My sons Pug 106 has failed the CO emissions on first fast idle at 0.57% volume and the second fast idle test at 0.95% vol.
The joint at the back box has the slightest of leaks, and the tester has told me that it may be drawing in air from this point and causing the problem, but what I don\'t understand is where the CO is coming from. He also advised me to put in some fuel cleaner to clean the single point injecter, combustion chambers and lambda sensor. Is this likley to work?
Reggie
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CO emissions are, I believe, related to incomplete combustion. I\'d suggest a check of fuel mixture issues. Air filter, injector settings, maybe cleaning but I don\'t have much faith in these products. Can\'t really see that the back box has anything to do with this except that CO is more likely to enter the car from the underside.
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CO (carbon monoxide) is indeed the result of incomplete combustion, which if complete would lead only to carbon dioxide (and water of course). This means either overfuelling or air starvation (e.g. blocked air filter). In a car with an ECU the lambda sensor should detect an imbalance and adjust accordingly.
Lambda is a numeric value indicating accuracy of combustion: exact balance has a value of 1.0, and the MoT test allows a small variation either side of that.
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Does this therefore sugest that the lambda sensor is possibly dirty and not reading accurately, and if so how do you clean it. The M.O.T. centre suggested the fuel cleaner and I've just had a quick look in the archives and a Micra that had this treatment with the same problem was cured! Also, I cannot understand the CO reading rise from 0.57% for the first test to 0.95% for the second test. Apparently a second test is only carried out if the first test fails.
The only other concern (except for the air filter which I will check tomorrow) was that I put a replacement aftermarket "cat" on the car about two months ago with a one year (fairly cheap) guarantee. Could this possibly have anything to do with it?
Thanks for your help.
Reggie
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How old is the car. We have had instances of incorrect ECU programming causing the mixture to go rich at precisely the point of fast idle testing. However in this instance I would suggest getting the operation of the Lambda sensor checked on an oscilloscope for voltage swing and frequency, If that checks out OK I would suspect the Cat. A professional injector cleaner (Forte, Protec, Wynns) would be beneficial if the operation of the sensor was marginal.
Andrew
Happiness is a T70 at full chat!
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The car is 1992 "K" reg. I have put a dose of Wynns in the fuel tank and will try and irradicate the minute leak before the back box and will take it for retest sometime next week, hoping that a cure has been effected.
If it fails again, can I presume that a half decent garage can check this "voltage swing and frequency", or do they just start fitting new parts until "the faulty one" gets replaced?
I do have a multimeter myself, but do not really understand the above. Is it easy to explain?
Thanks again.
Reggie
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The voltage should swing between 30mV and 800mV roughly at about 60-80 Hz. The voltage is measured on the black wire of the sensor. If you have a digital meter you should see a continuos variance in the voltage. If you have a graphing meter somuch the better but DONT use an analogue or AVO type meter.
Andrew
Happiness is a T70 at full chat!
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Thanks for your help. I'll see if I can work the above out.
Reggie
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When was the oil last changed, you can get strange CO readings from fed back fumes if the oil is old.
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It's just coming up to one year and six thousand miles. I've actually already bought the new oil and filter as I change it (on this car) at one year or six K, whichever comes first, but I shall definately do it now before the re-test just incase.
Thanks for that.
Reggie
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I put a car back on the road that had been standing for a while. This got some horrible readings which ended up being down to the fuel "going off" in the tank. Fresh fuel cured the problem....Not sure if the car you are talking about has been standing, but perhaps some fresh fuel or maybe a higher octane rating might help ?
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No, this car is in regular use. I've filled it with Shell optimax (and Wynns fuel cleaner). Andrew T suggested that I check the air filter (which I have yet to do) but a collegue at work has suggested removing the air filter. I assume that the lambda sensor would be able to compensate for this if it's working properly. Does anybody know if CO is produced from a rich mixture or a weak mixture? It looks as if it is now going to be next Monday or Tuesday before I can get it re-tested now.
Reggie
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There's some useful looking info on emissions problems at the link below:- www.bobmckay.co.uk/p_emissions.html#faultfind
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Thanks for that SpamCan 61. Fairly helpfull except that on my customer copy of the emissions test there is no reference to "lambda high", or "lamda low" to tie it in with the diagnosis.
Reggie
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The car has passed its emission test today. Oh happy day!
All I have done is:
1. Driven it for 250 miles with Wynns fuel cleaner.
2. Given it a good thrashing.
3. Sealed the miniscule leak on the back box.
4. Took the air cleaner off (which didn't look too bad).
5. Changed the engine oil and filter as it was due its service.
Although I will never know, I do just wonder which of the above "cured" it.
Thanks for all of your advice.
Reggie
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Reggie
Probably 1 & (particularly) 2; the often recommended 'Italian Tune-up'.
Good news!
Regards
John S
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