Cold backfire - Ford Mustang Forum
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Old 10-10-2016 Thread Starter
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Cold backfire

Any tips on this, only for maybe the first minute of driving, when I press the clutch to shift and the RPM's drop, I get a Kerpop backfire. It'll do this just once or twice, then fine. I also notice as the RPM's are going up before that, it's a little 'surge-ey' feeling. Ok, this is a dorky way to describe but like this...
(06, 5 speed, V6)

RRRRRRRRRRRRRRRRRRRRRRRRRR clutch RRRRRRRRRRRRR Kerpop

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Old 10-10-2016
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My gut tells me you're running rich, because your running a cold engine. As the engine and exhaust warms up burns all the fuel charge in the cylinder instead of the exhaust.

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2005 V6 Convertible
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Quote:
Originally Posted by MirageII View Post
My gut tells me you're running rich, because your running a cold engine. As the engine and exhaust warms up burns all the fuel charge in the cylinder instead of the exhaust.
so your thinking just plain running rich but the extra fuel only causes this when cold? What's weird, is in the first 30 seconds of starting, the whole exhaust must be ice cold still, so 'where' is the spark/heat coming from that ignites it? It is backing firing like right in the exhaust manifold? It's not a bang like you think of with a backfire, it's a more muffled 'ker pop' sound if that makes sense. So a tune might help rather than a funky O2 sensor or something?
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Old 10-10-2016
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It's not the running rich, it's the running cold. It's normal. Engines normally run very rich when cold started, or it would just die out. You probably also noticed that cold starting is louder than a warm start. The more free your exhaust is, the more you hear it. My neighbors have mentioned my cold starts, so far not in a bad way. Mine is running a Flowmaster American Thunder series cat back set up which is aggressive sounding but not obnoxiously loud.

Car makers have gone out of their way to make them more idiot proof for us. One way they did it, once the computer took over, was to make it possible to drive away while the engine was still cold, without having to operate a manual choke, or wait for the Automatic choke to stabilize the idle speed. There was a time when one had to wait 30 or more seconds for the engine to warm up enough before driving, or it would choke out. We don't have to wait now, even though we should. The ECM dumps enough fuel down the intake at cold start-up to light the coldest engine off. That's why the throttle plates open up a tiny bit at cold start too, to make sure there is enough air added to the mixture to keep from flooding the plugs out, then close off a bit as the engine starts to warm a bit. The fuel mixture leans out slowly back to optimum level as the head temperature comes up.

It is still, even with the most computer controlled engines, highly recommended to wait at least 30 seconds, on a warm day, before driving a cold started car, the colder the day, the longer one waits. Your valve train especially will thank you because it was just prodded into action with only 5/30 to protect it.

Sometimes, when it's quite hot out (Florida) I open both doors, start the car, get out and go listen to the exhaust crackle while the super heated interior cools off, and/or until the pop and crackle is gone, maybe a minute or more at times. It's a beautiful noise with a nice sounding cat back on. (Not a recommendation - these puppies drone heavily but I avoid loading the engine up at low revs if I can, to eliminate the drone. Drone, that's a whole different topic for discussion.)


130 total pounds of Pitbull ruled by 8 pounds of cat.
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Old 10-11-2016
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Dana W is correct, all engines are designed to run rich when cold, he explained it all better than I did. Thanks Dana W! The only thing I would add is that the catalytic converters heat up pretty fast and operate upwards of 900 degrees F. Those little backfires are more likely happening inside the cat, and that can shorten their lives. And if you live in California, the cats alone (2 on my 05 V6) will cost you about $800 ! So you may want to head Dana's advice, and let it idle a good couple of minutes and avoid the backfires if you can.

Have fun!


2005 V6 Convertible
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