2014 Civic P0303 Code before and after engine replacement

Car Details: 2014 Honda Civic LX, 1.8L, 4 Cyl, 180k miles

Question: What potential causes are there of a recurring cylinder misfire after replacing the original engine with a low mileage used engine?


Issue first occurred when driving downhill on the highway. Check engine light and the following warnings came on at the same time: Check TPMS, Check Emissions System, Hill Start Assist, Check VSA, Check Power Steering Assist. Took it to AutoZone and got a P0303 code reading. Car was off overnight and the next day check engine and all warnings had cleared and car drove normally for months.

Issue next occurred when stopping at stop sign from low speed. Check engine and the same set of warnings came on. The car began rough idling, had slow acceleration, and power loss.

The code it read was again P0303. A mechanic replaced plugs and coils and it passed test drive. Drove the car away and 20 miles down the road the same warnings and symptoms began again, so took it back. Mechanic couldn’t diagnose, so took it to dealership who diagnosed as the following: likely bent intake valve due to 100% leak down of 3rd cylinder and air coming out of intake box.

Recommendation was replace engine immediately, rather than find cause and rebuild/repair, so I had the engine replaced with a used engine with 44k miles and a 3 year parts/labor warranty. After driving normally for over 50 miles the same warnings and symptoms occurred once again. After leaving the car off for 2 hours, the warnings remained but the car drove normally for another hour. It once again has a cylinder misfire.

The only thing not touched is the wiring to coil #3. That would be my starting point.


Motor #1 has bad valve and misfire. dealer tested ignition first or jumped right to burnt valve? ign is “good”. must be a compression/valve issue. yep

Replace engine, cylinder 3 still misfires, wouldn’t you know it! … lol … sorry, not making fun, just a very unexpected and somewhat humorous thing (for everyone but you) to happen. Tommy (of Tom and Ray, Car Talk fame) would have said “Doesn’t anybody screen these posts?” … lol

Back to the issue, p0303 (which imo needs to be the first priority to resolve) means the computer issued the command to fire the cylinder 3 spark plug, but upon measuring the speed of the crankshaft after the firing , it failed to speed up like it should have. Common sense says to look first at these things

  • Computer may have issued command to fire, but did spark actually make it to the tip of the plug? (Wiring problem, coil for number 3 plug problem)
  • Did computer issue command to fire at the proper time ? And did it fire at the right time?
    (Engine timing problem.)
  • Is the fuel injector feeding cylinder 3 working properly? (first check, noid light)
  • Is computer measuring the crankshaft speed accurately? (crank position sensor problem).

Just my two cents but you likely know what it isn’t now. I’m thinking the wire harness for injectors may not have been replaced with the engine. I’m not qualified to say the other engine was shot or not but I if he got no reading, maybe.

On second thought, if all the lights are coming on and not just the misfire code, that would suggest more a computer, ground, etc.