I gave the 73 ES a compression test tonight and to me the results seem a little low for a car with 102,000 miles. Mind you that this is a B20F with low compression and lots of emission control junk on it. I've got an 180 PSI B20E in my Amazon now, so maybe my expectations are too high.

The test results are thus:
1 - 120 PSI
2 - 120 PSI
3 - 120 PSI
4 - 120 PSI

Normally I'd be cheered by such even numbers, but my Amazon's 1967 500,000 mile - once rebuilt - B18 gave me compression readings between 135 and 145 PSI.

So... is this normal?

If the engine runs decently, I would just drive it a bit.

I have seen several older engines get better compression when they are properly maintained and exercised. We had a '90 744TI that had uneven compression at 153,000 miles when we got it, but even numbers (and quite good) at 200,000 miles after a dozen 3,300 mile oil changes.

If it runs poorly or fouls plugs, I would investigate further.

Was the throttle fully open when you did the test? I have seen warnings about poor readings if the throttle is closed. I also like to run the test with all the plugs out and a well charged battery so the engine turns over smartly.
--
'96 855R,'64 PV544 driver, '67 P1800 basket case, '95 855, '95 854, the first three are mine, heh, heh, 415,000 miles put on 9 bricks

Is that wet or dry? If dry, what did you get wet?
--
George Downs Bartlesville, Heart of the USA!

well.. that's with the car cranking and without adding oil to the cylinders aside from whatever is in there already.

If you want to know where the blowby is occurring, put a little oil in each
cylinder and try it again. If it comes up substantially, that indicates worn
rings. If it doesn't come up you have either burnt valves or insufficient
valve clearance (which ESPECIALLY in exhaust valves, can lead to burnt valves.)
--
George Downs Bartlesville, Heart of the USA!

I'm with Rhys, those numbers seem a little TOO even.

But really, even is good, and I wouldn't worry about the absolute number unless the motor seems to be suffering from a lot of blow-by.

I once tested the compression in my Dad's ancient and well traveled old 6 cylinder '52 Ford F350 and got readings between 30 and 35 lbs on all cylinders. The starter didn't even slow down for the compressions, it would just sort of spin the motor gently until it softly chuffed to life.
--
'63 PV544 rat rod, '93 Classic 245 + turbo

Well, I did round the numbers a bit.

The actuals were more like 119, 121, 118, 122. They were all within a couple of psi of 120, so I didn't get too anal on it.

The compression tester I have is a dial gauge contraption with a compressed air type of fitting. and not the most accurate thing in the world, but has been fairly reliable on my previous engine compression tests - save some weirdness with the B20E's #4 cylinder.

The FI cars hide blowby a lot better than the carb-equipped ones. Check it wet and see what's what. Maybe clean up the PCV and EGR systems, they're probably pretty gunked up. That might help bring up your dry reading a couple PSI.

But yeah, until it starts to use a lot of oil AND it's down to 110psi or so, the engine is probably healthy enough.
--
'66 122s, '70 142s, '74 142e... Blue is beautiful.

The only important thing is that they are even. Yours seem almost too even. Nonetheless, I wouldn't be concerned. What the test shows is not an actual value per cylinder, but that all cylinders are the same. When one is not, then that cylinder is suspect for broken or stuck compression rings, or valve seating.