Spiff-07

Hey guys long time reader here! First time poster!

I'm having some problems with my 2003 S2000 API.

I have CEL light on and the car runs very rough at idle. Misfires under 2000 RPM and has 50 percent compression on C4. After 3000 it runs fine and seems good on power.

The motor has 120,000 miles on it and the car was bought 2nd hand from a military type. My guess is she's had a rough life.

Spark plugs and coil packs are all good. Just had a valve adjustment and it did not help. Maybe dirty injectors? But that shouldn't cause low compression.

I'm hoping it's a sensor issue but the guys at the shop think its a burnt valve. I think they are right.

I was hoping that one of you guys had some advice on where to start? I read through the sticky and it gave me some great ideas and was wondering if anyone had some more ideas for my Sunday run down.

I would appreciate any help!

AP1Driver

You're on the right track. Pull the valve cover and check the clearances on the valves. 0.10 exhaust side, .08 intake side. Cold engine. If all the valves are in spec or the exhaust valves aren't excessively tight, you likely have a bent or burnt valve. Check the retainers (small circlips on top of the valve retainers in the center). If they are recessed deeply on any valve(s), you have a cracked retainer, which won't contribute to this problem, but could have been caused by an over-rev (missed downshift), which could have also bent a valve or valves.

Provide more info at that point. Does your CEL flash or is it steady? What do the spark plugs look like? This could be multiple other things besides a valve issue...

Spiff-07

Hey!

Thanks for the response, I'll find out at first light! During the valve adjustments I would hope they got the valves within spec. The CEL is flashing. Plugs and coil packs are 5k old and were rearranged, same problem. I don't know if the MAP sensor was checked at the shop but wouldn't I also have hesitation and bog down at higher rpms? Sorry, don't know much about that.

Cheers

AP1Driver

I'd park it until you figure it out... If the CEL is flashing and it's missing that bad then you're likely fuel soaking your oil and diluting it, which is a big no no for engine health. MAP is very unlikely. Do another comp test and leak-down as well...

Spiff-07

Yup, sitting all lonely in the parking lot.

Spiff-07

The way I see it it's got to be ignition, fuel or compression.

So the plan for the day:

Easy Stuff First
Run scanner looking for bad ignition coil - Unlikely
Recheck plugs/plug wires/coil packs - Unlikely
Check PCM voltage - Very Unlikely
Look for large vacuum leaks - Very Unlikely unless the low compression caused the leak
Flutter test for burnt exhaust valve - We'll see
Check for cracked valve retainers - I hope not but who knows with the campus special valve adjustments checking it out.
Valve clearance - see above
Block test for leaky head gasket - unlikely
Rearrange injectors - Hoping its this but can't see why I would have low compression.

Any suggestions?

AP1Driver

Start with checking the valves. And then a leak down and another compression test.

AP1Driver

Better yet, check your spark plugs first. If no dice, start with the valves.