Scotty, my friend has a 2000 S2000, F20C 2.0L engine, 124k miles. I’ve been helping him with the repair. It generates random codes. P0302, P0303, P0304 is the most common, P0410 and P1411. Was a bad coil on cylinder 4 and we replaced it. It keeps giving a misfire code. We did the obvious stuff like moving plugs around to see if the misfire would change. Sometimes on 2 sometimes on 3 never on 1. It has new spark plugs, the one new coil, mechanical compression and leak down both within specs. Fuel pressure and volume within specs and ran cleaner through the injectors too. Also Honda code 1399. We are stumped.
Hook your scanner back up and look at the Freeze Frame data from when those codes are getting thrown. (don't worry about the air pump codes).
Look at the engine coolant temperature, the rpms, MAF, and the fuel trims.
Is there a pattern of these codes getting thrown at lower rpms whether the engine is warmed up or not, (vacuum hose/PCV valve, PCV valve hose), or only before the engine is warmed up at lower rpms (intake manifold gasket leak).
Switch to Live Data. Are the fuel trims higher Positive during lower rpms (idle) and then return closer to 0 at higher rpms? (again, vacuum leak).
If those P0302, P0303, P0304 codes are getting thrown above (around) 1500 rpms+, it's likely not a vacuum leak.
On the other hand, what if that P1399 code is the "tip off"?
Then it's time to consider if the EGR valve may be misbehaving.
They either mechanically fail (unlikely) or get "carboned up" and get stuck, or they operate fine and just their passages get "carboned up" and restrict EGR flow.
So, if the EGR valve is stuck open a little you'd be seeing higher Negative fuel trims at idle (if it were stuck open a lot, it's unlikely a cold engine would start).
(the EGR valve shouldn't be open at idle. If it is, exhaust gasses will displace some of the air (oxygen) that the MAF sensor is reporting that's going into the intake manifold (and the combustion chambers). Less air (oxygen) going INTO the intake means the O2 sensor is going to read less air (oxygen) in the exhaust.
The computer will interpret this as a "rich condition" (and technically it is) and respond with Negative fuel trims at idle.
So there's another place to look for a clue.
Also, what if the EGR passages are clogged with carbon and the EGR valve is opening/closing just fine? Here, you wouldn't see high Negative fuel trims at idle (the EGR valve is supposed to be closed at idle). But, when the car is cruising along under light load, steady speed maybe 45+ mph (and the computer commands the EGR valve to open), you'd see the fuel trims Positive because the computer doesn't expect that much air (oxygen) to be in the exhaust. It expects non-combustible exhaust gasses to be displacing some of the O2 in the combustion chambers. (computer sees a Lean condition).
If you stick around the forum long enough you might think that I'm too eager to blame electrical circuit/component issues.
But you have new spark plugs and your compression/leak down tests proved out fine, and your fuel pressure is good.
If your Maf sensor is reading close to 2g/s at idle, and the fact that I can't blame MULTIPLE misfire codes on 3 cylinders on 3 fuel injectors going bad at the same time, I'm leaning towards an issue on the "air side" of the air/fuel ratio
Thanks for this. I mean to say this weeks ago.
Check the timing it's possible it jumped a tooth. Also check out the wiring harnesses for coils. You can use a multimeter and check the resistance of the fuel injectors as well. Fuel system cleaner doesn't always work . Did you guys replace any components. If yes make sure it the right part.
Vaccum leak somewhere???? Car is 22 years old, lots of old rubbers on that car.
