I have a problem with compression on my '91 305 TPI engine. I have good compression on all 8 cylinders with no spark. However, with spark, I lose compression on no. 1 cylinder. I checked the injector, and it's ok. Any idea's?

 

Totally unrelated. What do you mean with and without spark? Compression is completely mechanical.

 

Typical compression test by disconnecting coil, and turning over the engine results in good compression on all eight cylinders. Reconnecting coil, and starting the engine results in losing compression in no. 1 cylinder. ??????????????

 

How do you know you're losing compression in cyl 1 if the engine is running?
Spark or no spark will not affect compression numbers.

 

Please explain. I'm a little confused about your analysis, too. Then again, it often doesn't take a lot to confuse me...

EDIT:

Typical compression testing should be performed by disabling (not just disconnecting) the ignition coil, removing all spark plugs, blocking the throttle plates open, and cranking with a fully charged battery until peak compression pressure is achieved.

Are you talking about a power balance test instead of compression when running the engine?

 

not that i understand your method of testing.... but a bad piston ring would cause that