Misfire After Header Install
Thread Starter
Melting Slicks
Joined: Nov 2014
Posts: 2,204
Likes: 17
From: Fayetteville North Carolina
St. Jude Donor '15
Misfire After Header Install
Does anyone know a way to diagnose a bad O2 sensor, I think I have one causing a P0300 but I don't know how to figure out which bank?
I installed my catless ARH mid lengths on Saturday and when I start the car it runs/idles/revs up just fine. After a couple minutes of running it will start to idle really rough and stumble when driving with a flashing CEL.
I took the plugs out when doing the headers and didn't drop any so I don't think they're cracked, I double checked all the pigtails to make sure they're plugged in correctly, and it runs fine when cold it seems like when it goes into closed loop is when it misfires so I don't think it's a loose or bad plug wire or a bad coil.
The only scan tool I have is a diablo Intune. I only drove the car twice, once was home from a friends house (he had a lift) and then once around the block after adjusting the pipes. I cleared the P0300 that showed up on my way home, and when I went around the block and it still ran crappy and the CEL light was flashing I got home and there were no DTC's
I am thinking bad O2 sensor, can removing them with an impact wrench ruin them? Anybody else have other ideas on what to check? Only other mods are AFE CAI, no tune.
I installed my catless ARH mid lengths on Saturday and when I start the car it runs/idles/revs up just fine. After a couple minutes of running it will start to idle really rough and stumble when driving with a flashing CEL.
I took the plugs out when doing the headers and didn't drop any so I don't think they're cracked, I double checked all the pigtails to make sure they're plugged in correctly, and it runs fine when cold it seems like when it goes into closed loop is when it misfires so I don't think it's a loose or bad plug wire or a bad coil.
The only scan tool I have is a diablo Intune. I only drove the car twice, once was home from a friends house (he had a lift) and then once around the block after adjusting the pipes. I cleared the P0300 that showed up on my way home, and when I went around the block and it still ran crappy and the CEL light was flashing I got home and there were no DTC's
I am thinking bad O2 sensor, can removing them with an impact wrench ruin them? Anybody else have other ideas on what to check? Only other mods are AFE CAI, no tune.
Drifting
Joined: Jan 2005
Posts: 1,556
Likes: 276
From: Marshall Texas
You need to call ARH support and they will help straighten you out. I'm thinking you'll have to have it tuned because of a catless connection pipe. ARN # 866-982-1978
Also the AFE could make the car run lean without a tune??
Also the AFE could make the car run lean without a tune??
Thread Starter
Melting Slicks
Joined: Nov 2014
Posts: 2,204
Likes: 17
From: Fayetteville North Carolina
St. Jude Donor '15
I asked before I purchased and ARH specifically told me that mid lengths would not require a tune, even with a CAI.
The question of running lean is really independent of a misfire/rough idle/P0300 code.
Burning Brakes
Joined: Jan 2014
Posts: 1,078
Likes: 262
From: swoyersville pa
I just talked about this yesterday, there is going to be a tent at corvette of Carlisle in two weeks selling/installing headers at the show, I was told to pay the extra $200 right then for the retune or I will be towing it to tuner sooner than I think.
Team Owner
Joined: Jan 2007
Posts: 29,063
Likes: 1,839
From: cookeville tennessee
Car will not run with out the cat unless it is retuned. I just put headers on my car but with the cat's but I put LG LT headers. The guy they told me to get the cat are will have to be tuned with out them in the car. These c7 are not like the c5...
now get this I had a friend helping me and he PUT THE 02 SENORS IN BEHIND THE CAT'S & MY CAR DID THE VERY SAME THING THAT YOU ARE SAYING HERE. It was good for just a few until go a little warm then same as what you say your car is doing.
I put my car back on my 4 post lift saw what he had done & pulled them out and put them in front of the cat's the car did just fine then.Robert
Thread Starter
Melting Slicks
Joined: Nov 2014
Posts: 2,204
Likes: 17
From: Fayetteville North Carolina
St. Jude Donor '15
Car will not run with out the cat unless it is retuned. I just put headers on my car but with the cat's but I put LG LT headers. The guy they told me to get the cat are will have to be tuned with out them in the car. These c7 are not like the c5...now get this I had a friend helping me and he PUT THE 02 SENORS IN BEHIND THE CAT'S & MY CAR DID THE VERY SAME THING THAT YOU ARE SAYING HERE. It was good for just a few until go a little warm then same as what you say your car is doing.
I put my car back on my 4 post lift saw what he had done & pulled them out and put them in front of the cat's the car did just fine then.Robert
I have a diablo Intune I can try loading a tune but I really didn't want to tune my car if I didn't have to.
I'm surprised that no cats would cause it to stumble so hard it can barely go down the road and idle rough and flash the CEL...
EDIT: The front O2's are in front of the cats anyway, so why would removing the cats affect their reading?
