Hello all, the car is a Daewoo Nexia, 1.5 16V, 1996. It failed its MOT last week. The results on the print out were.
fast idle
C0 0.762 fail
HC 95 pass
Lambda 1.017 pass
The natural idle test also failed on CO at 0.574 %
I thought it wasn't far off passing so I gave it a service, new oil, filter, plugs, air filter and a good Italian tune up and 25 miles drive, took it back for free retest. It failed again
CO 0.715 % fail
HC 98 pass
Lambda 1.022 pass
The natural idle also failed again on CO at 0.593 %
Last year it had a new cat and lambda sensor, any ideas please on what to look for?
Edited by Pugugly {P} on 15/10/2007 at 22:23
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Dogtooth
Common scenario; this is how it's worked through.
First; plug in and read any codes. Then check the live data for an obvious anomaly that can affect mixture - coolant temp etc. and correct it.
Check that the system has entered closed-loop - the oxygen sensor is being used by the ECU. Read the hot oxy sensor's output voltage to see if it's sweeping up and down; if it is, then check the cat's in and out temperature with a laser. Should be 50C hotter coming out.
If it's stuck rich; force it lean to check it and then find the source of the mixture fault - misfire; air leak; fuel pressure; incorrect parameter; MAF; MAP; TPS - whatever....
Easy, eh?
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was it a cheap copy type cat you had fitted last year?
i wont fit these anymore due to the hassles 12 months later,i would rather fit good s/h low mileage
i wonder if this has to do with cats fitted for aftermarket 2001 onwards having to be eu approved
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bb
You and me both wondered that; it's almost within the cat "window" of 0.4 percent CO.
As you say; cheap cats just aren't worth buying.
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Thanks for the replies.
Screwloose, yep its easy when you have a scanner, unfortunately I don't.
Bellboy, I have asked this question on another forum too and the feeling is with those test results that the cat is faulty. I'm not sure what sort of cat was fitted last year but it's looking like it could be that.
What do you think I should do now, will a scan show the cat is faulty or should I take a risk and buy another?
Thanks
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Dogtooth
I was being [trying to be] ironic.
It isn't easy at all - even with a scanner. Without one it's impossible to say what it is with any degree of certainty. Worth risking the £600-odd for a quality cat?
Scanning it won't prove conclusively that the cat is faulty - it only provides the necessary information to make a decision based on years of experience.
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i wouldnt put my hand up and say deffo buy a new cat either,its just what i have found with these cheap cats a year down the line,fine if you know the car is going to be far far away,not fine if customer lives 1 mile away
i seem to remember the ecu on these daywoos on this vintage used to lose their data as well and only a battery off and reconnected made them work again for a while,im sure i read that somewhere? backed up with a mint example in my local breaker a few years ago and me asking the reason why it was scrapped (as you do? well i do coz im nosy)
sorry cant really offer any more help
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Ok fellas, thanks for your help, I'll let you know the outcome.
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