Before replacing the engine, start with the simplest things first. Has this been a problem that has come on fairly quickly or has it been a slowly growing one? Did it start after say. Buying gasoline at a particular place or delving through a massive mud puddle? Anything unusual happen in the near past?
Things to check first:
A leaking fuel injector will cause the symptoms you describe. It will also wash the cylinder walls down with gas and lower compression significantly. Check the fuel pressure and do a cylinder balance test.
The ignition system will cause the symptoms you describe, but it will only cause low cylinder compression indirectly by an ignition induced misfire allowing unburnt gas to wash down the cylinder walls again. Check the ignition system components to make sure they're all functioning correctly.
A massive vacuum leak will cause the symptoms you describe, but it will not contribute to a low compression reading. Best to check for vacuum leaks to make sure.
If all comes back as functioning correctly, do a compression test. On the cylinders that read lower, squirt some oil into those cylinders and to the test again. If they read normal then suspect bad rings. The oil will temporarily provide the seal the rings aren't providing. Then follow that up with a cylinder leak down test to make absolutely sure.
The cost and time to do all this is small compared to replacing the engine only to find out the problem is still there and the removed engine was fine. Let us know.
Sunday, July 15th, 2007 AT 9:01 PM