964enthus

Hi
over the last 7 years ,i had always had excellent test results :
HC 4 to 12
Co 0.008 to 0.132
Sudenly ,this year :
HC 130
CO 3.23 !! (nb 3.5 is the limit )
I thought the o2 sensor might be disconnected :apparently not
i tested the O2 sensor with a voltmeter ,the readings are ok
the car behaves just the same as before ,no smoke at the exhaust ,no stalling ,acceleration the same ,no misfire....
i am puzzled ,because if CO increases just a bit ,the car will not pass the test next year
Would you have any ideas about where this could originate from / ? what I should look at ?
Already had similar issue ?
All suggestions welcome
peter

Steve Weiner-Rennsport Systems

Peter,

One needs a LOT more detailed information in order to offer anything constructive.

This would include:

Total miles on engine
Mileage on distributor caps, rotors, plugs, ignition wires
Air cleaner condition & mileage
Oil consumption
Oxysensor mileage

964enthus

Dear Steve
thanks for your questions
mileage is 68 000 miles
all equipment is original

Mileage on distributor caps, rotors, plugs, ignition wires
ALL BUT PLUGS ORIGINAL /PLUGS 500 MILES
Air cleaner condition & mileage
CLEAN 3000 MILES
Oil consumption
HARDLY ANY /NB I ONCE HAD A CLOUD OF SMOKE AFTER A 2 months stay in the garage /PROBABLY SLIGHT OVERFILL / DID NOT REHAPPEN AFTER REMOVING HALF LITER OF OIL
Oxysensor mileage
ORIGINAL ,VOLTAGE TEST SHOWS OK
peter

hamah

Could be an anomaly in the test or equipment itself. Did you ask for a 2nd test on different equipment?

964enthus

yes in fact the first test was at the mot itself
3 weeks ago
i thought it was simply a problem of disconnected o2 sensor
so ,i checked the connection and had another test at another garage today

Steve Weiner-Rennsport Systems

Hi Peter,

Thank you kindly for the data; that really helps.

At 68K, everything is long past due for replacement as those items determine ignition quality and combustion. I would install new caps, rotors, plug wires, and perhaps the oxysensor, depending on how fast its cycling. If you can read the values on the DVM, its toast. A fresh one cycles so quickly that the lambda numbers are almost unreadable.

lateforlunch

^all great advice. In addition I think you'd be wise to check for vacuum leaks and/or a leaky fuel pressure regulator. Dumping un metered fuel into the intake will throw off your CO just as easy.

swftiii

When was the last oil change? I had an issue once when the car had sat for a while and the oil was pushing a year. Changed the oil and put a 100 or so miles on the car and passed the next try.

Good luck!

axl911

Your HC also jumped 10x to 130! You're running rich! Is this at idle or at load?

Could be that you have a vacuum leak.

964enthus

many thanks for all your comments and suggestions
oil change : was done last year (only 500 miles)
idle or at load test ? at load :2500 rpm
such a sudden change seems to indicate an excessively rich mixture
I'll try first : vacuum leaks and/or a leaky fuel pressure regulator(my job for tomorrow !)
Am I right to suppose that running the engine with that sort of emissions WILL NOT DAMAGE THE CAT ?