Hello all,

I had put in new OE NGK plugs in earlier in the spring and decided to check them out and see how they look @ ~1500 miles on them. I think that generally they look good, but the #2 cyl plug looks like it’s lean… just wanted to see if anyone that is knowledgeable can confirm.

For background, I’ve been on a Gernby Flashpro tune since 2014 ish. I’ve been trying to chase down knock counts that seem to happen at low-medium load between 2500 and 3500 rpm in Cyl 2 only. It’s seemingly totally random, some drives it never manifests, others I get dozens in a short amount of time. I’ve tried trimming the #2 cyl ignition -5 deg and fuel +5 and have been running that for the last couple weeks, but the knock counts haven’t really changed as a result.


All plugs, 1 through 4 starting from the left

#1 close-up

#2 close-up

#3 close-up

#4 close-up

 

Cylinder 2 is burning a little more oil than the other 3. Might have lower compression, check valve clearance

The rpm range you mention is where there is greatest mean effective cylinder pressure. The oil you burn lowers octane rating. Not to mention a fouling plug won't spark as well. What you're experiencing is LSPI, and if you're burning oil, vacuum on decel may be contributing. What kind of oil are you using? New GF6 oils have additives to prevent LSPI. Might also have carbon deposits on the piston that are contributing.

 

Thanks for the reply. I adjusted the valves earlier this spring; the exhaust valves were tight (0.005/0.006) and were adjusted to Billman’s spec (0.012 I believe). I’ll definitely check the valves for #2 cyl to rule that out.

I did get a compression test done a long time ago (2015 I believe), and #2 cylinder was showing ~8% lower compression than the rest.

I didn’t think the S2000 was susceptible to LSPI as from what I read, it’s more of a problem on turbocharged direct injection engines. I’m also running Amsoil Sig Series 0w-30, which is stated to have additives to help with LSPI. If Cyl 2 is burning oil, it’s not much; I haven’t had to add oil between oil changes and I do them every spring (~5k miles). I suppose the plugs do confirm the knock counts I’m getting is not ghost knock, which is unfortunate.

 

Can you feel the misfire?

 

It can be heard and seen on telemetry. LSPI mostly happens on turbo motors, but it can happen with any high compression ratio engine. Boost means a higher effective compression ratio, as does increasing the geometric CR. In both instances the cylinder pressure increases.

 

Engine feels normal when these knock counts happen. No hesitation or knock noise. No knock counts at WOT, only at low/mid throttle at 2500-3500 rpm. But from looking at the spark plug it seems like there may be some actual knock.