Failed emissions test

"Signal" > wrote in message
...
>I would appreciate any comments from readers here on this, I wasn't
> prepared for this and don't know where I stand....
>
> My beloved Golf '96 1.8 Mk III SE - failed on emissions. The cat has
> been progressively producing a stronger and stronger odour in recent
> times. The car pinks on regular unleaded when the engine is turning
> 3000+rpm - this goes away with higher octane fuel. [Pinking went on
> for some time unnoticed.] Fuel economy has dipped by ~10%. The car is
> due for service; spark plugs, oil, oil filter etc are all due for
> replacement. The engineer feels the problem relates to the valves and
> is may try a compression test tomorrow, if so, and depending on what
> happens there may look under the head. (Head gasket?) He said if I'm
> lucky it could be a plug, but I should be prepared for worse. He did
> try to explain possible outcomes, but unfortunately it was
> gobbledegook to me and flew right over my head. Can anybody comment on
> causes for these symptoms, anything else I should consider? I tend to
> trust the mechanic.. should get a second opinion/quote anyway?

Might help if you posted the details of the test. Did it fail on HC, NOx,
or CO?

Pinging can be caused by too much compression (carbon buildup) and/or bad
ignition timing. But post up the results of the test in more detail...that
may help.

The general tuneup also is a good idea...don't bother emissions testing a
car that you know is overdue for service...do the service first, then test.

> Yes of course... I didn't have the documentation when I posted. It is
> the CO emissions on which the car failed. Here are the results :

> DESC LIMIT READING FAIL

> ENGINE TEMP MIN 80 82

> FAST IDLE :
> ENGINE SPEED 2450-2850 2720
> CO MAX 0.30% 0.54% X
> HC MAX 200PPM 32PPM
> LAMBDA 0.97-1.03 0.98

> SECOND IDLE TEST :
> ENGINE SPEED 2450-2850 2720
> CO MAX 0.30% 0.57% X
> HC MAX 200PPM 41PPM
> LAMBDA 0.97-1.03 0.98

> NATURAL IDLE TEST:
> ENGINE SPEED 650-950 943
> CO MAX 0.5% 0.05%


> Which is a very stupid mistake I made!!

> So the mechanic ran a compression test and the 4th cylinder was 6%
> down. He suggests this was allowing fuel to leak past the piston and
> on into the cat, and that is what caused the very bad smells. [I hope
> I am repeating this correctly]. The spark plugs where changed, oil
> topped up, timing checked (reset?) - the 4th cylinder is now at 100%
> and holding 175 PSI - so the MOT was passed. He then gave the car a
> road test and was satisfied it was performing OK for now, but noted
> the idling wasn't as good as he would like - and that I should monitor
> the cars performance and return if the problem reoccurs.

> Here are the post results :


> DESC LIMIT READING FAIL

> ENGINE TEMP temp gauge showed 'warm'

> FAST IDLE :
> ENGINE SPEED 2500-3000 2905
> CO MAX 0.20% 0.02%
> HC MAX 200PPM 24PPM
> LAMBDA 0.97-1.03 1.00

> NATURAL IDLE TEST:
> ENGINE SPEED 450-1500 907
> CO MAX 0.3% 0.04%


Blah, blah... Okay, look:

CO is a measure of how rich or lean your mixture is. Period. I can't
see why someone would measure both CO and Lambda and I can't imagine
what equipment you are using that does both, since CO is usually derived
from lambda. That said, .98 means you running slightly rich, very very
slightly. Still quite reasonable. Those CO numbers do not correlate
to a lambda of .98 (especially post cat).

There is no legitamite way to restore compression to the #4 cylinder
without removing the engine or at least cylinder head. So basically,
I'm just not buying any of this. Adjusting the timing and replacing the
spark plugs would have absolutely zero impact on compression. "Topping
off the oil" I suppose might if your cylinder is leaking you might be
getting a little extra sealing from the oil, but if that were the case
your compression would be higher than the others. 6% low is not good, but
its not outrageously bad, its probably still within spec.

Your first "fast idle" test shows a maximum CO of .3%, the next one has
a max of .2%. Say what? Your HC levels which should be roughly proportional
to the CO levels (at a minimum) dropped by 50%, despite your CO levels dropping
2600%.

Either someone is feeding you a load of crap, or you're feeding us a
load of it. Either way, I'm calling shennanigans...