2007 Trailblazer v8 misfire under load?
06-13-2020, 08:56 PM
#1
2007 Trailblazer v8 misfire under load? So was driving home from work today, cruising at 70 mph. About 10 miles or so from the house, MIL starts flashing. I was In the middle of an incredible rainstorm so I kept driving. Hit some traffic due to the rainstorm, decelerated to about 20 mph and just rolled for a while. MIL Stopped flashing. Made it through the rain and got back up to about 50, MIL starts flashing again. Get off the freeway and as soon as I return to idle the MIL turns off. Cruise back home at 30 and it stays off.
In the driveway I revved the motor a little bit in park, find that it's misfiring pretty heavily from 1100 rpms to about 1700. Haven't scanned for any codes yet, but I'm wondering if anyone might have any ideas. Only mod to the motor is a ported throttle body. I still have a stock one laying around so I'll swap that out as soon as the rain lets up. Didn't hear any unhappy noises either, but it was difficult to hear anything over the rain.
Any thoughts on where to start? Going to pull codes here in a bit, but just curious if anyone knows of any common issues I might start with, and/or if the TB is a likelihood.
In the driveway I revved the motor a little bit in park, find that it's misfiring pretty heavily from 1100 rpms to about 1700. Haven't scanned for any codes yet, but I'm wondering if anyone might have any ideas. Only mod to the motor is a ported throttle body. I still have a stock one laying around so I'll swap that out as soon as the rain lets up. Didn't hear any unhappy noises either, but it was difficult to hear anything over the rain.
Any thoughts on where to start? Going to pull codes here in a bit, but just curious if anyone knows of any common issues I might start with, and/or if the TB is a likelihood.
06-13-2020, 09:45 PM
#2
So to make things even more difficult... Went out with my HPTuners and read codes. P0300 and P0301, not really surprised there. There was an old code about a throttle position sensor circuit out of range, but I'm pretty sure that's like a year and a half old.
Started the truck and logged misfires for all 8 cylinders, both current and the history. History shows something like 33k misfires for Cyl 1 (and 20-90 for the rest of the cylinders). Let the truck idle to come back to temp and started revving it up to 2k. Barely a hiccup. Scanner showed a couple of misfires on Cyl 1, but nothing significant.
What sounds likely here for something that's apparently intermittent? Spark plugs were replaced almost 2 years ago, and have maybe 20k-ish on them (Were ACDelco platinums, I believe). Injector? Coil? Never heard any unhappy noises so I'm not thinking it's valvetrain related...
Started the truck and logged misfires for all 8 cylinders, both current and the history. History shows something like 33k misfires for Cyl 1 (and 20-90 for the rest of the cylinders). Let the truck idle to come back to temp and started revving it up to 2k. Barely a hiccup. Scanner showed a couple of misfires on Cyl 1, but nothing significant.
What sounds likely here for something that's apparently intermittent? Spark plugs were replaced almost 2 years ago, and have maybe 20k-ish on them (Were ACDelco platinums, I believe). Injector? Coil? Never heard any unhappy noises so I'm not thinking it's valvetrain related...