Hi all,
I have a 2006 C6Z with a built LS7 with maybe 15k miles on the build. Long story short, a couple of years ago the oil pressure sensor went out, I thought the engine had blown and I parked the car for a while as I didn't have time to deal with it. Over the past year or two I've been trying to bring it back to life. It seems after sitting for some time the intake manifold gaskets were toast as I heard a bad vacuum leak so they've all been replaced, I went ahead and replaced the injectors and fuel rail as well, replaced spark plugs with fresh TR6s, pumped the tank of gas out of it and filled up with fresh gas along with stabilizer. The car idles just fine (for a cammed car anyways) has fine oil pressure etc. It accelerates just fine too no mishaps there. The issue is at constant throttle, so trying to cruise at say 40mph, the car acts like it is misfiring horribly or something of that nature. It jerks around a lot and bucks. I have a fuel pressure gauge and I can measure at least at idle I have a constant 60 psi of fuel pressure along with when I rev it. My gauge's hose is unfortunately not long enough for me to tape it to the window and drive around so I don't know if the fuel pressure dips during load or not. The fact that it accelerates just fine and doesn't stumble there has me not suspecting that as much though. I also haven't touched the coils or plug wires as they're relocated to the fenders and are a PITA to get to. So perhaps those should be next? Any one have any ideas of where to start here or what is going on? I'm confused as to where to look since the problem only manifests itself during constant throttle and not when accelerating or anything. Do I maybe need to retuned? I have HPTuners and an MPVI3 that I can log with if anyone has any ideas of what to look for. Any help or ideas would be appreciated!

 

If you think it's misfiring do you have any misfire DTC's stored ??...it can be something like a flakey Throttle Position Sensor...can you graph your TPS going down the road ??...if the fuel pressure doesn't drop on a snap throttle the fuel pressure is probably OK...what are your O2 sensors and fuel trims doing during this constant cruise ??..below is a graphed TPS1 signal with ignition on with foot to the floor on the accelerator…at constant speed that signal should not be dropping out….same for TPS2…this can also be a flakey crank sensor…find a diagnostic shop in your area that uses a labscope…they can find what’s wrong easily....test...don't guess !!

 

Thank you for the response! I do not have any misfire codes stored when I go and read them and I do not see any misfires when I log and drive around, but perhaps it's just not catching them with the tune I have. Not so sure there. As far as the TPS sensor it doesn't look like it's dropping out at all. I went and did a loop around the block and logged what I could. I kept throttle as constant as I could with the bucking. Doesn't seem to be dropping out at all. I don't know entirely what to expect out of the O2 sensors but they looked about what I would expect from them? Again not too sure what to look for there. The STFT flatlines half way through the constant throttle, not too sure why. Is there a good way to diagnose a flaky crank sensor?

Another constant throttle at ~45mph:

 

The only way to diagnose a crank sensor is with a labscope…below is a crank (blue) and red (cam) sensor on my 08…a digital 0-5 volt square wave.