Sounds like the numbers are coming up as engine RPM increases.  That might explain why it runs well, with bad cylinder pressures.  You probably have lots of blowby.

If you have all of the plugs out and the throttle open and a fully charged battery for the most recent test, the only way you could get a little more RPM to bump the numbers up even more might be to connect jumper cables from a running car, to get 14 volts to the starter, instead of 12.6.  But it all seems moot, cylinders 1 and 2 aren't sealing well for some reason.  Also helps explain why it "likes" a higher idle speed.

You might put it all back together and give it a good "Italian tuneup".  Go beat the heck out of it on the road.  Then see if the numbers get better.  

Overall though, it looks like you're in the situation I was in when I got my car.  An old worn engine that runs okay but could be better.  You might have to live with its flaws until you decide to rebuild or swap a new engine in.

On the remote starter, just remember that all you're doing is supplying the small terminal on the solenoid with battery power.  Power to the solenoid small terminal is all you need.  One wire will do it.  My remote starter is a piece of wire with a female terminal on one end, to connect to the solenoid, and a bare end to touch to the battery positive on the other.  It's kind of sparky.

3 hours ago, Geoff's 240z said:

AK260, thanks for the support! Got back in the saddle today with new tool, and also increased starter time from 3-4 seconds per cylinder to ~10 seconds per cylinder to test. Here are the results:

1. 110
2. 125
3. 160
4. 155
5. 140
6. 160

So, feeling much better about things but still have something to investigate in cylinders 1 and 2. Any concern about cylinder 5? 

Lastly, bought a remote starter but wanted to make sure I hooked up correctly. Can you guys confirm? First, connect one cable to the smaller wire connection on the solenoid, then connect to the bolt on the solenoid that connects the positive battery cable. Do I need to disconnect any cables or can just bite onto those connections?

Thanks!

 If you started the compression test with #1, #1 and #2 may be reading lower because the engine didn't have any oil pressure at first. When I start with #1 and test them all, I usually go back and retest #1 and #2 again and usually find the compression has gone up. Did you reset the valves before the latest test?

On 11/18/2018 at 12:51 PM, Geoff's 240z said:

Tested Cold/Warm

1. 60 / 70
2. 60 / 70
3. 100 / 120
4. 110 / 115
5. 90 / 100
6. 115 / 115

 

His first set of measurements seem to show some increase on the second one, but not near the difference between cylinders.  Are we over-hoping?  

40 minutes ago, Zed Head said:

His first set of measurements seem to show some increase on the second one, but not near the difference between cylinders.  Are we over-hoping?  

1

Over hoping? Yup. Just the Pollyanna in me. But the realist in me would be pulling the valve cover, taking a good look at the cam and valve train. Adjusting the valves and retesting.

2 hours ago, Mark Maras said:

Over hoping? Yup. Just the Pollyanna in me. But the realist in me would be pulling the valve cover, taking a good look at the cam and valve train. Adjusting the valves and retesting.

Agree.  The whole engine really needs a good checking.  Obviously it's got problems.  If there's one there might be others.  Best start with the basics and run through the list.

I'm on the same page with you guys. My brother is an accomplished mechanic, but new to the Z world. We'll crack it open over this holiday period and I'll report back. Thanks again for everyone who helped out.

Good luck and here's to hoping it's not serious.

Hi guys, checking in with an update. I had Al at Sparks Performance in San Clemente take a look. He confirmed our compression test results, and used the oil in the cylinder trick to rule out ring issues.

He pulled the valve cover and completed a valve adjustment. The PO had the clearances way too tight. The adjustment helped the numbers considerably...

Al's first test / after valve adjustment

1. 118 / 127
2. 123 / 145
3. 180 / 195
4. 165 / 185
5. 148 / 175
6. 170 / 193

The car performs much better now, including holding its idle without issue. Still, I'll need to have the head pulled and reworked to solve the issues in 1 & 2. As it is driving much better and I'm not longing for a repair bill, I think I'll hold off on head work and cam replacement for a little while.  

Excellent progress