LACK OF POWER

Nope. Stick with your original question. Ras is answering just about every question that pops up so he's busy but we get automatic e-mails with direct links back to the original question. He will be back when he reads that e-mail. In the unlikely chance he doesn't get back to you soon, check the links on the lower right side under "Engine Performance" or "Engine Mechanical" for directions on performing a compression test. If you don't find anything there, reply back to this post and I'll copy and paste the directions I printed out for my students. There are some tidbits that aren't included in service manuals because the assumption there is you already know what to do.

If the catalytic converter is plugged the engine will idle unusually smoothly and you'll hear more of a hiss from the tail pipe rather than the normal "putt putt". At higher speeds there might be some popping back through the intake. An air filter would have to be really plugged to be noticeable. Remember, it has to be able to pass enough air to let the car go over 100 miles per hour. Hopefully you're only asking it to go half that fast which means about 1/3 as much air and fuel. I don't think this applies to your engine but if it still has a distributor, retarded timing can cause a severe loss of power. A real good clue, if you have the header-type exhaust manifold with thin metal tubes instead of the cast iron manifold, is it will turn orange when the timing is retarded. That's because the fuel is fired too late and finishes burning in the exhaust manifold instead of in the cylinder. Next, check for any air leaks in the fresh air tube between the mass air flow sensor and the throttle body. Also look for vacuum leaks. Any air that sneaks in that doesn't go through the mass air flow sensor won't get measured and the Engine Computer won't command the matching amount of fuel to go with it. Another plan of attack is to use a scanner to view live sensor data while you're driving. Also look at the fuel trim numbers. If they are very high positive or negative, the computer is adding or subtracting a large amount of fuel from the calculated values in an attempt to correct a problem. That problem could be related to low power.

Do you mean half of the cylinders are firing? The module or Engine Computer fires every spark plug so if the engine is running, the computer is working. You would definitely feel a misfire too and the engine would be hard to start.

Do you have four individual coils or two coils in one assembly with four spark plug wires. Two bad individual coils at the same time would not be likely. A single bad coil in a coil pack is somewhat common. That will make two cylinders lose spark. GM coil packs have an electronic module built in that fails. On some of them, the old coils can be unbolted and installed on the replacement module. On some you have to replace the entire assembly.

When you check those for spark, you have to leave one plug wire on. The current goes through the coil, one plug, ground, the other plug, then back to the coil. If both plug wires are removed, you normally won't get a spark from either one.

Okay. First, can you switch the coils to see if the same coil has no spark? If the same cylinders are dead, the list of suspects would be the module, the Engine Computer that fires the module, or you might look at the timing belt. I don't know if this applies to your engine but some engines are shut down by the Engine Computer when the timing belt jumps a few teeth. The computer knows that by the change in relationship of the pulses from the crankshaft position sensor and the camshaft position sensor.