Compression test Lesson

[Ccmano]

So... shortly after I bought my latest 90' Z in June I bought a new compression tester kit at Harbor Freight. I already had one an old one, a Sun Equipment brand, but I wanted one with a check valve and pressure relief. I always had good luck with the Harbor Freight stuff so I got one of their better kits.

I tested the compression on the new Z shortly after I got it and found the readings around 150lbs but steady across all cylinders. While not happy about the readings I was not surprised as the car has 180k miles and I'm at almost 5000ft altitude.

LGAFF suggested I do some intake de-carbonizing and possibly it should pick up some compression. So to start I did 2 rounds of Sea Foam spray directly into the intake. Thought it felt better afterwards.

Today I decided to run another compression test and see what if anything happened. Last time with the new tester I had trouble getting the fitting seated in the #8 cylinder. So I decided to start with #8 and use my old tester that has a slimmer hose. Ran the test and was shocked to get a reading of 195! Hmmm... so I ran #7 with both testers. 195 with the Sun tester, 150 with the Harbor Freight? Ended up running all the cylinders both ways and got the same result. The Sun tester has all cylinders in the 190 to 195 range and the Harbor Freight in the 145 to 150 range.

The old Sun tester has always been accurate. So I got on the Harbor Freight web site and checked the reviews for the compression tester. Guess what, numerous complaints about the testers running 20 - 40 lbs low. One guy even rebuilt his snow mobile engine only to find out the tester was wrong.

So tomorrow the tester goes back to Harbor Freight, I'll stop a Summit Racing down the street and pick a new one with the features I want. And... most importantly I'm jazzed that my 180k mile Z has surprisingly good compression. 195 corrected for altitude puts it in the 210 to 215 range at sea level.

As for Harbor Freight, still good for hand tools, some specialty tools and supplies. Probably not so good for the more sophisticated stuff. If you can call a compression tester sophisticated... lesson learned.
H