Tunk88

I did a compression test yesterday. Drove the car for about 30mins, parked, and got started. My readings were low, 182 181 180 183. Consistent but low. I'm wondering if the low readings could of been my gauge from harbor freight? My leak down gauge was broke out of the box, but didn't realize until I tested two cylinders. And even with a broke gauge, there wasn't any alarming air leaking noise. Valve retainers were good ( checked the night before) and valves were adjusted (adjusted the night before) Exhaust .011-.012 intake .009-.010. The car idles so well, runs perfect. Pulls hard through entire RPM range. Has anyone ran into this issue? I suspect the engine would show symptoms of such low compression?

2007 AP2 F22c
29,000mi.

Chuck S

Those readings are mid-spec. It's in the service manual. Nominal is 228psi but Minimum is 135psi. 28psi variance between cylinders. Engine turning over at 250rpm (starter motor) with the throttle wide open. Disconnect the fuel pump fuse.

-- Chuck

Tunk88

The fuse was disconnected, all spark plugs removed, WoT, battery hooked up to charger. I didn't realize those numbers are midspec (although I'd like to be at the higher end). The lower numbers scare me a bit. But like I said I wasn't sure if symptoms would show with those numbers.

osu1978

I know I have read somewhere that other people were getting low numbers from the HF gauge across all cylinders. Your figures are very consistent so I would be more worried if 3 cylinders were similar and one was significantly lower.

rmerchant3

The HF gauge is consistent, but reads low. I had one and every s2000 I tested read around what you got. I bought a nice gauge and all my readings went up about 20-30 psi. If you are worried about it, test again with a quality gauge. The HF leakdown reads higher than normal too. It was considered ok if there was a 20% loss with that gauge.

Tunk88

Good to know someone has had some experience with these gauges. I thought I have some serious problems. Thanks for the reply!

HarryD

Consistency is key. Most people here have a hard-on for 240 PSI across all cylinders.

With those numbers, if the car runs well, you should be fine.

Car Analogy

Same experience here. Bought HF gauge, got similar readings to yours. Perhaps even a little lower. Searched and found lots of similar complaints on here about the HF gauge.

Rented gauge from Autozone and redid the tests. Got in the mid 220 range.

Returned the HF gauge...

tama05

I had the same issue with a harbor freight gauge. The shrader valves are built into the gauge and not the hose that screws into the spark plug hole. I bought an OTC gauge and my readings jumped up by 50 psi across the board. Consistency is key, so your numbers are still good, but try a better gauge and compare results.

Charper732

I don't get where this mythical "consistency is key" came from. That is literally one of the dumbest things I see get constantly repeated on the forum. I've tested a legit 185psi with snap-on comp gauge across the board and the leakdown showed 45% leak at the rings. Along with other similar results on other engines. Consistency means NOTHING if the comp is actually low.

That being said. HF comp gauges are horrible. I've seen two guys use them and they both topped out at 180ish psi. Get a quality gauge or do a leakdown if you really want to know the health of your motor