I've been trying to diagnose this issue for 2 weeks now. This car is screwing up long planned trip to the SCCA San Diego NT and El Toro Pro. I've exhausted myself trying to diagnose this thing every day after work, and I think I'm finally closing in on the problem.

The whole thing started when my new, brand-new-in-box Greddy EMU made the car run really rich at the dyno for the base pull (10.0 AFRs at the upper RPM range). Disconnected it and the stock ECU still ran rich, 11.1 AFRs at the top end. Made very little power compared to another stock S2000 on that dyno (like 50 HP less peak, and less throughout the band).

I looked at sensor data and replaced a lot of parts, nothing seemed to work. My narrow band still reads rich.

Finally someone told me to check the compression so I went and bought a compression checker. 140-148 PSI warm for all 4 cylinders with the throttle held open. I did a wet compression test with a small amount of oil (half cap), 180 PSI wet.

People told me that wasn't enough info to make a bad-rings diagnosis. So, I bought a leakdown tester. I just got back from my friend who has a nice new compressor with a regulator. My leakdown goes to 100psi max. That's what i ran it at. Leakdown numbers: 2%, 3%, 2%, 5%.

I have heard two prevailing ideas.

1) PSI isn't great enough to overwhelm the rings, so, it's the rings because the numbers show there isnt' any gasket or valve leakage
2) Timing skipped a tooth

Thoughts, concerns, etc. Help me, sweet Jesus.

 

Your compression is very low. The Honda spec is 230-240 with no cylinder less than 140 IIRC. You are at the very bottom of the spec. If I had to guess you are not doing the leak-down test properly. On the set I have you must do a pressure set procedure to set the gauge pressure. On my Matco set I believe it usually runs around 35psi. Running it wide open will throw the results. Here's a youtube vid that may help a bit.

[media]http://www.youtube.com/watch?v=ofSiTGeLXvc[/media]

 

Yeah, I'm aware my compression is low, that's why I did a wet compression test, to help verify it was the rings.

I did do the test correct as per my leak-down tester's instructions. The procedure for mine is to set the PSI on the gauge 10PSI lower than the regulator on the air compressor. We set that the regulator to 110, set the gauge to 100 (which on mine moves both the gauges to 100) . Then, when I connected the quick disconnect, it barely dropped. We verified leak-down gauge functionality by rotating it past TDC and then hearing exhaust valve leak (and the PSI fall).

 

Then it almost has to be timing. Pull the valve cover and check.

 

Check valve clearances and adjust as necessary. Sounds like you're due for a valve adjustment.

 

Valve adjustment done about 4k miles ago. I didn't check the chain when I had it open. I wish I had.

 

In that case, double check. Timing chains don't just jump teeth, it is not a common occurence.