Chr1s7ian

Hey guys normally I try to find old threads or information from other sources but long story short I got a P1399 cylinder misfire on my stock 90k mile 2000 s2k and before replacing every single thing, I rented a compression tester from auto zone. While taking off the coil packs and spark plugs, #1 coil pack was extremely dirty compared to the rest and I've already read other threads regarding that so lets continue. I had already seen online that the reviews were horrible for the auto zone compression tester (1 of 5 stars) but I figured I'd give it shot anyway since I get my money back regardless. When I returned home I realized the compression tester didn't have O rings anywhere, already a red flag but I did the test anyway. It was at 175+/- 5 psi and held for every cylinder, I know this is low but should I rely on the auto zone tester? My logic is that if the tester was bad, the gauge would've released pressure but it held. Maybe the threads into the spark plug hole have a leak but the instant the pressure built to 175 on the gauge it was locked in by the properly working gauge. Btw the adaptor that threads into the spark plug hole is what didn't have the O ring that concerned me. I kind of have to "guess" how far to thread.

I'm still learning and I love reading the knowledge you guys have so I'd like some insight on your opinions.

BTW I know this is long but I've seen the hate some people get for not including ANY information.

rpg51

The most important thing is that the compression results for each cylinder are similar and it appears yours are. But, yes, if you are testing compression a decent compression tester will give you more reliable and accurate results.

Car Analogy

Except I'm wondering if the missing o ring is making it so that anything over 175 psi leaks out to exactly 175 psi. If so, that could mean its still possible there is some variation.

Get a working gauge. Do not get the HF one. Its junk (for teading high psi in high compression ratio engines like ours) even when its new.

The AZ one is actually quite good when its in decent shape. Find another AZ and see if their gauge looks better before you rent it.