please help me troubleahoot my misfire
08-20-2013, 06:29 PM
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please help me troubleahoot my misfire Hi Guys,
Last weekend, I purchased a LS1 Swapped FD from a guy who’s been working on it for about 5-6 years now. I bought it, knowing it still needed some work but the swap was complete and the engine running. When I test drove the car at his place, it ran fine. I trailered it home (6 hours away) and the next day test drove it around my own place and it was struggling VERY hard. Misfiring like crazy under load. I pulled the plugs, and noticed that all the plugs on the passenger side were BLACK. Very Black. I connected a hand held scanner (some crappy one) and noticed that one of the O2 sensors wasn’t doing too much while the other one was fluctuating in voltage. I replaced both sensors with Denso 234-4025’s (the guy had 2 different ones in there for some reason). I also replaced all the plugs to TR55’s gapped at 0.50” (He had bosch platinum plus gapped at 0.35”). Went for a spin, and was getting my hopes up that the issue had gone away. It seems like it has improved, BUT there is definitely still misses under heavier load. BTW – Reason I thought/think it’s an O2 sensor issue is because when the car is cold (Open Loop) the issue doesn’t seem to exist. When it warms up (Close Loop), it happens.
Some history/details on the engine:
1998 Firebird LS1
Fast 102 Intake Manifold & TB
Hinson Long Tube Headers
Cold Air Intake (Hot air if you ask me, since it sits in the engine bay lol)
PCM and harness was purchased from Hotwire Auto. Apparently, the guy ordered the PCM to be tuned for the above setup.
It’s strange to me that the engine is a 98 and the PCM has a sticker “must be used for 1999-2002 LS1 only”. I asked him about this, and he said the custom harness and PCM both came from Hotwire Auto who asked him a bunch of questions and made this for him.
My Theory: (before I continue troubleshooting ignition/fuel)
I don’t think the PCM was programmed correctly. It even throws a Skip Shift code. I’m wondering if Hotwire Auto potentially didn’t delete the downstream o2 sensors, that would have this effect? Or perhaps just a bad tune? I’m going to order an HP Tuner, but before I do, is there any other scanners I can use to help me with troubleshooting this?
Car is hot right now, and I’m back at work. I’m going to pull plugs again from the passenger side. If they’re black again, what else can I start looking at?
Any suggestions and/or ideas would be much appreciated guys. There is a track event this Friday I’d like to try to sort this out for, but if not, a few weeks from now. No worries.
Thanks,
Houman
Last weekend, I purchased a LS1 Swapped FD from a guy who’s been working on it for about 5-6 years now. I bought it, knowing it still needed some work but the swap was complete and the engine running. When I test drove the car at his place, it ran fine. I trailered it home (6 hours away) and the next day test drove it around my own place and it was struggling VERY hard. Misfiring like crazy under load. I pulled the plugs, and noticed that all the plugs on the passenger side were BLACK. Very Black. I connected a hand held scanner (some crappy one) and noticed that one of the O2 sensors wasn’t doing too much while the other one was fluctuating in voltage. I replaced both sensors with Denso 234-4025’s (the guy had 2 different ones in there for some reason). I also replaced all the plugs to TR55’s gapped at 0.50” (He had bosch platinum plus gapped at 0.35”). Went for a spin, and was getting my hopes up that the issue had gone away. It seems like it has improved, BUT there is definitely still misses under heavier load. BTW – Reason I thought/think it’s an O2 sensor issue is because when the car is cold (Open Loop) the issue doesn’t seem to exist. When it warms up (Close Loop), it happens.
Some history/details on the engine:
1998 Firebird LS1
Fast 102 Intake Manifold & TB
Hinson Long Tube Headers
Cold Air Intake (Hot air if you ask me, since it sits in the engine bay lol)
PCM and harness was purchased from Hotwire Auto. Apparently, the guy ordered the PCM to be tuned for the above setup.
It’s strange to me that the engine is a 98 and the PCM has a sticker “must be used for 1999-2002 LS1 only”. I asked him about this, and he said the custom harness and PCM both came from Hotwire Auto who asked him a bunch of questions and made this for him.
My Theory: (before I continue troubleshooting ignition/fuel)
I don’t think the PCM was programmed correctly. It even throws a Skip Shift code. I’m wondering if Hotwire Auto potentially didn’t delete the downstream o2 sensors, that would have this effect? Or perhaps just a bad tune? I’m going to order an HP Tuner, but before I do, is there any other scanners I can use to help me with troubleshooting this?
Car is hot right now, and I’m back at work. I’m going to pull plugs again from the passenger side. If they’re black again, what else can I start looking at?
Any suggestions and/or ideas would be much appreciated guys. There is a track event this Friday I’d like to try to sort this out for, but if not, a few weeks from now. No worries.
Thanks,
Houman
Last edited by houmack; 08-20-2013 at 06:33 PM. Reason: reromat
08-20-2013, 06:35 PM
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after driving it for 10-15 minutes post plug/o2s change, it's back to not being very good. If i'm anything more than 1/4 throttle load, it just misfires like mad. Still seem to only happen, or best worst during, closed loop.