In the event a nissan vg30e engine has 110 psi compression in a cylinder where the engine runs rough and misfires, would it be ideal to run it as is or disabling fuel and spark on that bad piston and its mirror piston?

Running an engine with a cylinder that has only 110 psi of compression can lead to several issues, including rough running, poor performance, and potential further damage to the engine. A compression reading of 110 psi is generally considered low for a VG30E engine, which typically should have compression readings in the range of 150-180 psi for healthy cylinders. If you disable fuel and spark on the affected cylinder (and its mirror piston, which would be the corresponding cylinder in a V engine), the engine may run smoother since it won't try to fire that cylinder. However, you're effectively running the engine on fewer cylinders, which could lead to: 1. **Increased load on the remaining cylinders** - This can cause them to wear out faster due to the extra effort they need to put in to compensate for the lost power from the disabled cylinder. 2. **Unbalanced engine vibrations** - Running on fewer cylinders can lead to rough vibrations, which might not be ideal for the longevity of the engine mounts and overall engine balance. 3. **Fuel economy and emissions** - Running an engine this way can lead to poor fuel economy and potentially higher emissions, which may not be compliant with regulations in your area. 4. **Additional Diagnostic Attention Needed** - It's most important to address the underlying cause of low compression, which could be due to things like worn piston rings, a blown head gasket, or valve issues. In conclusion, while you can disable fuel and spark to the affected cylinder for temporary relief, this is not a sustainable solution. The best course of action would be to diagnose and repair the underlying issue causing the low compression in that cylinder. Running the engine in its current state could lead to further damage over time.