Last edited by 10mm_; Aug 17, 2015 at 10:41 AM.
Thread Starter
Melting Slicks
Joined: Nov 2014
Posts: 2,204
Likes: 17
From: Fayetteville North Carolina
St. Jude Donor '15
And I was told by the company that makes these headers that I wouldn't need a tune...
Team Owner
Joined: Jan 2007
Posts: 29,063
Likes: 1,839
From: cookeville tennessee
I still have all 4 O2 sensors and I still have my rear cats, I put all the senors back in the location they go except I used the included extensions for the rear sensors.
I have a diablo Intune I can try loading a tune but I really didn't want to tune my car if I didn't have to.
I'm surprised that no cats would cause it to stumble so hard it can barely go down the road and idle rough and flash the CEL...
I have a diablo Intune I can try loading a tune but I really didn't want to tune my car if I didn't have to.
I'm surprised that no cats would cause it to stumble so hard it can barely go down the road and idle rough and flash the CEL...
Plus before car being stock it was running JUST a little rich by the plugs. Now with the LT headers & cold air box on it by the plus looks good by old school looking of the plug.
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Thread Starter
Melting Slicks
Joined: Nov 2014
Posts: 2,204
Likes: 17
From: Fayetteville North Carolina
St. Jude Donor '15
I mean 99% of the time removing a cat will get you a catalyst efficiency code, I don't have one of those.
I'm going to use the intune to data log misfires and O2 voltage after work, hopefully I see something in the log that points me in the right direction.
Thread Starter
Melting Slicks
Joined: Nov 2014
Posts: 2,204
Likes: 17
From: Fayetteville North Carolina
St. Jude Donor '15
Another weird thing it does is that it will misfire and barely move down the road, then the CEL starts flashing and it smooths out and runs about normal. It's like the flashing CEL doesn't indicate the misfire until it stops misfiring. Maybe that's some kind of safety mode or something.
After that test drive I pulled the codes and there were none. It was a very short drive though.
Instructor
Joined: Sep 2014
Posts: 224
Likes: 2
Sounds ignition related. Plug wires are most likely the culprit. My stock plug wires are basically shot when i pulled them off. Try wrapping the plug connectors under the metal head shields on the wires with electrical tape and reinstalling. If this works your plug wires are shot and arcing the spark onto the new headers. Also be sure that you do not have any dielectric grease on the actual metal connections.
Thread Starter
Melting Slicks
Joined: Nov 2014
Posts: 2,204
Likes: 17
From: Fayetteville North Carolina
St. Jude Donor '15
Sounds ignition related. Plug wires are most likely the culprit. My stock plug wires are basically shot when i pulled them off. Try wrapping the plug connectors under the metal head shields on the wires with electrical tape and reinstalling. If this works your plug wires are shot and arcing the spark onto the new headers. Also be sure that you do not have any dielectric grease on the actual metal connections.
Instructor
Joined: Sep 2014
Posts: 224
Likes: 2
No, when they get hot the silicone that shields the wires is not as effective, especially if you have a cut or pinhole in the connectors. My stock wires were also loaded up with dielectric grease on the actual connector themselves which is exactly where you do not want it to be lol.
Team Owner
Joined: Jan 2007
Posts: 29,063
Likes: 1,839
From: cookeville tennessee
Team Owner
Joined: Jan 2007
Posts: 29,063
Likes: 1,839
From: cookeville tennessee
Wouldn't that be for a P0420 code? This isn't for a CEL because I have no cats, this is a really bad misfire / dramatic loss of power.
Another weird thing it does is that it will misfire and barely move down the road, then the CEL starts flashing and it smooths out and runs about normal. It's like the flashing CEL doesn't indicate the misfire until it stops misfiring. Maybe that's some kind of safety mode or something.
After that test drive I pulled the codes and there were none. It was a very short drive though.
Another weird thing it does is that it will misfire and barely move down the road, then the CEL starts flashing and it smooths out and runs about normal. It's like the flashing CEL doesn't indicate the misfire until it stops misfiring. Maybe that's some kind of safety mode or something.
After that test drive I pulled the codes and there were none. It was a very short drive though.
Plus I called LG & the guy told me if I ran no cat at all these cars now will have to be tuned for that and the rear one'e will have to be turned off to get the check engine line to go off. From LG that is the only reason I paid extra for the front cat;s for the car for now.. Robert
Team Owner
Joined: Jan 2007
Posts: 29,063
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From: cookeville tennessee
But I still think my car is in need of some small tuning on it now.
Supporting Vendor
Joined: Sep 2009
Posts: 2,143
Likes: 169
From: Central Florida
You've moved the O2s downstream, hence the misfires, not uncommon after a header install.
Often the min rpm to enable misfire monitor needs to be bumped a bit assuming there are no small leaks, etc.
Thanks
Often the min rpm to enable misfire monitor needs to be bumped a bit assuming there are no small leaks, etc.
Thanks