3.6 smells rich, but no codes. (Also seems to have vanishing gas)
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Cadillac STS Forum - 2005 through 2012 Discussion, 3.6 smells rich, but no codes. (Also seems to have vanishing gas) in Past Cadillac Vehicle Discussion; Hi guys! Finally got my car back from the dealer. Needed a new computer, and everything is happy now. The ...
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    CadiTamer is offline Cadillac Owners Fanatic
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    3.6 smells rich, but no codes. (Also seems to have vanishing gas)

    Hi guys!
    Finally got my car back from the dealer. Needed a new computer, and everything is happy now.
    The car still smells rich, though... There's not any codes SAYING its rich, but it smells rich. Gas mileage is also poor. (Getting about 14 city... Figured i'd at least get 16 or 17) Are there any common issues with the 3.6 that could cause this? I read that intake manifold bolts like to work themselves lose on the N* (as well as head bolts), but does this apply to the 3.6 as well?

    The car has power, and it drives pretty well. It just smells rich at idle, and seems to drink gas while idling... That, or i have a fuel leak, and gas wasn't siphoned out of the tank by the sketchy dealer it was at for a week before it got moved to the Cadillac dealer. (I gave it to them on half a tank... got it back with .5 gallons left)

    I read that the gas tank on these cars is a horse shoe shape over the drive shaft. Would this cause what i'm seeing? If i park on hills, i've seen the gauge go from saying 7/8th of a tank to under half in less than an hour. I can't really find any rhyme or reason, though.

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    MoistCabbage's Avatar
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    I would check for a faulty FPR first.

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    ewill3rd is offline Cadillac Technician
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    Re: 3.6 smells rich, but no codes. (Also seems to have vanishing gas)

    If the engine was running rich, codes would set and the SES would come on. There are instances, particularly in cold weather, where the computer will force a rich mixture. If you have a raw gas smell coming from somewhere check for leaks. Another complaint I see a lot in the winter is people complain about their fuel mileage but fail to consider how much time their car is spending idling and warming up or driving at reduced speeds in the snow. When it idles you are burning gas and getting 0 mpg. It doesn't take many zeros for the computer to calculate a much lower average mpg.
    The STS tank does have a "saddle" shaped hump in the middle with 2 senders and one pump. The gage is buffered for several reasons but parking on hills, particularly at a side angle can cause fluctuations in readings.
    The gage isn't meant to be a 100% accurate measure of the fuel in the tank but a representation of approximately how much you have left.

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    CadiTamer is offline Cadillac Owners Fanatic
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    Re: 3.6 smells rich, but no codes. (Also seems to have vanishing gas)

    No raw gas smell, but there is what appears to be a little bit of moisture around the shield above the driveshaft. I'm not 100% sure if it's fuel or not, as i haven't had a chance to crawl under the car and smell around... There's just some dirt on the bottom of the fuel tank near that shield, and it looks like it's a little wet.
    I haven't seen any puddles on the ground, but the gauge is definitely showing less fuel after the car sat overnight. I know gas evaporates very quickly, and if there's a leak, i probably won't see it on the ground. I just feel like for there to be that much fuel going missing would make a fairly large stream somewhere.

    I only notice gas level changes while the car is off for a bit. If i'm driving around, it doesn't seem to do anything unusual.

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    Re: 3.6 smells rich, but no codes. (Also seems to have vanishing gas)

    If you want to see a car consume prodigious amounts of gasoline try operating it in extreme sub-zero temperatures. At -40F and colder 10MPG looks pretty good in my '06 North* AWD STS. During warmup the fuel mixture is determined by lookup tables rather than o2 sensors and the engine runs very rich until it gets to operating temp and switches to closed loop mixture control. You can almost see the gas gauge going down.
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    Re: 3.6 smells rich, but no codes. (Also seems to have vanishing gas)

    Yes! As an exercise to appreciate the difference in mpg in cold weather and before the car warms up, become familiar with your instant MPG read-out during mild weather on roads you drive often and know well. In my case it's out of my driveway and through the development. When you compare the mpg when just starting out in very cold weather, you'll see a huge difference in instant mpg than what you're used to when you begin to drive the car when it's very cold! For me very cold is teens or below.

    I'd venture to say the MPG is almost half of what it would be when the car is driven in warm weather and is "warmed up".

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    CadiTamer is offline Cadillac Owners Fanatic
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    Re: 3.6 smells rich, but no codes. (Also seems to have vanishing gas)

    Well, down here in Mississippi, "very cold" is anything below 30

    I have noticed the car sucks gas when cold, but that's nothing new to me. It's just strange for me for a car to smell rich, and use as much gas just idling as this one does.

