As mentioned above, think valve seals and valve guides first. I had to replace my cam shaft position sensor and my knock sensors plus the knock sensor wire harness. Ditto for a wonky engine coolant temperature sensor. All of this before or shortly after swapping my 150,000 mile 1999 model year LM7 in.

After that, I also picked up random misfires. Tried new spark plugs, new coil packs, new injectors, new plug wires, tried a crank position relearn - all, no help. Finally, I put in a different PCM . . . . haven't had a single misfire in two years or more. This was the absolute last thing that should have been the problem but it was.

Rick

 

valve seals, yes! but guides? I haven't seen too many worn out on LS motors yet

 

Maybe ill look into the crank position relearn just to give it a shot. And ill also try to find a cheap scan tool that i can see live data on.

When i was researching the smoke upon start up, the two common things that came up were clogged PCV and valve seals but not much on valve guides. I guess there is some process for doing a new PCV and modifying it in the valve cover in some shape or form to prevent it from happening again today.

 

All,

just wanted to update and say truck is running great now. It was the intake manifold gasket. I had to do the job twice tho because I over torque it the first time and leaked even worse. Also popped, clean, and re sealed all injectors. No more oil consumption after cleaning out the PCV orfice and modifying it to act like the newer style valve covers. There is a video on YouTube about it that shows it really well.

thanks for all the help

 

Nice! Thanks for the update.

I've actually been able to remove and reuse intake manifold gaskets. I just inspect them to make sure they are not damaged. I believe the Felpro instructions say to use thread locker on the bolts?

Can you please post a link to the mod you are talking about?