I recently completed a compression check on my 1976 280z It's all original from what I was told when I bought the car...

Engine Has 103xxx Miles on it... and the Last 3xxx I have driven. It hasn't had any major issues in the past that I am aware of, but I did have to reseal the fuel tank and clean out and replace a few fuel Injectors.

Results:

Cylinder Pressure

..............(Dry).....(Wet)

1 ... 130 ... 140

2 ... 120 ... 130

3 ... 80 ... 90

4 ... 110 ... 120

5 ... 120 ... 130

6 ... 110 ... 120

I don't Know what the pressure should be but, I'm pretty sure 80/90 on one cylinder isn't right. The car accelerates kind of slow and always has(its an old automatic transmission never really expected anything super amazing). It tops out at about 35/40mph(which isn't right I was getting to 70 on the highways before this issue). And It makes a Metallic clicking sound once it hits 3000-4000rpm.

Any help or advice would be appreciated.

Run a leak down test and see what the results are. Have you run your valves before (valve lash)?

IT looks more like it is in your valves. Good job on running the wet and dry test. THe rings would seem to indicate fine with your tests. I would definitely look on the top end for a culprit.

Yeah, definitely adjust your valve lash. That could be the problem. FAIW, my 280 was 100% dealer serviced for the 15 years prior to my owning it, and I had a few valves that were too tight. I don't know whether that comes from too infrequently adjusted valve lash (i.e. not keeping up with valve seat wear), or whether it comes from too aggressive adjustments in an ill-motivated attempt to completely silence the clicky tappets.

Sarah, you did have the throttle pryed wide open during test?( I know I shouldn't ask this with you, but just checking:))

Valve lash is wear I would go first.

I don't think I tested my compression until well after I adjusted the valve lash. (I had misplaced my gauge.) However, when I did eventually test my compression (approx 185 +/- 5, straight across), it was indeed with the throttle open.

But this is a valid point. Toti, was your throttle propped open for the test? (A closed throttle is a common error.) If not, your pressures might be reading a bit low, although that certainly wouldn't account for the one cylinder that's off.