A year ago I had a complete new exhaust made for my 2002 C4S. Lovely gas flowed, equal length headers, 200 cell Cats, fabricated silencers and new Bosch Lambda sensors fitted, all very nice. However every now and then the Check Engine Light pops on , usually when there is a very light throttle/load at about 2800 RPM. The car is also using more fuel than it did before the new exhaust was fitted. Something is amiss ! Any ideas out there please ?
check engine light problem
- Thread starter rapid1
- Start date
Do you have the fault code(s)?
Very wise to get the fault codes read before doing anything. Some diag tools will look at live traces from the lambda sensors which can provide extra cluess as to what is going on.
I suspect that the ECU assumes the cats aren't working and you'll get an ageing fault (Common on sports CATs). A fix for this is to put in lambda spacers on the rear sensors - this has worked well for my customers.
Start with code reader though!
Kind Regards Lee
I suspect that the ECU assumes the cats aren't working and you'll get an ageing fault (Common on sports CATs). A fix for this is to put in lambda spacers on the rear sensors - this has worked well for my customers.
Start with code reader though!
Kind Regards Lee
JuliusF
New member
All good advice above, but I understand the position of the Lambda sensor in the gas flow can cause intermittent problems of the type you describe, and throw lambda errors - sometimes you need it further out/in and most commercially available kits come with sensor spacers to adjust the depth into the flow.
Mine actually caused intermittent problems with one sensor(?) with the spacers fitted, and corrected itself once the spacers were taken away.
Might be worth experimenting.
J
Mine actually caused intermittent problems with one sensor(?) with the spacers fitted, and corrected itself once the spacers were taken away.
Might be worth experimenting.
J
Thank you all for your very helpful comments. I think we may have cured it by fitting a new MAF sensor . The tests showed that it was indeed the after-cat Lambda sensors (new and correct) that were giving the codes but it was suggested to me that we try a new MAF because although they don't put up codes they do get old/tired. The engine is now slightly sharper and the mpg has improved by 10%, so happy days ! A re-map may get even better results but for now I think I should leave things alone............but who would you recommend ?!
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