Overheating/misfire issue after header install.
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Teching In
Joined: Feb 2014
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From: Tulsa, OK
Overheating/misfire issue after header install. Hey guys, I did a header install this past weekend on my 98 Z28 and now I am having overheating/misfire issues. With the headers I did an EGR/air delete, the TB coolant by-pass, and put in new plugs gapped at .047. I did start It with open headers just to see how it sounded, At that time I didn't have my front O2 sensors extensions yet so they were unplugged. Now I have them plugged in and I have the cats welded on until I can get my 40series put up. But anyhow it runs fine above 2500rpm, when I put it in 6th and try to accelerate the whole car shake super bad and when it starts to get hot (I have not let it into the red I stop it about half way between 235 and red) you can here a backfire, it sounds like the right bank to me. So, any ideas? I have checked the wires and they all appear to be good and snug on the plug and coil. Maybe a fouled plug from no O2 sensors at first? Thanks Guys
You've significantly improved the ability of the engine to move clean air in and out - that's the whole point. Did you increase the ability to add fuel? Overheating is often caused by a lean mixture.
If the 02's weren't hooked up when you started it it was running in open loop. If you had them hooked up and ran it I think there would be a better chance of you fouling a plug because it would have gone in closed loop and the PCM would have done what the 02's were seeing with them being so close to the end of the header.
Are you getting a CEL?
I would disconnect the battery for about ten minutes for the KAM to reset.
I am going to assume you removed the coil packs. Are they plugged in correctly?
I'm pretty sure on 98's you can actually hook them up backwards.
As mentioned if it's over heating when you load the engine in sixth it's running lean. That can be either from not enough fuel or the cylinders firing at the wrong time.
I know 98 PCM's are a breed of their own and I don't know how much extra fuel it can add to the stock tables. I know a lot of people on here who put headers on and drive without getting it tuned and don't have any problems.
Let us know what you figure out.
Are you getting a CEL?
I would disconnect the battery for about ten minutes for the KAM to reset.
I am going to assume you removed the coil packs. Are they plugged in correctly?
I'm pretty sure on 98's you can actually hook them up backwards.
As mentioned if it's over heating when you load the engine in sixth it's running lean. That can be either from not enough fuel or the cylinders firing at the wrong time.
I know 98 PCM's are a breed of their own and I don't know how much extra fuel it can add to the stock tables. I know a lot of people on here who put headers on and drive without getting it tuned and don't have any problems.
Let us know what you figure out.
If the 02's weren't hooked up when you started it it was running in open loop. If you had them hooked up and ran it I think there would be a better chance of you fouling a plug because it would have gone in closed loop and the PCM would have done what the 02's were seeing with them being so close to the end of the header.
Are you getting a CEL?
I would disconnect the battery for about ten minutes for the KAM to reset.
I am going to assume you removed the coil packs. Are they plugged in correctly?
I'm pretty sure on 98's you can actually hook them up backwards.
As mentioned if it's over heating when you load the engine in sixth it's running lean. That can be either from not enough fuel or the cylinders firing at the wrong time.
I know 98 PCM's are a breed of their own and I don't know how much extra fuel it can add to the stock tables. I know a lot of people on here who put headers on and drive without getting it tuned and don't have any problems.
Let us know what you figure out.
Are you getting a CEL?
I would disconnect the battery for about ten minutes for the KAM to reset.
I am going to assume you removed the coil packs. Are they plugged in correctly?
I'm pretty sure on 98's you can actually hook them up backwards.
As mentioned if it's over heating when you load the engine in sixth it's running lean. That can be either from not enough fuel or the cylinders firing at the wrong time.
I know 98 PCM's are a breed of their own and I don't know how much extra fuel it can add to the stock tables. I know a lot of people on here who put headers on and drive without getting it tuned and don't have any problems.
Let us know what you figure out.
Thread Starter
Teching In
Joined: Feb 2014
Posts: 6
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From: Tulsa, OK
No, I was able to do the install without removing the coil packs. All I did was remove the plug wires. I was careful not to pull on the wires themselves just the boots. The only codes I am getting are for the EGR valve and no activity from the rear o2 sensors. I re-checked the cooling system and did the bleed cycle again just to make sure there was no air in it. I didn't think about it being hot because of a lean condition, maybe I snagged a vacuum line somewhere. I will look for a leak tomorrow when I get off work. I don't have any codes for misfire or lean condition either, strange.... But thanks for the input!!
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Thread Starter
Teching In
Joined: Feb 2014
Posts: 6
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From: Tulsa, OK
All right, update. I only have a code reader with freeze frame data. I found a small vacuum leak where the EGR tube goes into the intake. Fixed that, and replaced the sparkplug wires. Also I read that if the temp sensor goes bad it can make it run rough, so I checked that with the freeze frame data from the codes and it is reading correctly. I am stumped..... It was running like a champ before the install. I have been checking the coolant on every startup and it has not been low. Does the LS1 use the knock sensors for misfire detection? I am not sure if they have ever been changed, if they were bad maybe the engine doesn't know it has a misfire.... Thanks guy I really appreciate it.
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Pull your plugs and make sure ya didnt crack one while putting the headers on....assuming ya put new plugs in and than put the new headers on.
If ya put in junk plugs that could be it also, Bosch Platniums are a NO Go
If you didnt let the car run for a bit w the Radiator Cap off after ya did your coolant by pass than you could have air in the system and thats your over heating issue.
Helps to also jack the front of the car up and have it a foot off the ground and let it run w the cap off to get all the air out of the system
If ya put in junk plugs that could be it also, Bosch Platniums are a NO Go
If you didnt let the car run for a bit w the Radiator Cap off after ya did your coolant by pass than you could have air in the system and thats your over heating issue.
Helps to also jack the front of the car up and have it a foot off the ground and let it run w the cap off to get all the air out of the system
Last edited by 1999Firehawkls7; Mar 19, 2014 at 11:41 PM.
Thread Starter
Teching In
Joined: Feb 2014
Posts: 6
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From: Tulsa, OK
Yeah, I changed them. The guy at Oreileys said they take double platinum spark plugs. I wanted AC Delco, but all they had was Autolite. I Will put the car up on my ramps and do the bleed cycle again. And when I did the by-pass I didn't take any lines off of the radiator. Can a misfire cause an engine to overheat? Thanks
Thread Starter
Teching In
Joined: Feb 2014
Posts: 6
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From: Tulsa, OK
All right, I got ahold of the fuel trim. STFT B1 -2.34%, LTFT B1 17.97%, STFT B2-1.56%, LTFT B2 17.97%. Also, I put the car on ramps and did the bleed cycle again and when it starts to get hot bubbles start to come out of the fill hole. It also started to push the coolant out of the fill hole after it got hot. Is that just steam? Thanks
