Misfire after header install
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Misfire after header install
Hey all, I threw some headers and high flow cats on my c7 lt1 and now I'm have big time misfire issues. I am going to get the car tuned but it is really haven a hard time. The only code showing is the o2 sensor not liking the high flow cats but I've taken cats off of other cars for racing without this sort of issue. I put in some colder heat range plugs in at the same time but I'm almost thinking maybe one of the plug wires went south when removed. Any thoughts?
I'm going to be putting a lt4 blower on with fuel pump and injectors with all the trimmings, but if I start with a misfire that is unsolved I feel I might be asking for trouble.
I'm going to be putting a lt4 blower on with fuel pump and injectors with all the trimmings, but if I start with a misfire that is unsolved I feel I might be asking for trouble.
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Joined: Dec 2020
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From: Katy, Texas
Hey all, I threw some headers and high flow cats on my c7 lt1 and now I'm have big time misfire issues. I am going to get the car tuned but it is really haven a hard time. The only code showing is the o2 sensor not liking the high flow cats but I've taken cats off of other cars for racing without this sort of issue. I put in some colder heat range plugs in at the same time but I'm almost thinking maybe one of the plug wires went south when removed. Any thoughts?
I'm going to be putting a lt4 blower on with fuel pump and injectors with all the trimmings, but if I start with a misfire that is unsolved I feel I might be asking for trouble.
I'm going to be putting a lt4 blower on with fuel pump and injectors with all the trimmings, but if I start with a misfire that is unsolved I feel I might be asking for trouble.
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Joined: Dec 2020
Posts: 89
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From: Katy, Texas
The stock plugs are on there pretty good. When you instal new aftermarket plugs they do not stay on too well and don’t have that coil spring rebound aluminum thing...use electrical connection grease at the tip of plug. Did you instal new plugs? If so, did you drop one during instal? Where they Gapped?
also check your battery connection and make sure your battery holds charge and is connected properly. Maybe it was disconnected during the instal and improperly connected it back causing a surge. It can cause a misfire if your battery is faulty. Remember to think outside the box with these cars, it’s usually something that too obvious to consider with the C7.
misfire is from either electrical system, fuel and air flow. Sudden change usually leads to the electrical system. Start at battery and work your way to fuel system. Doesn’t hurt to clean MAF sensor either
Last edited by murrayphoto819; Mar 30, 2021 at 11:09 PM.
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That is exactly the problem I'm having. I figured that was the issue but wasn't sure.
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From: Katy, Texas
Aftermarket wires are hard and they will soften and get used to their spot after some driving with heat in the engine compartment....
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Joined: Dec 2020
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From: Katy, Texas
been there. Checked ignition wires? Tight? Get some electrical grease and dab a bit on plug before you plug them back in. Disconnect ground and check fuses in the rear.
Aftermarket wires are hard and they will soften and get used to their spot after some driving with heat in the engine compartment....
Aftermarket wires are hard and they will soften and get used to their spot after some driving with heat in the engine compartment....
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Don’t know if you removed the plugs prior to the header install but I’d check your plugs...it may be cracked and I’d also make sure your plug wires are firmly seated at both ends !!
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PRobably plugs and wires. One thing I've learned is to use the proper socket with rubber insert to remove the plugs and to not re-use the stock plug wires. They are prone to damage when removing. I've done half a dozen header installs on the C7, use the stock plugs or another heat range if needed, and use MSD plug wires that let you know they are plugged in. They click once on the plug and twice on the coil. NEVER had a misfire issue after header install.
Anyhow, point is, you likely have a loose or damaged plug wire or possibly a damaged plug.
Anyhow, point is, you likely have a loose or damaged plug wire or possibly a damaged plug.
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Update for anyone interested, I changed back to the ac Delco plugs from the ngk and problem solved. Guess my car didn't like those plugs for whatever reason.
Last edited by Scott Haymond; Apr 10, 2021 at 08:37 PM.
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So, I'm still having this issue. After a trip to the dealer, they couldn't figure it out. New ac Delco oem plugs installed, oem wires, stock tune in car. Still can't get the random misfire to go away. Does anyone think it's possible the o2 sensors are malfunctioning? The dealer didn't see anything that would be causing it. I'm so frustrated that a simple header install ruined my vette (driving wise) I'm about ready to pull the headers and just go back to the oem exhaust. Any ideas from anyone?
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A dealership couldn’t diagnose a misfire ??…that’s pitiful !!….are these long tube headers ??…sometimes these can cause O2 issues being that they are placed further back in the exhaust stream…are these misfires you can actually feel ??…you are better off taking the car to a diagnostic shop…where are you located ??
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A dealership couldn’t diagnose a misfire ??…that’s pitiful !!….are these long tube headers ??…sometimes these can cause O2 issues being that they are placed further back in the exhaust stream…are these misfires you can actually feel ??…you are better off taking the car to a diagnostic shop…where are you located ??
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Try posting in the Southwest regional discussion area of the Forum for a good diag shop in your area…or even a Corvette club in your area !!..did you do the header install yourself ??…any exhaust leak upstream of the front O2 sensor would cause a lean condition…these days instead of using a smoke machine I use a shop vac and blow air into the exhaust using a soapy water solution to look for a leak !!
Last edited by C5 Diag; Jul 6, 2021 at 10:12 PM.
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How are you determining you have a misfire? Adding headers, especially mids wont cause a misfire. Something could be up with the plug wires not double clicked onto the coils. They click once onto the plugs and twice on the coils. As for a tuner, if you're into remote tuning there are plenty of tuners on here that can tune the car and are trustworthy. I'm one of them but there are guys on here that are even more experienced than I am. You would need your own HPTuners cable and software though to be able to read and write the tunes.
It COULD be a coil pack failing but it doesn't make sense that a coil would go bad after a header install. It is still far more likely there is an issue with plug wires. I would buy the MSD plug wires and replace the factory ones. I use the MSD's for all the cars I tune and have yet to have an issue.
It COULD be a coil pack failing but it doesn't make sense that a coil would go bad after a header install. It is still far more likely there is an issue with plug wires. I would buy the MSD plug wires and replace the factory ones. I use the MSD's for all the cars I tune and have yet to have an issue.