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  #1 (permalink)  
Old 06 Oct 2018, 09:31 am
loomex's Avatar
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Default Back firing

My poor little Christine is backfiring when I downshift. There no issues with acceleration. I can mash the pedal and it goes. The backfiring seems to happen when I downshift or use the engine for braking as in going down hills. The plugs (gapped at .04) and wires were replaced last summer, the cam sensor was replaced last summer and the timing belt was replaced in February. I have no codes and the car runs fine. It's an 02 NA 5sp.
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Old 06 Oct 2018, 10:33 am
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Default Re: Back firing

How are you checking for codes?

Do you have an exhaust leak?

Does it backfire if you don't use the brake when going downhill? I would check the vacuum line going to the brake booster.
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Old 06 Oct 2018, 12:09 pm
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Default Re: Back firing

Quote:
Originally Posted by ptcruisersteve View Post
How are you checking for codes?

Do you have an exhaust leak?

Does it backfire if you don't use the brake when going downhill? I would check the vacuum line going to the brake booster.
No codes are showing up

I will have to crawl under and check for leaks, but I don't believe I have any

The next time I drive it, I will listen for any change while braking
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USAF 83-92, IRR 92-94, NV ANG 94-98, IRR 98-00
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Old 06 Oct 2018, 01:04 pm
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Default Re: Back firing

I would suggest hooking up a vacuum gauge to see what the needle does if you have one.

A vacuum gauge is not the proper direction for troubleshooting a backfire it might tell us if the timing is okay. Checking the fuel pressure, and exhaust restrictions might help us but we can do any diagnostics that we can without gauges first.

How is the acceleration?

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Last edited by ptcruisersteve; 06 Oct 2018 at 01:28 pm.
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Old 06 Oct 2018, 04:01 pm
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Default Re: Back firing

you must be having a hole in your catalytic converter. once the cat is removed or has a hole you can hear pops when you decelerate. the cat helps to muffle a lot of the sound. that's my theory anyway. i run a straight Y-pipe with syked tune engine management software, it's designed to pop very loudly when decelerating. i like the noise although.,
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Old 06 Oct 2018, 06:39 pm
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Default Re: Back firing

ptcruisersteve,
My acceleration is great with no issues. I have a vacuum gage, but would not know where to hook it up for testing

_PTGT03,
Removing the catalytic converter is a big no-no in NYS
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Old 06 Oct 2018, 07:12 pm
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Default Re: Back firing

I've connected a gauge to a vacuum port at the throttle body area. My 2.4 NA PT typically does around 17.5 InHg at idle.
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Old 06 Oct 2018, 07:46 pm
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Default Re: Back firing

Quote:
Originally Posted by loomex View Post
ptcruisersteve,
My acceleration is great with no issues. I have a vacuum gage, but would not know where to hook it up for testing

_PTGT03,
Removing the catalytic converter is a big no-no in NYS
When you do get the vacuum gauge hooked up see what happens when you decelerate quickly. See if it matches post #4 on quick deceleration.
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Last edited by ptcruisersteve; 06 Oct 2018 at 07:58 pm.
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  #9 (permalink)  
Old 07 Oct 2018, 02:41 pm
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Default Re: Back firing

Quote:
Originally Posted by ptcruisersteve View Post
When you do get the vacuum gauge hooked up see what happens when you decelerate quickly. See if it matches post #4 on quick deceleration.
Where, exactly do I hook up the gage?
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USAF 83-92, IRR 92-94, NV ANG 94-98, IRR 98-00
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Old 07 Oct 2018, 05:02 pm
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Default Re: Back firing

Quote:
Originally Posted by loomex View Post
Where, exactly do I hook up the gage?
You can connect a hand vacuum gauge to the intake manifold either tee into the PCV or the brake hose. Than start your engine and report what the gauge is doing.
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