They said the cylinders were fine, but I found all the cross-hatch from the factory honing to be gone and replaced with piston skirt and cylinder wear marks and pitting in the area of the piston skirts. They explained that GM determined that in most cases this is the most likely cause for oil consumption, so they did not address those. The kit they specify for this work includes new valve guide seals. Although the special coverage identifies worn valve guides and seals as a source of oil consumption. The did this with the engine still in the vehicle. They replaced both timing chains and guides, even though they replaced them only a few months ago. Replaced the pistons and rings, cleaned PVC port, and replaced necessary gaskets and seals as procedure requires. No problems, no leaks, and performance is about the same. I put about 50 highway miles on it,alternating engines speed every few minutes. ![]() Hope this answers all the above questions. Now that I have the Ultra Gauge, I can watch my intake MAP and fuel trims on those hills. I usually shift down to 5th on hills to keep the rpms up. I am in the midwest so not much affect from altitude. Might be mis-match between the 4 cylinder engine and 6 speed transmission. Not sure it will be fixed with the piston and ring replacement but the engine will easily lug at highway speeds (65-70) in 6th gear on very slight grades. 210-220 psi between all four cylinders and no more than 4-5% leakage. Prior to the work, I had them perform a compression and leakdown on all cylinders. I asked about the cam actuators, and they did not think there was a problem. One exhaust manifold stud had snapped off and missing, or that is what they told me. The GM manifold I looked at was much better but nearly twice the price. I looked at an aftermarket manifold and it was poorly cast, with flaws. The exhaust manifold has crack starting in the normal location. I doubt they measured bore diameter or ring gaps before installing them. I will be going back tomorrow to inspect the cylinders more closely and the pistons. ![]() ![]() The shop also said the head needs to be resurfaced to prevent gasket failure. The machine shop said they see a lot of the clogged from excessive use of RTV. There is a TSB about inferior oil filters that lodge gasket or filter material in the restrictor. Had them clean the oil galley and the restrictor in the head, which fees the cams and VVT. The shop is grinding the exhaust valves, they have a lot of pitting. They looked like a well seasoned iron skillet, jet black and smooth. A lot of varnish, the intake valves and intake runners were baked on black, but not a lot of loose carbon. I sent the head to the machine shop for a complete cleaning. I have an ultra gauge on my car, the voltage levels and CAT temps are good. The cylinder bores show no major scaring, the CAT looks good no heavy contamination, but I could not shine light through it because it was still attached to the pipe. ![]() I will create a separate thread for that and the response from GM. I have been catching a lot oil, water and a little coolant. I installed oil separator on the PCV vent hose between the valve cover and air breather after reading about the freezing slime in the intake causing rear main seals to leak. Two doors repaired the rust using POR 15. Removed the rust from the chassis and underbody, and coated with Fluid Film. New battery, air filter, and cleaned the throttle body. flushed the cooling system, and switched to Amsoil engine oil. I have flushed the transmission and replaced with Amsoil ATF, which resolved hard shifting and noise. I did an oil analysis and confirmed what my nose was telling me. Timing chains and DFI fuel pump replaced. I bought a Route 66 warranty and it has nearly paid off. I did my homework and thanks to your forum I learned about the cam timing chain, PCV, exhaust manifold, door rust, and fuel pump, and oil consumption problems. He started having driveability issues at 76K and so they replaced the cam actuator solenoids, BG intake cleaner, plugs and air filter. The previous owner just did the normal maintenance and no major failures.
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