1998 Grand Prix 3800 NA. 130k miles Dad's car.

I'm no mechanic but here's what I have.

Compression - #1 is 45lbs. #3 and #5 are 175lbs.
Leak down at TDC - #1, pressure seems to flow right out the exhaust, no leakage into #3, no pressure spike in coolant, no air out the dipstick.

Valve lash on #1 was very similar to the rest, indicating to me that the valve might be fully closed and not hanging on carbon or something. I haven't yet measure the valve stem height or valve guide play though.

Am I looking at pulling the heads and having them worked? Or is there something else I should be looking at first?

Thanks in advance for any input.

Ian

Some back up info.....
It developed a miss that would come and go. CEL would light solid and go away after time. Most times it would run fine, but occasionally it would develop a miss while at highway speed and it would stay, from idle right on up. The only code was P0300 misfire. Dad tried chasing the problem down with coils, plugs and wires. It was fine for a while, then the miss came back and stayed for good. CEL started blinking, codes are P0300 and P0301 (misfire in Cylinder #1).

Previously, when chasing the problem and changing plugs, they all looked lean. Now they're all lean and #1 is black with gunk.

Edit: added info

injectors *might* be causing you're misfires. but the low compression could also contribute to misfires, these problems could very likely be tied to each other.

*missed the part about it flowing right out the exhaust.* are you sure you're exhaust valve is closing at the right time? I dont think there is much else you could test other than what you've already done. You're going to have to remove the heads to figure this out.

Try this. Put some thick oil in the cylinder rotate a time or two (without firing) and recheck the pressure. If the pressure comes up you have ring/piston/block issue. If the pressure stays the same you have a head issue. Either way looks like the head will have to come off.