I got a check engine light on my 2000 S2000 and the code indicated cylinder 1 misfire. I checked the plugs and retightened them and then I cleared the codes in the ECU and the CEL went away for about a few days and then it came back on.

I ran a compression check and found the following:

235 (rear cylinder)
240
240
about 140 (front cylinder)

I put some oil into the low cylinder and tried again. Got 210 or so.

So, I thought it must be bad rings. But then I read on the internet somewhere that if you put TOO much oil in, that makes the test bogus and it still could be a valve.

What is the experience of the board? With one bad cylinder, does it usually turn out to be a bad ring or a bad valve.

The car idles slightly "off", but only a car person would ever notice. It makes good power and drives almost perfectly really. The engine has 20,000 miles on it.

Should I re-do the test and only put a SMALL amount of oil in it? Or should I just assume it's a bad block/ring/piston and consider options from there? I have experience rebuilding engines and heads... but I don't relish the idea of doing any of that in winter!

Thanks much!

 

Do a leakdown test. it will tell you if it's rings or valves or the headgasket.

 

Do you have the extended warranty? I'm sure hondacare would take care of this.

 

Slows2k: I am not sure exactly how the proper way to do this is. I did make a casual observation of how fast the pressure dropped after I stopped cranking. On all four cylinders, it dropped at about the same rate. I would say it took about 5 seconds to lose each 10 PSI, but I'm just guessing. They all dropped at approximately the same rate by just eyeing it. In other words, it's not like one cylinder plummeted back down compared to the others.

SilverKnight:
No, I don't have the warranty, I am the second owner... I've had the car about 8 months, and this problem just popped up in the last 1-2 months or so.

Actually I was thinking of complaining to Honda. My last two Honda products have been pretty bad (RSX-S and now this S2000). I know they probably won't DO anything about it, and that's OK, but I want to let them know they're slipping.

 

A leakdown test is done using a leakdown gauge/tester.

You pressurize the cyl. with air, then measure the air leakage on the 2nd gauge. you listen for air escaping through the crankcase. Lots of air coming out of the oil cap points at the rings. A valve seal issue will have a leakout the tailpipe, or intake. A leak to the coolant jacket will have air bubbles in the radiator.

I'm not sure why people insist on a compression test. A leakdown takes only a bit more time and is a more thorough check.