Quote:
Originally Posted by dcb
Elephant! from typical diagnosis procedures:
AUTO REPAIR HELP - DIAGNOSE - EMISSIONS TEST FAILURE
If you have high HC AND CO, then the cat is suspect, but it is pretty low on the list of suspects. Your CO is nowhere near high in any of the tests.
High HC by itself looks like ignition mostly suspect, and then vacuum leaks.
Note, you had a HUGE spike in NOX in the third test also, like EGR went wonky or something.
You could have several things going on, emissions are not simple to diagnose, don't pretend that they are.
I'm reminded of how many folks would replace the carb when the carb isn't even the problem. |
I just want to say, dcb, that I agree with you that the diagnosis is not complete and that this is still just a logical, educated guess. I just think it is a good guess. But separately from that emissions-failure diagnosis-debate, there is a good eco-driving principle in heating the cat up to operating temps through light-load idling at or near the start of a drive and then begin hypermiling. If I do that, I can be much more confident that 80% load acceleration in a P&G cycle will not mean unnecessary pollution. I also appreciate better now that DFCO, especially with the engine off, will send a lot of relatively cool air through the cat, possibly interrupting its operation if the DFCO jag is long enough. So, I agree that the diagnosis has not conclusively pointed-out the cat, and I agree there could be more than one problem. However, I also have to recognize the cat is likely at least ONE of the culprits for the emissions failure. As an aside, another reason I have decided to go back to engine on coasting on the freeway is that it feels like I'm abusing my transmission by bumping it at those speeds, and I really love my car. Even engine-on, I should be able to reach this year's goal of keeping the car over 60 mpg without super radical hypermiling and stress on parts.
Sentra: when you test to see about lighting the CAT today or whenever, to see how long it takes, could you record how far you drove in miles or tenths of a mile as well as coolant temps when the cat reaches temp? My car does not have a CAT temp sensor and knowing distance and coolant would give me rough indexes of how long/far to idle to be in the right ballpark. Otherwise I'll just guess a mile or two minutes idling.
Many thanks.