96 BMW 328is failed Smog Test! P0455 P0442 P0420

Hey this looks bad and I need your honest opinion before I head out to my mechanic who will rob me. No kidding!
My car initially failed the Fuel Cap Functional test and the System
Malfunction light. The check engine light was on! The error codes it produced were:
P0455 - Evaporate Emissions Control System Leak (gross leak) P0442 - Evaporate Emissions Control System Leak (small leak) P0420 - Catalyst System Efficiency Below Threshold (Bank 1) - I haven't serviced my O2 sensors my car had 118,000 on the odometer - I know i was technically supposed to do it at 100,000....
The other thing thats really strange is that my car fails the test at 15 MPH but passes at 25 MPH! At 15MPH my car is producing WAY too much Hydrocarbons (162, max allowed 54) and too much CO (88%, max allowed 50%).
Need your input. Really appreciate it! My mechanic is a dbag....
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On Mon, 18 Feb 2008 01:34:20 -0800 (PST), snipped-for-privacy@gmail.com wrote:

The two codes concerning leakage indicate your gas cap is in need of a new gasket (maybe a new cap if just the gasket can not be replaced). Its also possible you have a rubber line somewhere in the evaporative system that is shot and needs to be replaced.
The P0420 code woudl indicate you might need new O2 sensors since they regulate both hydrocarbon and CO levels. I believe your car has 4 of them, two on the exhaust manifold, one before the converter and one after. I'd start with the two on the exhaust manifold since those behnd the converter are the last to fail.
Find a new mechanic.
RJD
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A little less than two years ago I did a complete vacuum test during which my mechanic fixed/replaced fuel lines and hoses, fixed the gasket, and installed a new fuel cap. I don't know why the evaporate system is faulty again......Could this all be occurring simply due to a unsecured fuel cap---I don't think I tighten mine till it clicks.
I'll service the pre-cat O2 sensors soon.
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A little less than two years ago I did a complete vacuum test during which my mechanic fixed/replaced fuel lines and hoses, fixed the gasket, and installed a new fuel cap. I don't know why the evaporate system is faulty again......Could this all be occurring simply due to a unsecured fuel cap---I don't think I tighten mine till it clicks.
I'll service the pre-cat O2 sensors soon.
Yes, the codes could be the result of an unsecured gas cap. You can't blame this on the mechanic.
Jim
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Thanks for the tip. I'll tighten the gas cap and make it happy...
Now as for P0420 Catalytic Efficiency Below Threshold (Bank 1), do you think this is an issue of too much city driving in 1st and 2nd gear?! The cats may be collecting WAY too much rich fuel from the pre-cats O2 sensors which remains unburned in the cats. Could this be the reason that I'm failing the smog test? Maybe a hard drive on the freeway for 30 minutes would fix this---making the cats hot enough to make them efficient?
Or do you think I shouldn't second guess my failing pre-cat O2 sensors and simply replace them?
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Thanks for the tip. I'll tighten the gas cap and make it happy...
Now as for P0420 Catalytic Efficiency Below Threshold (Bank 1), do you think this is an issue of too much city driving in 1st and 2nd gear?! The cats may be collecting WAY too much rich fuel from the pre-cats O2 sensors which remains unburned in the cats. Could this be the reason that I'm failing the smog test? Maybe a hard drive on the freeway for 30 minutes would fix this---making the cats hot enough to make them efficient?
Or do you think I shouldn't second guess my failing pre-cat O2 sensors and simply replace them?
I think that you should replace the O2 sensors. Failed O2 sensors cause many problems, and one of them is a too rich mixture which contributes to cat failures. Not only that, but the rich mixture is not as efficient as the correct one. Hence, your mileage suffers from O2 failure as well.
O2 sensors are rather fragile and work in a very hostile environment. Thus they fail quite often with no apparent reason.
Jim
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