    In other news, i've been sitting at half a tank of gas for about 50 miles now... Saw it bump up to 3/4 of a tank when i left church, and now it's about halfway between half and 3/4. This gas gauge and me wont' be getting along well...

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    Re: 3.6 smells rich, but no codes. (Also seems to have vanishing gas)

    thats almost shorts and tshirt weather here in MN. ... earlier this week it was -23°F air temp with about -43°F windchill, rumor has it that it was warmer on Mars than it was here.

    Maybe there is something going on with the fuel level sender?

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    Re: 3.6 smells rich, but no codes. (Also seems to have vanishing gas)

    If the gas tank appears "wet" in places, I would have someone check for a fuel leak.
    It is uncommon but certainly possible.
    Be sure it isn't from a leaking differential seal that is throwing grease onto the tank.

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    CadiTamer is offline Cadillac Owners Fanatic
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    Re: 3.6 smells rich, but no codes. (Also seems to have vanishing gas)

    I'll crawl under it after class today and see what the wetness smells like. Thankfully gas has a pretty clear smell.

    Still around half a tank... I'm beginning to think it's just a funny gas gauge, and someone siphoned gas out of my car while it was at the dealer... I wouldn't put it past them to steal my gas to put into one of their cars that's basically completely empty when people want to test drive them.

    Is the rich smell at idle, even after warmup (even a heat soaked engine) normal? Does the timing chain stretch issue cause reduced gas mileage? I haven't heard any noise from the front of the engine, but there is what sounds like a bit of a rattle when it first starts up. It sounds like something in the exhaust maybe rattling, but could it be the timing chain? The car has 127K on it, so i feel like if the chain was going to fail or stretch, it already would have...

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    Re: 3.6 smells rich, but no codes. (Also seems to have vanishing gas)

    When timing chains stretch it will set codes, it is fairly common on a 3.6 depending on the year.
    The gas gage on this car uses two senders and it is pretty strange sometimes.
    I'm still not sure where you say "smells rich". Truly the only way to tell would be to put it on an emissions analyzer to see if it is rich or not. Otherwise it is pretty subjective, and it is pretty unusual for an engine to run rich or lean to a noticable degree without a code setting of some sort.

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    Re: 3.6 smells rich, but no codes. (Also seems to have vanishing gas)

    So just wait till the cam codes pop up to replace the chains?

    Think of how the older (but still well running) Chevy trucks smell. Not a burning nose and eye kind of rich, but just basically the same smell.

    Noticed a quiet sound like maybe a bad bearing or something today while I was poking around under the hood. There does seem to be some noise for three or four seconds after it's been off for more than five hours. I feel like I'll probably be throwing a timing kit at the engine within the next year or so. Gonna change the oil tomorrow, as it's looking old, and the OLM wasn't reset when the PCM was replaced.

    The wet looking spot isn't fuel. Looks like it's just grime that's collected in that area.

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    Re: 3.6 smells rich, but no codes. (Also seems to have vanishing gas)

    Timing chains are a huge task on that engine, I wouldn't do them unless I had to. I have seen some with slack make noise before codes set. I have only seen 2 mechanically fail. Some years GM offered a special coverage on timing chain wear but I can't say if yours is involved or not.

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    CadiTamer is offline Cadillac Owners Fanatic
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    Re: 3.6 smells rich, but no codes. (Also seems to have vanishing gas)

    Quote Originally Posted by ewill3rd View Post
    Timing chains are a huge task on that engine, I wouldn't do them unless I had to. I have seen some with slack make noise before codes set. I have only seen 2 mechanically fail. Some years GM offered a special coverage on timing chain wear but I can't say if yours is involved or not.
    After doing the timing belt on my Plymouth Breeze (nearly involves taking the engine out of the freaking car), the timing chains on this car look pretty easy. Still, i don't want to do it before i have to. I'll give it a bit and see how fast it gets worse, and then go from there.

    What's the normal heavy-footed city driving MPG for these cars? I'm averaging about 15.6MPG with nearly 100% city driving. They updated the TCM when they replaced the PCM, so i'm sure that's why my gas mileage is up from 13MPG.

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    Quote Originally Posted by ewill3rd View Post
    Timing chains are a huge task on that engine, I wouldn't do them unless I had to. I have seen some with slack make noise before codes set. I have only seen 2 mechanically fail. Some years GM offered a special coverage on timing chain wear but I can't say if yours is involved or not.
    2007 STS/CTS/SRX LY7's are covered for timing chain failure for 10 years/120k. Looks like the OP is just over the 120k mark, it'd be worth looking into as a good dealer may help since the mileage is so close.
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