My 2000 Civic em1 developed a miss last week and I am at my wits end. I was running about 4000 rpm in 5th gear when suddenly cel started blinking. Limped the car home and put it on the code scanner. Read the codes and got a p1399 and p0301. Changed plugs, rotor, cap, changed plug wires around still have the miss. Has strong spark on all cylinders now. Looking in spark plug hole piston looks wet and smells like gas. No water in oil or vice versa. What else could it be?

 

First do a compression test, it could be mechanical failure such as a burnt valve. If you don't have a compression tester, a quick thing you can do is unplug the low voltage wires at the distributor so it can't start, then crank to see if it sounds normal. If you hear an uneven pattern with a once-around speedup of the starter, there is a cylinder with zero compression. Of course a compression tester is more conclusive.

 

I have been hunting for my compression tester for days now. I had never heard about that trick before that is pretty neat. I'll go outside and try that shortly.

 

you can get a compression tester for "free" at many parts stores,
just leave a $20 or so refundable deposit. lots of other
tools too like giant c-clamp for bushings but takes more $$$.

 

I found my compression tester finally so first thing in the morning I will post the update. Might be planning a build next lol.

 

P1399 is a pending random misfire code which tells me it's likely systemic and not cylinder specific. Do you have a scan tool available to you? If you do, check the mode 6 data and see which cylinders are misfiring. We know #1 is for sure, but the 1399 is unlikely to have set unless there were at least 1 other cylinder misfiring. This is just a guess based on the information you've provided, but I'd bet it's the distributor.

 

Use a piece of PVC pipe or an auto stethoscope against the offending cylinder's fuel injector and listen for pulse/firing (ticking sound). If it's not firing then test harness for voltage..if harness is good replace fuel injector. If it is firing it doesn't mean the fuel injector is working properly..it could be leaking internally. Disconnect fuel injector harness while engine is idling and listed for rpm's to drop (drop/power balance test). The rpms should drop and if they don't there's an issue with either spark, fuel or air (compression in this case). Remove the offending cylinder's spark plug and check it's anode for fouling or wetness (unburned fuel). If it's appearance is white then it idicates a lean burn and little or no fuel getting to the cylinder.

Can also do an additional drop test by removing spark-plug wire from spark plug and listen for rpm's to drop..that test spark but not fuel.
As already mentioned perform a compression test by:
1) Put a charger on the battery prior and during test to ensure optimal cranking. Weak cranking can effect results.
2) Press gas pedal all the way down to shut off injectors during cranking
3) Have someone crank the engine while you watch the compression gauge..note compression gauge fluctation as well as the highest reading. Crank a few times past the highest reading to ensure optimal reading.
4) Cylinders should be with 10-20% of each other. Any cylinder with a low reading do a wet (one teaspoon of engine oil) test. Do all four cylinders if you want.

Here's a good video on compression testing. Disregard what he says about 5 to 6 cranks as it could take more and as mentioned..go two or three cranks past highest reading: