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Old 01-14-2006, 10:28 AM   #1
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Question Unburned Gasoline out the Tailpipe ?

Well, my new RX-8 should be just about broken in now, yesterday she turned 2,000.

No mechanical problems so far -- fuel consumption still ranges from 14 to 22 MPG depending entirely on how and where I drive. Car still seems to run extremely rich with soot accumulation on bottom of tailpipes. I warm up the engine for about five minutes before driving off in the morning. Car is parked in an underground garage overnight and this morning one of my neighbors commented that she smelled gasoline in the garage. I "sniffed around" and sure enough the fumes were quite strong and coming from my exhaust! Anyone else notice this? I don't notice it once the car is warmed up.
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Old 01-14-2006, 10:34 AM   #2
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Why are you warming up for 5 minutes? Way better for economy and the engine to start driving gently right away. The engine will warm up much quicker being driven gently and reduce the rich warm up cycle.
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Old 01-14-2006, 01:27 PM   #3
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The soot accumulation is "normal" as is the very rich fuel-air mixture at start-up. As beachdog says, you really shouldn't let the car sit and idle for 5 minutes to warm up. As long as you keep the revs below 3K or so until warm up, you can drive off after 30 secs to 1 minute. Not only does idling for that long burn fuel unneccesarily, it's not particularly good for the engine and other components.
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Old 01-14-2006, 01:27 PM   #4
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Sounds like our mystery might be solved.
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Old 01-14-2006, 01:54 PM   #5
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ok...but what if you start driving and stall it after 1 minute. Isn't that a recipe for flooding?
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Old 01-14-2006, 02:03 PM   #6
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Yea i talked to my mazda dealer, and the mechanic said that it's not good to leave it idle to warm up as you would a regular engine.... When i start my car up in the morning I smell a little mixture of gases which is normal, but if it's really bad maybe you have a problem, but i doubt it.. is your garage a confined area, and does it have enough air coming in and out? because maybe if theres no where for the gas fumes to go it's just lingering around in your garage...... Well if you stall out, yes it could potencially flood your car, but i doubt it, then again each 8 is different.... The first day i got my car i stalled due to the tricky clutch, but i didn't have any flood problems the next time i started it... don't worry your car is fine... have fun driving!

Last edited by Rotary78; 01-14-2006 at 02:05 PM.
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Old 01-14-2006, 02:05 PM   #7
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i think the chance of stalling within 5 min of startup is exceedingly low unless you just started learning how to drive stick then the odds would be exceedingly high hehe
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Old 01-14-2006, 02:35 PM   #8
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Thanks for the responses and for not flaming this newbie too badly.

Yeah, the dealer suggested 1 or 2 minutes minimum warm-up. I have driven clutch all my life, in fact have only 2 automatics out of 20 or so cars I've owned in my lifetime. My last car was a 5-speed Miata which I had for 4 years and sometimes miss (but other times don't). I have only stalled my RX-8 once, the second day I owned it.

My only concern is the very steep ramp leading up to the street from the parking garage under the building where I live. It does require a bit of throttle and I really can't bring myself to power up it with a stone-cold engine. Oh and yes BTW the garage does have very poor ventilation.
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Old 01-14-2006, 05:32 PM   #9
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Are you on the latest flash, that was supposed to lean out the car a bit. Worse comes to worse get a Canzoomer piggyback, and you can tune out the richness yourself, not too mention get some hp out of it.
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Old 01-14-2006, 05:59 PM   #10
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I've got some of the soot on the lower lip of my pipes too. I've had the 8 for 4 weeks and noticed it the first few days. I just attributed it to the fact that the engine burns <some> oil by design.
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Old 01-14-2006, 07:25 PM   #11
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Soot at the tailpipe is from the oil being burned by the engine - that's normal. There shouldn't be any "unburned gasoline" coming out of the tailpipe - that's what the CAT converter should be taking care of. If you had unburned gas coming out of your tailpipe you'd fail emissions inpsection (if it's required by your state). The RX8 does use a lot of gas when starting cold.
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Old 01-14-2006, 08:19 PM   #12
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No doubt it would fail emission test when stone cold. Here in CA our vehicles are supposed be thoroughly warmed up before the inspection. Wouldn't a steady diet of "unburned gasoline" destroy the CAT in short order? I have thought about taking the car in for a strictly "voluntary" smog check just for the heck of it. If it failed then for sure the dealership would have to work on it.
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Old 01-14-2006, 09:02 PM   #13
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From your description it doesn't really seem like you have a problem. Gas mileage doesn't indicate rich running. Yes, a lot of unburned gas going into the CAT would melt the inside and you'd have other symptoms (no power, can't rev, etc.). Most day-to-day CAT problems should trigger a check engine light. Getting an emissions test wouldn't hurt. If it failed. Mazda would have to fix it.
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Old 01-14-2006, 09:24 PM   #14
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Quote:
Originally Posted by Ericok
There shouldn't be any "unburned gasoline" coming out of the tailpipe - that's what the CAT converter should be taking care of.
The cats can't work miracles. If too much unburned fuel hits them at once, it will go right out the pipe. Proof = tailpipe flames
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Old 01-16-2006, 10:35 AM   #15
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Originally Posted by Torchmonkey
ok...but what if you start driving and stall it after 1 minute. Isn't that a recipe for flooding?
It increases your chances. To mitigate that I back in if I'll be parked all night or all day. I don't stall much, but by cutting out that whole backing-up to pulling-away transition I eliminate one scenario for a cold stall.

However, I'd agree with Freddie, the upramp would be the bigger concern.
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Old 01-16-2006, 11:53 AM   #16
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Quote:
Originally Posted by Torchmonkey
ok...but what if you start driving and stall it after 1 minute. Isn't that a recipe for flooding?
that's what I was very concerned about. And I HAVE stalled after 1 minute or so.

However, some members pointed out that restarting right after a stall is pretty unlikely to cause flooding. The issue is primarily with cars left overnight or for a while after being shut off cold.
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Old 01-16-2006, 11:53 AM
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