airflow meter while the engine is revving to wash any crap off the air flow measurement wire and the inside of throttle body. Bunging a hefty dose of fuel system cleaner in the tank while the petrol level is low might help if any your injectors are gummed up - I've done it but am not sure if it does a whole hell of a lot.
Haynes also gives simple electrical tests to verify that the knock sensor is working correctly - if it isn't then it affects the ignition advance so could be an issue for the CO level I guess.
Other than that I can only suggest a basic ignition timing check - cam timing shouldn't really be out unless the belt was changed and the timing cocked up since the last MOT.
Best of luck and let us know how you get on.
wildoliver said:
Probably just a placebo though like redex
You're may be right about the Redex placebo effect - it always used to make me feel like I'd improved things by pouring it straight into the mouthes of carbs while revving the engine - all that white smoke made it look most impressive. I have no idea if it did any good whatsoever!
Cheers all. It has gone back into the MoT garage today. I haven't had a chance to make any changes but wanted to take advantage of the free retest! Plus, I have sorted brakes so would like to know that it is only the emmissions now holding me back.
I had a thought earlier about the ignition timing... When I replaced the rotor arm I did notice that the old one was seriously worn, one edge had pretty much erroded flat. The timing may have been set to compensate for with this wear, therefore the new arm may have thrown timing out...
My mate decided to rub my nose in it by putting the gas analyser on his Mk3. CO emissions went into negative figures, dos that mean Gordon Brown should be paying him to drive?!
I had a thought earlier about the ignition timing... When I replaced the rotor arm I did notice that the old one was seriously worn, one edge had pretty much erroded flat. The timing may have been set to compensate for with this wear, therefore the new arm may have thrown timing out...
My mate decided to rub my nose in it by putting the gas analyser on his Mk3. CO emissions went into negative figures, dos that mean Gordon Brown should be paying him to drive?!
The AFM was a used unit from Volksmania. When you say recalibrate are you refering to the CO adjustment?
To be honest, I just did a direct swap as had made the assumption that it had been used successfully before. Emissions down from 7.5% to 2.4%. MOT passed, job done (until next time).
To be honest, I just did a direct swap as had made the assumption that it had been used successfully before. Emissions down from 7.5% to 2.4%. MOT passed, job done (until next time).
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