2011 LS9 checking LS9 intake and exhaust lift
02-20-2024, 08:12 PM
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2011 LS9 checking LS9 intake and exhaust lift Hi Folks,
No, I'm not going to ask you to fix this for me, but I am stuck on something, and I'm looking for help. 2011 Silverado 1500 with an LS9. About 170K miles. P0303, I believe it is, random misfires. Looking at my scan tool, I see it's only 1,3 and 7 that's misfiring. None of the others. Compression checks ok, and I moved coil packs and leads around to make sure that's not it, and it's not. No change. I wondered if, since it was only on bank 1, maybe I had an injector problem, or clogged up fuel rail, or something of that nature, so I took rail off, it's clean, and I swapped injectors just to check (1 for 2, 3 for 4, etc), no change. Still misfiring on 1,3 and 7 only. So, since everyone and their brother has started threads like this, and everyone always says cams and / or lifters, I checked that. I didn't want to believe it was valve train, because when the engine runs, it runs silently. No valve clatter at all. No ticking (like my Dodge), no nothing. Just runs nice and quiet. Misfiring away, with that code. Scan tool also says open loop, and O2 sensor waveforms for bank 1 are all over the place. But I'm thinking I'm just going to ignore that because O2 sensors wouldn't cause misfires, right? Misfires would cause O2 sensors to go nuts, I'm thinking. I did replace all 4 sensors though, and CKP sensor as well, just to be on the safe side. Did the relearn a few times too. So I'm back to valve train. According to this site:
Chevy LC9 Engine Specs · Help Center
The lift for intake and exhaust valves should be .481". I checked this engine with a dial indicator held as parallel and inline with the valve stems as possible. I rolled the engine over by hand (wrench at crank bolt), and I didn't get anywhere near that. For instance, on cyl 1 I got .420 and .415 for intake and exhaust. With a hydraulic lifter, how am I supposed to check that spec? I cranked the engine with the starter, until oil pressure builds, and checked it right after that, and got those readings. With the dial indicator at it's highest reading, I can watch it go down as the lifter empties, and I while I watch, I can lose .020, 030, 040". So, how is that spec even measurable or valid? For cyl 5, for example, which never misfires, I got .431 and .365 intake and exhaust. These numbers don't add up, it just doesn't make sense to me.
Can someone help me make sense of it?
Much appreciated.
No, I'm not going to ask you to fix this for me, but I am stuck on something, and I'm looking for help. 2011 Silverado 1500 with an LS9. About 170K miles. P0303, I believe it is, random misfires. Looking at my scan tool, I see it's only 1,3 and 7 that's misfiring. None of the others. Compression checks ok, and I moved coil packs and leads around to make sure that's not it, and it's not. No change. I wondered if, since it was only on bank 1, maybe I had an injector problem, or clogged up fuel rail, or something of that nature, so I took rail off, it's clean, and I swapped injectors just to check (1 for 2, 3 for 4, etc), no change. Still misfiring on 1,3 and 7 only. So, since everyone and their brother has started threads like this, and everyone always says cams and / or lifters, I checked that. I didn't want to believe it was valve train, because when the engine runs, it runs silently. No valve clatter at all. No ticking (like my Dodge), no nothing. Just runs nice and quiet. Misfiring away, with that code. Scan tool also says open loop, and O2 sensor waveforms for bank 1 are all over the place. But I'm thinking I'm just going to ignore that because O2 sensors wouldn't cause misfires, right? Misfires would cause O2 sensors to go nuts, I'm thinking. I did replace all 4 sensors though, and CKP sensor as well, just to be on the safe side. Did the relearn a few times too. So I'm back to valve train. According to this site:
Chevy LC9 Engine Specs · Help Center
The lift for intake and exhaust valves should be .481". I checked this engine with a dial indicator held as parallel and inline with the valve stems as possible. I rolled the engine over by hand (wrench at crank bolt), and I didn't get anywhere near that. For instance, on cyl 1 I got .420 and .415 for intake and exhaust. With a hydraulic lifter, how am I supposed to check that spec? I cranked the engine with the starter, until oil pressure builds, and checked it right after that, and got those readings. With the dial indicator at it's highest reading, I can watch it go down as the lifter empties, and I while I watch, I can lose .020, 030, 040". So, how is that spec even measurable or valid? For cyl 5, for example, which never misfires, I got .431 and .365 intake and exhaust. These numbers don't add up, it just doesn't make sense to me.
Can someone help me make sense of it?
Much appreciated.
