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Old 02-24-2011, 21:51   #1 (permalink)
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Car goes 'boom' after you start it

Here's a good one for you guys. When we took the car out on Sat., it seemed like every time I started it, you could hear, and feel a little 'boom', like 5 or 10 seconds after it starts. Don't know what that is? Kind of reminds me of a backfire. It only seemed to do it when the car was shut off for a short period of time (like when we were in a store). If the engine is cold, it's OK. My wife drives that car to work, and she hasn't complained about it, so I know it's not happening to her. My '87 Olds was doing that, too. But, that car has a carb on it, even though it's a computer controlled carb, it's still a carb. That being said, it's not coming out of the carb, but seems to be inside the engine somewhere. But, getting back to this car, do these fuel injected engines backfire? What could this be? Other than the 'boom', the engine runs perfect. Nice and smooth. It isn't a big 'boom', but something that you can definitely feel. It's not as noticeable on my Olds, you almost have to anticipate it, and wait for it, or else you'll miss it. But, on this GM, it was a more prominent 'boom', and was felt quite easily.

I just thought it rather odd that I have two completely different cars, with vastly different engines (and fuel delivery), that do the same thing!

Any ideas?

John
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Old 02-25-2011, 02:12   #2 (permalink)
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Re: Car goes 'boom' after you start it

You haven't upset any Italian looking men recently , have you ??????
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Old 02-25-2011, 05:11   #3 (permalink)
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Re: Car goes 'boom' after you start it

I think if I did, it would be a 'boom' that would be much more intense! Plus, I don't think I'd be alive to ask what it is!

John
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Old 02-25-2011, 08:59   #4 (permalink)
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Re: Car goes 'boom' after you start it

That may be the A/C compressor kicking in.If it's on defrost or mix, that might be it. Try starting it with it off.
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Old 02-26-2011, 22:40   #5 (permalink)
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Re: Car goes 'boom' after you start it

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That may be the A/C compressor kicking in.If it's on defrost or mix, that might be it. Try starting it with it off.
Bert,

No, I had it under 'auto', and I didn't have it on defrost. But, I did drive it tonight, and it was sleeting bad, and the windshield was icing up, so I had to put it on defrost. But, tonight, I heard no 'boom'.

John
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Old 02-27-2011, 06:51   #6 (permalink)
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Re: Car goes 'boom' after you start it

It is the heater blend door closes .Nothing to worry about.
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Old 02-27-2011, 08:29   #7 (permalink)
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Re: Car goes 'boom' after you start it

It also could be one of the doors opening when the vacuum builds up after a start. If I don't use the heater for quite awhile, when I turn it on I get a door suddenly opening and it sounds like a thump.
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Old 02-27-2011, 13:47   #8 (permalink)
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Re: Car goes 'boom' after you start it

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It also could be one of the doors opening when the vacuum builds up after a start. If I don't use the heater for quite awhile, when I turn it on I get a door suddenly opening and it sounds like a thump.
I figured it was something simple like that! But, I wanted to ask, could be the case for all cars? I ask because my '87 Olds Cutlass does the same thing. Could that be what that is, too?

John
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Old 02-27-2011, 14:56   #9 (permalink)
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Re: Car goes 'boom' after you start it

On the Olds, it would do it even idling. If it only does it accelerating, even slightly, it would more than likely be the choke.
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Old 02-27-2011, 20:11   #10 (permalink)
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Re: Car goes 'boom' after you start it

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On the Olds, it would do it even idling. If it only does it accelerating, even slightly, it would more than likely be the choke.
The olds never did it while accelerating. It always did it like 5-10 seconds after I started it.

Hey Bert, since you're on here all the time, do you have any extra throttle body's that will fit my car? If not, where's a cheap place to get one? A bone yard?

John
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