Backfires when slowing down
Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,464
Likes: 48
Backfires when slowing down
Hi Everybody,
My 1989 Corvette 6 spd with stock engine has been backfiring when I slow down. Usually after I have opened up a little. I was thinking this could be an exhaust valve. I am going to check the compression this weekend. Could it be an exhaust valve. Does anyone have other suggestions. This started from no where. The car was and still is running great. But, if I throttle it and then slow down it backfires. The catalytic converter is on the car but empty.. I tightened the exhaust manifold to the y pipe studs so much I'm afraid I'm going to shear them off.
Thank you
My 1989 Corvette 6 spd with stock engine has been backfiring when I slow down. Usually after I have opened up a little. I was thinking this could be an exhaust valve. I am going to check the compression this weekend. Could it be an exhaust valve. Does anyone have other suggestions. This started from no where. The car was and still is running great. But, if I throttle it and then slow down it backfires. The catalytic converter is on the car but empty.. I tightened the exhaust manifold to the y pipe studs so much I'm afraid I'm going to shear them off.
Thank you
Race Director
Joined: Jun 2020
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From: north of Chicago
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Hi Everybody,
My 1989 Corvette 6 spd with stock engine has been backfiring when I slow down. Usually after I have opened up a little. I was thinking this could be an exhaust valve. I am going to check the compression this weekend. Could it be an exhaust valve. Does anyone have other suggestions. This started from no where. The car was and still is running great. But, if I throttle it and then slow down it backfires. The catalytic converter is on the car but empty.. I tightened the exhaust manifold to the y pipe studs so much I'm afraid I'm going to shear them off.
Thank you
My 1989 Corvette 6 spd with stock engine has been backfiring when I slow down. Usually after I have opened up a little. I was thinking this could be an exhaust valve. I am going to check the compression this weekend. Could it be an exhaust valve. Does anyone have other suggestions. This started from no where. The car was and still is running great. But, if I throttle it and then slow down it backfires. The catalytic converter is on the car but empty.. I tightened the exhaust manifold to the y pipe studs so much I'm afraid I'm going to shear them off.
Thank you
Race Director
Joined: Jun 2020
Posts: 10,685
Likes: 2,249
From: north of Chicago
2025 C2 of the Year ('64-'66) Finalist - Unmodified
2025 C3 of the Year Finalist - Modified
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2024 C4 of the Year Finalist - Modified
2023 C2 of the Year Finalist - Unmodified
2023 C4 of the Year Finalist- Modified
2022 C4 of the Year Finalist - Modified
2022 C3 of the Year Finalist - Modified
2021 C7 of the Year Winner -- Modified
2020 C4 of the Year Finalist - Modified
My other thought is O2 sensor failure causing a rich exhaust on on hot pipes causes back fire.
Safety Car
Joined: May 2001
Posts: 4,757
Likes: 1,647
From: Fairfax Virginia
On Tuner pro you should be able to identify which side is getting air when decelerating.
I am a bit doubtful of the scenario of a bad Oxygen sensor causing this. O2's can do a lot of weird things to your Corvette and they do like to fail in the rich mode but that would not cause popping I don't think. I would check all your vacuum lines and be sure they are all holding tight. Be sure to check the EGR Vacuum Solenoid mounted on one of the thermostat housing bolts. It is supposed to have vacuum going to it to control it. Do you still have the EGR valve in your Corvette? Does it function properly? Test it by applying a vacuum to the vacuum line that operates the EGR valve. When you apply vacuum the EGR diaphragm will move and the idle will change a bit. A faulty EGR can be a PIA to fix but makes the engine run so much better afterwards.
The air entering might be from around your exhaust manifolds bolted to the heads. Check the bolts holding the headers or exhaust manifold depending on what your Corvette has. Decelerating with a tiny air leak will cause that lean popping.
I am a bit doubtful of the scenario of a bad Oxygen sensor causing this. O2's can do a lot of weird things to your Corvette and they do like to fail in the rich mode but that would not cause popping I don't think. I would check all your vacuum lines and be sure they are all holding tight. Be sure to check the EGR Vacuum Solenoid mounted on one of the thermostat housing bolts. It is supposed to have vacuum going to it to control it. Do you still have the EGR valve in your Corvette? Does it function properly? Test it by applying a vacuum to the vacuum line that operates the EGR valve. When you apply vacuum the EGR diaphragm will move and the idle will change a bit. A faulty EGR can be a PIA to fix but makes the engine run so much better afterwards.
The air entering might be from around your exhaust manifolds bolted to the heads. Check the bolts holding the headers or exhaust manifold depending on what your Corvette has. Decelerating with a tiny air leak will cause that lean popping.
Le Mans Master
Joined: May 2004
Posts: 5,866
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From: Hellinois
Finalist 2020 C4 of the Year - Modified
I just replaced my transmission so I had th exhaust off the car too. I took every joint apart, (slip together w/ band style clamp.) and I was amazed at how many small leaks I had. I used the high temp RTV on each joint and replaced a couple clamps. The first thing I noticed when I got the car back on the road was that it did not backfire any more.
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Team Owner
Joined: Oct 2004
Posts: 81,241
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From: altered state
St. Jude Donor '05
5,0s used to have a problem like that it was the diverter ?? valve in the smog system. Is it a loud pop or a real backfire
The LT5, same thing -solution was to take fuel out on decel
The LT5, same thing -solution was to take fuel out on decel
Last edited by cv67; Sep 19, 2020 at 03:47 PM.
Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,464
Likes: 48
So I get under the car. High temperature gasket sealer in hand. Ready to seal all the leaks. And rid myself of the dreaded backfire. The exhaust looks Fn beautiful and original. The resonators are in place and it looks like the system is welded like from the factory. So I just did not have the heart to start taking it apart. So it is going to backfire for a while longer, Thank you all
Pro
Joined: Aug 2020
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From: Liliha Bakery stuffing my face with coco puffs!
Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,464
Likes: 48
I did not get the chance to run TunerPro. I changed the multifunction switch in my Impala. Tried to figure out how to remove the rear hatch latch. And just got tired of working on cars today. But, the exhaust looks so tight. If I take it down I'm going to need to replace it. So next weekend. Look at plugs. Run TunerPro and hope for the best.
Thank you
Thank you