Cylinder 3/4 misfire

[brpbowma]

Hi, I have a 1997 Honda Civic HX. Recently, my check engine light came on. Pulled the codes - 73 Cylinder 3 Misfire, and 74 Cylinder 4 misfire. Cleared out the codes, tried driving again. After perhaps 5-6 driving cycles, the engine light came on again. Same codes. Replaced the spark plugs, and ran a can of Techron through it. Another 7-8 driving cycles, and it came on again today. Interestingly enough, I notice no drop in power, and the engine runs smoothly... no pinging, knocking, etc. I have a couple of questions: 1. Does the check engine light require an error like a multiple cylinder misfire to be persistent (i.e., constant across multiple driving cycles) before it turns on? Or is it triggered as soon as the fault occurs? If the latter is true, I seem to have an intermittent problem. 2. Prior to the light coming on, I had a break in my exhaust (pipe rusted through just at the joint to the rear muffler. I drove it that way for a couple of weeks before finally replacing the muffler. Could this have contributed to a condition that is now causing the intermittent misfire? 3. Last emissions inspection, the car would not pass. Seemed to be burning lean. I replaced the O2 sensor. Took it back. Was still burning lean, but the tech got it to pass by testing at higher RPM's. Wondering now if this could be part of the same problem? Just thought I'd check before I start replacing more parts... (plug wires, etc.) Thanks! Brian

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[brianbu01]

1. It has to have a misfire for atless 2 cycles, but if it had a constant misfire in a cylinder it would probably turn on right away.
2. Nope
3 ? My state we use a OBD2 connection to test 96+ which just reinsures the check engine light isn't on and it has gone threw a few drive cycles. With 2 speed idle tests just letting the car heat up for a bit before testing will sometimes allow it to do better and pass.


I would replace wires, cap and rotor with plugs. Wires are like 50 bucks cap and rotor are like 20. It is just apart of tuning it up. If it is still misfiring I would look at the injectors.

Do you know how tight to tighten a spark plug? Sometimes misfires come from not tightening a spark plug enough. People are typically scared of breaking one off, thank god I haven't ever broke one. To install a spark plug first you line the treads up using just the extention. Once lined up tighten until the pressure you are applying changes. This is where you want to pay attention. Continue to turn with this same pressure until the plug hits a spot where the pressure needed to turn increases again and that is how tight you want them.