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Hey br/o/s, I come to you seeking help today. This could be a challenge for some of ythe more mechanically inclined on this board.
I have given my fair share of advice on this board, and now I could use some myself because i have encountered something I don't understand.
I drive a 2006 Cadillac CTS. It has a 3.6 liter v6 engine. When I got it, it idled rough and gave a OBD code p0420 and p0430 which meant that the catalytic converters were bad.
I also got about 15 mpg average even though it's supposed to get 18 city and 26 highway.
>After changing converters, mileage is still abysmal in the city.
It seems to eat gas insanely while idling, even though on the highway the screen (which can track MPG for all you who don't know caddy's out there) it gets well over 20.
The other known issues with the car are that its tires needed a LITTLE inflating (not that much) and it needs a new driveshaft coupler bushing.
But how the hell is my MPG this low? I asked the mechanics to check my O2 sensors for dirt and they said they were (probably) fine which probably just means they were too damn lazy to take a look. None of the known issues with the car can cause MPG to be this low.
>I hope it's the O2 sensors but the car isn't throwing any OBD codes for them
Anyone know what the hell can cause my MPG average to 15 with brand new converters?
Reply to this post and I will provide more details.
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>>17795510
are you driving strictly in the city?
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>>17795525
for the most part yes. I get on the highway sometimes, but rarely. It's mostly to go to work as of right now and that's in the city. Soon I will be driving it mostly highway to college.
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>>17795530
that sounds around right. try accelerating more gently from a stop.
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>>17795510
> Tires need inflaiting
There goes 15% of your mpgs, at least
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You could take it to a dyno guy and have him give you an economy tune or something. But that's $. Do you usually carry passengers and/or stuff in the vehicle?
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Have you checked your engine air filter? Spark plugs? Start with the basics before you start dumping tons of money into it
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>>17795555
No I do not.
>>17795554
Perhaps you're right.
>>17795548
I baby the thing, that's why I'm confused.
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>>17795616
Maybe I should. Can air filters and spark plugs do that without throwing a code though?
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>>17795510
O2 sensors don't always throw codes, a lot of the time they just assume your shitbox is dying and put it into open-loop trim tables as if it were forever cold.
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>>17795716
i'm sorry I don't understand could you please rephrase that? Also I'd prefer it not to be a shitbox as it is a cadillac.
You're saying the sensors could be bad but not throw a code and make it keep pumping fuel into the engine?
Would this be the upstream sensors or the downstream?
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Converters don't go bad by themselves until they're ancient. Usually means the engine mixture is off, in your case probably rich.
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>>17795731
So what can cause a car engine to run rich? Would mechanics be able to diagnose it for a reasonable price or am I stuck figuring this out by myself?
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