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Backfire or Pop When Starting Cold Engine

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Old 10-06-2011, 03:30 PM   #1
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Backfire or Pop When Starting Cold Engine

I searched and found old threads on the subject, but too old to bring back up. Seems to be common, but I only read where one person left their rig at the Dealer overnight so they could hear it for themselves. They said there was nothing wrong.

Mine is a 2011 model with only 2,500 miles on it. I never noticed the pop till my other half heard it the other day, and said something. Now, I hear it when I start the engine when it is cold. Itís a little bothersome, but it almost seems to be normal from what Iíve read so far. Sure doesnít seem like something like that should be normal. Should I just ignore it?
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Old 10-07-2011, 09:23 AM   #2
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Mine still does it at times...there is a theory that gases are trapped in the exhaust system on shutdown and this creates the "backfire" on start up the next day.
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Old 10-07-2011, 09:26 AM   #3
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I think we've read through the same threads.

Several people reported that their trucks don't do it any longer if they let it idle for 20 to 30 seconds before shutting it off.
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Old 10-07-2011, 11:30 AM   #4
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I think this is normal and is caused by the emissions blower motor. It forces fresh air into the exhaust manifold during cold startup in order to continue burning the unburned fuel in exhaust gases. All that extra oxygen is bound to cause flash burning and the resulting 'pop' that we hear
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Old 10-07-2011, 02:59 PM   #5
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mine makes a few little pops when it starts but u have to be outside of the truck near the exhaust to hear them
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Old 10-08-2011, 09:10 AM   #6
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Thanks for the feedback. Guess I'll ignore it, but it does make me imagine the truck runs rough while diving it. Wonder why it pertains to this engine? I think, tho I could be wrong, I have the same engine in my 2007 Camry, and it doesnít do it.
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Old 10-08-2011, 11:24 PM   #7
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Happens to mine only when it gets cold out
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Old 10-09-2011, 06:06 AM   #8
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Quote:
Originally Posted by wingspar View Post
Thanks for the feedback. Guess I'll ignore it, but it does make me imagine the truck runs rough while diving it. Wonder why it pertains to this engine? I think, tho I could be wrong, I have the same engine in my 2007 Camry, and it doesnít do it.
Next time you're ready to cold start, pop the hood first and locate the emission blower motor. It's mounted on the truck body infront of the engine on the passenger side. It's round and has a black plastic housing, plain as day.

Start the truck then go back to engine bay. You'll notice that the blower motor sounds like a like a shop-vac running. It will stay running for about 8-10 seconds. Once it shuts off, the ECU goes into closed loop mode and the idle will settle down.

During the time that the blower is running is when you'll notice the 'pops'. I believe this is the continued burning of fuel, which is the point of the blower in the first place. The V6 Tacoma engines do not have this. A co-worker has an '07 Camry, and I didn't see a blower on that engine either (2.4L engine).
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Old 10-09-2011, 11:02 AM   #9
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Quote:
Originally Posted by ecoterragaia View Post
Start the truck then go back to engine bay. You'll notice that the blower motor sounds like a like a shop-vac running. It will stay running for about 8-10 seconds.
I think I know what you're talking about. You basically just look down and to the left and there's this air pump.

Is this shutdown the disembodied VRRROOEEAAM sound I notice under the hood after cranking the truck? When I leave work tomorrow I'll pop the hood and get out to listen.
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Old 10-10-2011, 08:57 PM   #10
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Normal both of mine do it .
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Old 10-11-2011, 10:14 AM   #11
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Quote:
Originally Posted by ecoterragaia View Post
Next time you're ready to cold start, pop the hood first and locate the emission blower motor. It's mounted on the truck body infront of the engine on the passenger side. It's round and has a black plastic housing, plain as day.
I found the blower. Little almost flat round thing. I could not really hear much of a difference between startup and after the engine rpmís slowed down. Kind of gets lost in all the other engine noise. I even video taped the exhaust pipe. No pop or backfire. It was about 64 degrees with a light rain, so maybe it wasnít cold enough?
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Old 10-11-2011, 12:09 PM   #12
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My 2007 never did this, my 2011 does, it kinda starts rough. Like it hesitates prior to starting.
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Old 10-12-2011, 06:20 PM   #13
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It popped today, and it was about 54 degrees outside. Is there a certain outside temp that one always gets the pop/backfire? Iíd like to set the video cam up and actually capture one.
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Old 10-12-2011, 06:23 PM   #14
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We have two identical 2009 2.7 5speed trucks at work. I drive one of them. Mine has done it every morning since I have had it. It's got 54K on it now. The other truck probably has 30K on it and my co worker who drives it has commented on the same noise on cold starts. I don't know what it is, but it seems to be common and harmless.
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Old 10-18-2011, 08:53 AM   #16
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Glad it isn't just mine.
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Old 10-25-2011, 05:58 PM   #17
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Mine hasnít done it since I posted last. Iíve set the video cam up to tape it twice, and it didnít happen either time. Kind of like when you take a vehicle that is acting up to a mechanic, and it purrs like a kitten for him.
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Old 10-26-2011, 12:49 AM   #18
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Quote:
Originally Posted by wingspar View Post
I searched and found old threads on the subject, but too old to bring back up. Seems to be common, but I only read where one person left their rig at the Dealer overnight so they could hear it for themselves. They said there was nothing wrong.
Mine is a 2011 model with only 2,500 miles on it. I never noticed the pop till my other half heard it the other day, and said something. Now, I hear it when I start the engine when it is cold. Itís a little bothersome, but it almost seems to be normal from what Iíve read so far. Sure doesnít seem like something like that should be normal. Should I just ignore it?
I have same Taco as you and never had a problem.
And a thread is never "too old to bring back up" you post to it and presto it's alive again.
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Old 11-10-2011, 04:47 PM   #19
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Mine's done it once or twice, almost certainly a pop and not a backfire. I theorize it's the release of a little stored tension from the contraction of the cold
.
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Old 11-17-2011, 04:38 PM   #20
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noticed this multiple times once it started getting cold. doesnt seem like it should be normal but oh well! but why does the emission blower only do this when its cold out?
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