My compression test was between 155 and 170 is this unusual? Is this high? The mpg dropped 1.5 years ago, The car'* mpg was good for the first 4.5 years. I have a borescope can I look through the spark plug hole and see damage?

Should I crank the engine with no spark and then pull the plugs to see what is on the plugs? I have not done the lower intake manifold gaskets. I can tell the upper manifold has a date code of 2005, so I know someone did the upper.

It depends on what the specs are for this engine. I used to have a 95 FSM, but no longer. If you get onto Alldatadiy.com and pay for a 1 year subscription, you can get rebuild specs and a bunch of other good stuff.

Typically, when MPG starts to drop, its an indication that hard parts are starting to wear out. This is typical after everything else has been replaced and gone over including tires, any additional weight added to the vehicle, even a dirty car can drop MPG.

If there was enough physical damage to the inside to the point a borescope would see it, you would have far more issues than a drop in MPG.

200,000+ miles is enough evidence to show a drop in MPG. At this point, one can only deal with it, or bite the bullet and have the engine rebuilt. If the body is in great shape, I suggest buying a reman engine that comes with a WARRANTY. Even if you put it in yourself, the warranty is still valid. If you have national chain like a dealer do it, the labor is also covered nationwide.

Body is in good shape. Not worth an engine swap. Spec compression ratio is 9.4, so if my gauge is accurate, I'm at 11 to 11.7. I'll try someone else'* gauge first. No smoke out the exhaust. I understand the borescope is a waste of time.

I meant no gas not no spark and then pull plugs to see if oil or coolant is on them. I will redo the compression test with and without the upstream o2 sensor to rule out restricted cat.

That'* a good idea.