Popping/Backfire
Thread Starter
VETERAN
Joined: Oct 2015
Posts: 592
Likes: 57
From: Dayton OH
2025 C5 of the Year Finalist - Unmodified
Popping/Backfire
Just recently this car has been popping or backfiring a lot.....usually slowing down and sometimes taking off from a light or turn...
Ant ideas ?? Seeing a tuner on Thursday to see if the tune has changed...
Ant ideas ?? Seeing a tuner on Thursday to see if the tune has changed...
Tech Contributor
Joined: Jan 2007
Posts: 19,453
Likes: 1,158
From: Dyer, IN
Instructor
Joined: Nov 2019
Posts: 162
Likes: 80
From: Central NJ
Do you have an OBD scan tool? I would check your fuel trims at idle and and under acceleration. Lots of backfire is indicating excess unburnt fuel. If your fuel trims are positive 10 percent or more, something is happening to tell the car to add more fuel.
Safety Car
Joined: Mar 2017
Posts: 3,770
Likes: 940
From: Orlando Florida
My '99 did similar shortly after a clutch change -- found that they had let the engine sag during the change, and the air bridge unions had slipped at two locations, allowing some leakage. Reset my air bridge junctions and it cleared up idle and deceleration.
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Instructor
Joined: Nov 2019
Posts: 162
Likes: 80
From: Central NJ
Not sure why you went to a tuner instead of a mechanic. Do you get any engine codes? Does the exhaust smell like fuel? The fuel trims and 02 sensors would show signs of the misfire on that side of the engine. You need to determine what's causing the misfire. I would do an engine leak down test to ensure the cylinder is sealed tight if the misfire is isolated to a specific cylinder. An air leak at a coupler or vacuum line would random misfire at low rpms.
Instructor
Joined: Sep 2018
Posts: 125
Likes: 42
From: US
I had a similar problem after installing long tube headers. It didn't happen right away, but a few months after I had the car tuned it developed a backfire and sputtered at WOT. I was mad and initially thought the tuner may have made a mistake. Then I started with the basics. Put the scanner on and drove it. A MISFIRE code on cylinder 5 appeared. So I thought maybe coil pack. I switched the pack with another cylinder and drove with the scanner. It still had the same problem. So I checked the plug wire. And after I pulled off the insulated wire sleeve I noticed a melted area on the msd boot. Deep enough to lose energy at higher rpms... this was my problem. I threw some silicone in there temporarily and larer picked up some accel wires with ceramic boots that won't melt on the headers. That cured my issue. Good luck.
Instructor
Joined: Sep 2018
Posts: 125
Likes: 42
From: US
I had a similar problem after installing long tube headers. It didn't happen right away, but a few months after I had the car tuned it developed a backfire and sputtered at WOT. I was mad and initially thought the tuner may have made a mistake. Then I started with the basics. Put the scanner on and drove it. A MISFIRE code on cylinder 2 appeared. So I thought maybe coil pack. I switched the pack with another cylinder and drove with the scanner. It still had the same problem. So I checked the plug wire. And after I pulled off the insulated wire sleeve I noticed a melted area on the msd boot. Deep enough to lose energy at higher rpms... this was my problem. I threw some silicone in there temporarily and larer picked up some accel wires with ceramic boots that won't melt on the headers. That cured my issue. Good luck.