LQ4 misfire issues
12-04-2011, 03:07 PM
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LQ4 misfire issues My buddy has an 03 Silverado with a bone stock LQ4. It's throwing a P0300 misfire code. I hooked my autotap up to it and we went for a drive.
Under light driving conditions, we'll get the occasional misfire from Cylinder 1 and 6, and heavy misfires from 5 and 8. At a steady 70mph on the highway, they all get worse, and that's when it throws the code. On the highway, 5 and 8, along with 6 and to a lesser extent 1, all misfire constantly. Attached is a screen shot that I took while he was driving at 70mph. The big window shows cylinders 5-8 and the small window shows 1-4.
Does anybody have any suggestions as to what what we should be looking at to diagnose this further? Based on the fact that it's showing misfires on both banks, we don't think it's related to the coils and associated wiring. Right now we're leaning toward thinking that it's the intake gaskets, but we haven't sprayed around it with ether yet to see. The truck seems to idle at a steady 15:1 A/F ratio. I didn't think to check the a/f ratio while we were driving.
Anybody have any ideas for things we should check?
Under light driving conditions, we'll get the occasional misfire from Cylinder 1 and 6, and heavy misfires from 5 and 8. At a steady 70mph on the highway, they all get worse, and that's when it throws the code. On the highway, 5 and 8, along with 6 and to a lesser extent 1, all misfire constantly. Attached is a screen shot that I took while he was driving at 70mph. The big window shows cylinders 5-8 and the small window shows 1-4.
Does anybody have any suggestions as to what what we should be looking at to diagnose this further? Based on the fact that it's showing misfires on both banks, we don't think it's related to the coils and associated wiring. Right now we're leaning toward thinking that it's the intake gaskets, but we haven't sprayed around it with ether yet to see. The truck seems to idle at a steady 15:1 A/F ratio. I didn't think to check the a/f ratio while we were driving.
Anybody have any ideas for things we should check?
12-07-2011, 01:02 AM
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What is the base fuel pressure? I have a buddy who has the same issue which I diaged at work,apparently according to the diagnostic info that issue is pretty common and there's a lot of hits on fuel pumps,he has yet to do it but I believe that's the cause of it.basically whats probly happening is lack of fueling. I am having the same issue on my lq4 swapped camaro same cylinders and all. But check fuel pressure and check the regulator as well those are also common
